Modern Blood Banking & Transfusion Practices - Denise Harmening ( 6ª edition ) [PDF] | Online Book Share (2024)

669 Pages • 452,462 Words • PDF • 20.4 MB

+ Modern+ Denise+ BLOOD+ Edition+ Banking+ practices+ Transfusion+ Harmening

Uploaded at 2021-07-04 02:41

Report DMCA

PREVIEW PDF

2682_IFC 22/05/12 12:11 PM Page 2

Antigen-Antibody Characteristic Chart* ANTIGENS Antigen System

Antigen Name

ISBT Name

Antigen Freq. % W B

RBC Antigen Expression at Birth

Antigen Distrib. Plasma/RBC

Demonstrates Dosage

Antigen Modification Enzyme/Other

D

RH1

85

92

strong

RBC only

no

Enz. ↑

C E

RH2 RH3

70 30

34 21

strong strong

RBC only RBC only

yes yes

Enz. ↑ Enz. ↑

c e

RH4 RH5

80 98

97 99

strong strong

RBC only RBC only

yes yes

Enz. ↑ Enz. ↑

ce/f Ce Cw

RH6 RH7 RH8

64 70 1

rare

strong strong strong

RBC only RBC only RBC only

no no yes

Enz. ↑ Enz. ↑ Enz. ↑

G V

RH12 RH10

86 1

30

strong strong

RBC only RBC only

no no

Enz. ↑ Enz. ↑

VS

RH20

1

32

strong

RBC only

no

K

KEL1

9

rare

strong

RBC only

occ

Enz. → AET+ ↓ ZZAP ↓++

k Kpa

KEL2 KEL3

98.8 2

100 rare

strong strong

RBC only RBC only

occ occ

Enz. → AET+ ↓ ZZAP ↓++ Enz. → AET+ ↓ ZZAP ↓++

Kpb Jsa

KEL4 KEL6

99.9 .01

100 20

strong strong

RBC only RBC only

occ occ

Enz. → AET+ ↓ ZZAP ↓++ Enz. → AET+ ↓ ZZAP ↓++

Jsb †Kx

KEL7 —

99.9 99.9

99 99.9

strong weak

RBC only RBC low

occ occ

Enz. → AET+ ↓ ZZAP ↓++ Enz. → AET+ ↓ ZZAP ↓++

FYa

FY1

65

10

strong

RBC only

yes

Enz. ↓ AET ↓ ZZAP ↓

FYb

FY2 FY3

80 100

23

strong strong

RBC only RBC only

yes no

Enz. ↓ AET ↓ ZZAP ↓ Enz. → AET → ZZAP →

FY5

100

?

?

no

Enz. → AET → ZZAP →

•FY6

100

?

RBC only

?

Enz. ↓ AET → ZZAP ↓

Rh

Kell

Duffy ?

*This chart is to be used for general information only. Please refer to the appropriate chapter for more detailed information. AET = 2-aminoethylisthiouronium bromide; ↑ = enhanced reactivity; → = no effect; ↓ = depressed reactivity; occ = occasionally; CGD = chronic granulomatious disease; HDN = hemolytic disease of the newborn; HTR = hemolytic transfusion reaction; NRBC = non-red blood cell; RBC = red blood cell; WBC = white blood cell; ZZAP = dithiothreitol plus papain. • No human antibody to FY6 has been reported. † It has been found that Kx is inherited independently of the Kell system; consequently it is no longer referred to as K15.

2682_IFC 22/05/12 12:11 PM Page 3

ANTIBODIES Immunoglobin Class IgM IgG

Optimum Temperature

Clinical Significance HTR HDN

yes

warm

yes

yes

occ occ

yes yes

warm warm

yes yes

yes yes

no no

occ occ

yes yes

warm warm

yes yes

yes yes

yes yes yes

no no no

occ occ occ

yes yes yes

warm warm warm

yes yes yes

yes yes yes

occ occ

yes yes

no no

occ occ

yes yes

warm warm

yes yes

yes yes

RBC

occ

yes

no

occ

yes

warm

yes

yes

RBC

occ

yes

some

occ

yes

warm

yes

yes

RBC RBC

no no

yes yes

no no

rarely no

yes yes

warm warm

yes yes

yes yes

RBC RBC

rarely rarely

yes yes

no no

rarely rarely

yes yes

warm warm

yes yes

yes yes

RBC RBC

no no

yes yes

no no

no occ

yes yes

warm warm

yes yes

yes yes

RBC

rare

yes

some

rare

yes

warm

yes

yes

RBC RBC

rare no

yes yes

some rarely

rare no

yes yes

warm warm

yes yes

yes yes

RBC

no

yes

?

no

yes

warm

Stimulation

Serology Saline AHG

Comp. Binding

RBC

occ

yes

no

occ

RBC RBC/NRBC

occ occ

yes yes

no no

RBC RBC

occ occ

yes yes

RBC RBC RBC/NRBC

occ occ occ

RBC RBC

Comments Very rarely IgA anti-D may be produced; however, this is invariably with IgG. Anti-E may often occur without obvious immune stimulation. Warm autoantibodies often appear to have anti-e-like specificity. Anti-Cw may often occur without obvious immune stimulation. Antibodies to V and VS present problems only in the black population, where the antigen frequencies are in the order of 30 to 32. Some antibodies to Kell system have been reported to react poorly in low ionic media. Kell system antigens are destroyed by AET and by ZZAP. Anti-K1 has been reported to occur following bacterial infection. The lack of Kx expression on RBCs and WBCs has been associated with the McLeod phenotype and CGD. Fya and Fyb antigens are destroyed by enzymes. Fy (a–b–) cells are resistant to invasion by P. vivax merozoites, a malaria-causing parasite. FY3 and 5 are not destroyed by enzymes. FY5 may be formed by interaction of Rh and Duffy gene products. FY6 is a monoclonal antibody which reacts with most human red cells except Fy(a–b–) and is responsible for susceptibility of cells to penetration by P. vivax. (Continued on inside back cover)

2682_FM_i-xvi 22/05/12 2:12 PM Page i

Modern Blood Banking & Transfusion Practices SIXTH EDITION

2682_FM_i-xvi 22/05/12 2:12 PM Page ii

Online Resource Center DavisPlus is your online source for a wealth of learning resources and teaching tools, as well as electronic and mobile versions of our products.

Visit davisplus.fadavis.com

Students

Instructors

Unlimited free access.

Upon Adoption.

Sign up today to see what’s available for your title.

Password-protected library of title-specific, online course content.

Taber’s online resources are now available across many of the DavisPlus resource pages. Look for this icon

to find Taber’s resources!

Explore more online resources from f.a.davis

www.DrugGuide.com

www.Tabers.com

www.LabDxTest.com

The complete Davis’s Drug Guide for Nurses® database with over 1,100 monographs on the web.

The power of Taber’s® Cyclopedic Medical Dictionary on the web. Find more than 60,000 terms, 1,000 images, and more.

The complete database for Davis’s Comprehensive Handbook of Laboratory and Diagnostic Tests with Nursing Implications online. Access hundreds of detailed monographs.

www.fadavis.com

2682_FM_i-xvi 22/05/12 2:12 PM Page iii

Modern Blood Banking & Transfusion Practices SIXTH EDITION Denise Harmening, PhD, MT(ASCP) Director of the Online Masters in Clinical Laboratory Management Adjunct Professor, Department of Medical Laboratory Science College of Health Sciences Rush University Chicago, Illinois, USA

2682_FM_i-xvi 22/05/12 2:12 PM Page iv

F. A. Davis Company 1915 Arch Street Philadelphia, PA 19103 www.fadavis.com Copyright © 2012 by F. A. Davis Company Copyright © 2012 by F. A. Davis Company. All rights reserved. This product is protected by copyright. No part of it may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without written permission from the publisher. Printed in the United States of America Last digit indicates print number: 10 9 8 7 6 5 4 3 2 1 Senior Acquisitions Editor: Christa Fratantoro Manager of Content Development: George W. Lang Developmental Editor: Nancy J. Peterson Art and Design Manager: Carolyn O’Brien As new scientific information becomes available through basic and clinical research, recommended treatments and drug therapies undergo changes. The author(s) and publisher have done everything possible to make this book accurate, up to date, and in accord with accepted standards at the time of publication. The author(s), editors, and publisher are not responsible for errors or omissions or for consequences from application of the book, and make no warranty, expressed or implied, in regard to the contents of the book. Any practice described in this book should be applied by the reader in accordance with professional standards of care used in regard to the unique circumstances that may apply in each situation. The reader is advised always to check product information (package inserts) for changes and new information regarding dose and contraindications before administering any drug. Caution is especially urged when using new or infrequently ordered drugs. Library of Congress Cataloging-in-Publication Data Modern blood banking & transfusion practices / [edited by] Denise Harmening.—6th ed. p. ; cm. Modern blood banking and transfusion practices Rev. ed. of: Modern blood banking and transfusion practices / [edited by] Denise M. Harmening. c2005. Includes bibliographical references and index. ISBN 978-0-8036-2682-9–ISBN 0-8036-2682-7 I. Harmening, Denise. II. Modern blood banking and transfusion practices. III. Title: Modern blood banking and transfusion practices. [DNLM: 1. Blood Banks—methods. 2. Blood Grouping and Crossmatching. 3. Blood Transfusion—methods. WH 460] 615'.39—dc23 2011047863 Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by F. A. Davis Company for users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that the fee of $.25 per copy is paid directly to CCC, 222 Rosewood Drive, Danvers, MA 01923. For those organizations that have been granted a photocopy license by CCC, a separate system of payment has been arranged. The fee code for users of the Transactional Reporting Service is: / + $.25.

2682_FM_i-xvi 22/05/12 2:12 PM Page v

To all students—full-time, part-time, past, present, and future—who have touched and will continue to touch the lives of so many educators. . . . It is to you this book is dedicated in the hope of inspiring an unquenchable thirst for knowledge and love of mankind.

2682_FM_i-xvi 22/05/12 2:12 PM Page vi

2682_FM_i-xvi 22/05/12 2:12 PM Page vii

Foreword Blood groups were discovered more than 100 years ago, but most of them have been recognized only in the past 50 years. Although transfusion therapy was used soon after the ABO blood groups were discovered, it was not until after World War II that blood transfusion science really started to become an important branch of medical science in its own right. In order to advance, transfusion science needs to be nurtured with a steady flow of new knowledge generated from research. This knowledge then must be applied at the bench. To understand and best take advantage of the continual flow of new information generated by blood transfusion scientists and to apply it to everyday work in the blood bank, technologists and pathologists must have a solid understanding of basic immunology, genetics, biochemistry (particularly membrane chemistry), and the physiology and function of blood cells. High standards are always expected and strived for by technologists who work in blood banks and transfusion services. I strongly believe that technologists should understand the principles behind the tests they are performing, rather than performing tasks as a machine does. Because of this, I do not think that “cookbook” technical manuals have much value in teaching technologists; they do have a place as reference books in the laboratory. During the years (too many to put in print) that I have been involved in teaching medical technologists, it has been very difficult to select one book that covers all of the information that technologists in training need to know about blood transfusion science without confusing them. Dr. Denise Harmening has produced that single volume. She has been involved in teaching medical technologists for most of her career. After seeing how she has arranged this

book, I would guess that her teaching philosophies are close to my own. She has gathered a group of experienced scientists and teachers who, along with herself, cover all of the important areas of blood transfusion science. The chapters included in Part I, “Fundamental Concepts” (including a section on molecular phenotyping), provide a firm base on which the student can learn the practical and technical importance of the other chapters. The chapters in Part II, “Blood Groups and Serologic Testing,” and Part III, “Transfusion Practice” (including a new chapter on cellular therapy), provide enough information for medical technologists without overwhelming them with esoteric and clinical details. Part IV covers leukocyte antigens and relationship (parentage) testing. The chapters in Part V, “Quality and Compliance Issues” (including new chapters on utilization management and tissue banking), complete the scope of transfusion science. Part VI: Future Trends describes tissue banking as a new role for the transfusion service. Although this book is designed primarily for medical technologists, I believe it is admirably suited to pathology residents, hematology fellows, and others who want to review any aspect of modern blood banking and transfusion practices.

GEORGE GARRATTY, PhD, FIBMS, FRCPath Scientific Director American Red Cross Blood Services Southern California Region and Clinical Professor of Pathology and Laboratory Medicine University of California, Los Angeles

vii

2682_FM_i-xvi 22/05/12 2:12 PM Page viii

2682_FM_i-xvi 22/05/12 2:12 PM Page ix

Preface This book is designed to provide the medical technologist, blood bank specialist, and resident with a concise and thorough guide to transfusion practices and immunohematology. This text, a perfect “crossmatch” of theory and practice, provides the reader with a working knowledge of routine blood banking. Forty-four contributors from across the country have shared their knowledge and expertise in 28 comprehensive chapters. More than 500 illustrations and tables facilitate the comprehension of difficult concepts not routinely illustrated in other texts. In addition, color plates provide a means for standardizing the reading of agglutination reactions. Several features of this textbook offer great appeal to students and educators, including chapter outlines and educational objectives at the beginning of each chapter; case studies, review questions, and summary charts at the end of each chapter; and an extensive and convenient glossary for easy access to definitions of blood bank terms. A blood group Antigen-Antibody Characteristic Chart is provided on the inside cover of the book to aid in retention of the vast amount of information and serve as a review of the characteristics of the blood group systems. Original, comprehensive step-by-step illustrations of ABO forward and reverse grouping, not found in any other book, help the student to master this important testing, which represents the foundation of blood banking. The sixth edition has been reorganized and divided into the following sections: • • • • • •

Part I: Fundamental Concepts Part II: Blood Groups and Serologic Testing Part III: Transfusion Practice Part IV: Leukocyte Antigens and Relationship Testing Part V: Quality and Compliance Issues Part VI: Future Trends

In Part I, the introduction to the historical aspects of red blood cell and platelet preservation serves as a prelude to the

basic concepts of genetics, blood group immunology, and molecular biology (including molecular phenotyping). Part II focuses on blood groups and routine blood bank practices and includes the chapters “Detection and Identification of Antibodies” and “Pretransfusion Testing.” It also covers current technologies and automation. Part III, “Transfusion Practice,” includes a new chapter called “Cellular Therapy” and covers the more traditional topics of donor screening, component preparation, transfusion therapy, transfusion reactions, and apheresis. Certain clinical situations that are particularly relevant to blood banking are also discussed in detail in this section, including hemolytic disease of the fetus and newborn, autoimmune hemolytic anemias, and transfusion-transmitted diseases. The human leukocyte antigens system and relationship testing are discussed in Part IV of the book. In Part V, quality and compliance issues are discussed, including a new chapter on utilization management. The chapters on quality management, transfusion safety and federal regulatory requirements, laboratory information systems, and legal and ethical considerations complete the scope of practice for transfusion services. Also included is the chapter “Tissue Banking: A New Role for the Transfusion Service,” which introduces another responsibility already in place in several institutions. This book is a culmination of the tremendous efforts of many dedicated professionals who participated in this project by donating their time and expertise because they care about the blood bank profession. The book’s intention is to foster improved patient care by providing the reader with a basic understanding of modern blood banking and transfusion practices. The sixth edition is designed to generate an unquenchable thirst for knowledge in all medical technologists, blood bankers, and practitioners, whose education, knowledge, and skills provide the public with excellent health care.

DENISE M. HARMENING, PhD, MT(ASCP)

ix

2682_FM_i-xvi 22/05/12 2:12 PM Page x

Contributors Robert W. Allen, PhD Director of Forensic Sciences Center for Health Sciences Oklahoma State University Tulsa, Oklahoma, USA

Lucia M. Berte, MA, MT(ASCP)SBB, DLM; CQA(ASQ)CMQ/OE President Laboratories Made Better! P.C. Broomfield, Colorado, USA

Maria P. Bettinotti, PhD Director, HLA & Immunogenetics Department Quest Diagnostics Nichols Institute Chantilly, Virginia, USA

Cara Calvo, MS, MT(ASCP)SH Medical Technology Program Director and Lecturer Department of Laboratory Medicine University of Washington Seattle, Washington, USA

Lorraine Caruccio, PhD, MT(ASCP)SBB National Institutes of Health Rockville, Maryland, USA

Judy Ellen Ciaraldi, BS, MT(ASCP)SBB, CQA(ASQ) Consumer Safety Officer Division of Blood Applications Office of Blood Research and Review Center for Biologics Evaluation and Research U.S. Food and Drug Administration Rockville, Maryland, USA

Julie L. Cruz, MD Associate Medical Director Indiana Blood Center Indianapolis, Indiana, USA

Paul James Eastvold, MD, MT(ASCP) Chief Medical Officer American Red Cross Lewis and Clark Region Salt Lake City, Utah, USA

Glenda A. Forneris, MHS, MT(ASCP)SBB Program Director/Professor Medical Laboratory Technology Program Kankakee Community College Kankakee, Illinois, USA

x

Ralph E. B. Green Associate Professor Discipline and Program Leader Discipline of Laboratory Medicine School of Medical Sciences RMIT University Melbourne, Australia

Steven F. Gregurek, MD Assistant Professor Clarian Health Indianapolis, Indiana, USA

Denise Harmening, PhD, MT(ASCP) Director of the Online Masters in Clinical Laboratory Management Adjunct Professor, Department of Medical Laboratory Science College of Health Sciences Rush University Chicago, Illinois, USA

Chantal Ricaud Harrison, MD Professor of Pathology University of Texas Health Sciences Center at San Antonio San Antonio, Texas, USA

Elizabeth A. Hartwell, MD, MT(ASCP)SBB Medical Director Gulf Coast Regional Blood Center Houston, Texas, USA

Darlene M. Homkes, MT(ASCP) Senior Technologist for Transfusion Services St. Joseph Hospital Kokomo, Indiana, USA

Virginia C. Hughes, MS, MLS(ASCP)SBB Director/Assistant Professor Medical Laboratory Sciences Dixie State College of Utah St. George, Utah

Patsy C. Jarreau, MLS(ASCP) Program Director and Associate Professor Department of Clinical Laboratory Sciences School of Allied Health Professions Louisiana State University Health Sciences Center New Orleans, Louisiana, USA

2682_FM_i-xvi 22/05/12 2:12 PM Page xi

Contributors

Susan T. Johnson, MSTM, MT(ASCP)SBB Director: Department of Clinical Education and Specialist in Blood Banking (SBB) Program, Blood Center of Wisconsin Director and Adjunct Associate Professor: Marquette University Graduate School, Transfusion Medicine Program Clinical Associate Professor: University of Wisconsin-Milwaukee, College of Health Sciences Associate Director: Indian Immunohematology Initiative Milwaukee, Wisconsin, USA

Melanie S. Kennedy, MD Clinical Associate Professor Emeritus Department of Pathology College of Medicine The Ohio State University Columbus, Ohio, USA

Dwane A. Klostermann, MSTM, MT(ASCP)SBB Clinical Laboratory Technician Instructor Moraine Park Technical College Fond du Lac, Wisconsin, USA

Barbara Kraj, MS, MLS(ASCP)CM Assistant Professor Georgia Health Sciences University College of Allied Health Sciences Department of Medical Laboratory, Imaging, and Radiologic Sciences Augusta, Georgia, USA

Regina M. Leger, MSQA, MT(ASCP)SBB, CMQ/OE(ASQ) Research Associate II American Red Cross Blood Services Southern California Region Pomona, California, USA

Ileana Lopez-Plaza, MD Division Head, Transfusion Medicine Department of Pathology and Laboratory Medicine Henry Ford Health System Detroit, Michigan, USA

Holli Mason, MD Director, Transfusion Medicine and Serology Director, Pathology Residency Training Program Harbor UCLA Medical Center Associate Clinical Professor David Geffen School of Medicine at UCLA Torrance, California, USA

Christine Pitocco, MS, MT(ASCP)BB Clinical Assistant Professor Clinical Laboratory Science Program School of Health Technology and Management Stony Brook University Stony Brook, New York, USA

Valerie Polansky, MEd, MLS(ASCP)CM Retired Program Director Medical Laboratory Technology Program St. Petersburg College St. Petersburg, Florida, USA

Karen Rodberg, MBA, MT(ASCP)SBB Director, Reference Services American Red Cross Blood Services Southern California Region Pomona, California, USA

Susan Ruediger, MLT, CSMLS Senior Medical Technologist Henry Ford Cottage Hospital Henry Ford Health System Grosse Pointe Farms, Michigan, USA

Kathleen Sazama, MD, JD, MS, MT(ASCP) Chief Medical Officer LifeSouth Community Blood Centers, Inc. Gainesville, Florida, USA

Scott Scrape, MD Assistant Professor of Pathology Director, Transfusion Medicine Service The Ohio State University Medical Center Columbus, Ohio, USA

Burlin Sherrick, MT(ASCP)SBB Blood Bank Supervisor and Adjunct Clinical Instructor Lima Memorial Hospital Lima, Ohio

Ann Tiehen, MT(ASCP) SBB Education Coordinator (f), Retired North Shore University Health System Evanston Hospital Department of Pathology and Laboratory Medicine Evanston, Illinois, USA

Kathleen S. Trudell, MLS(ASCP)CM SBBCM Gerald P. Morris, MD, PhD Research Instructor Department of Pathology and Immunology Washington University School of Medicine Saint Louis, Missouri, USA

Clinical Coordinator—Immunohematology Clinical Laboratory Science Program University of Nebraska Medical Center Omaha, Nebraska, USA

Phyllis S. Walker, MS, MT(ASCP)SBB Donna L. Phelan, BA, CHS(ASHI), MT(HEW) Technical Supervisor HLA Laboratory Barnes-Jewish Hospital St. Louis, Missouri, USA

Manager, Immunohematology Reference Laboratory, Retired Blood Centers of the Pacific San Francisco, California, USA

xi

2682_FM_i-xvi 22/05/12 2:12 PM Page xii

xii

Contributors

Merilyn Wiler, MA, MT(ASCP)SBB Customer Regulatory Support Specialist Terumo BCT Lakewood, Colorado

Alan E. Williams, PhD Associate Director for Regulatory Affairs Office of Blood Research and Review Center for Biologics Evaluation and Research U.S. Food and Drug Administration Silver Spring, Maryland, USA

Elizabeth F. Williams, MHS, MLS(ASCP)CM, SBB Associate Professor Department of Clinical Laboratory Sciences School of Allied Health Professions LSU Health Sciences Center New Orleans, Louisiana, USA

Scott Wise, MHA, MLS(ASCP), SBB Assistant Professor and Translational Research Laboratory Manager Medical College of Georgia Department of Biomedical and Radiological Technologies Augusta, Georgia, USA

Gregory Wright, MT(ASCP)SBB Manager, Blood Banks North Shore University Health System Evanston, Illinois, USA

Patricia A. Wright, BA, MT(ASCP)SBB Blood Bank Supervisor Signature Healthcare-Brockton Hospital Brockton, Massachusetts, USA

Michele B. Zitzmann, MHS, MLS(ASCP) Associate Professor Department of Clinical Laboratory Sciences LSU Health Sciences Center New Orleans, Louisiana, USA

William B. Zundel, MS, MLS(ASCP)CM, SBB Associate Teaching Professor Clinical Laboratory Sciences Department Associate Professor Department. of Microbiology and Molecular Biology Brigham Young University Provo, Utah, USA

2682_FM_i-xvi 22/05/12 2:12 PM Page xiii

Reviewers Terese M. Abreu, MA, MLS(ASCP)CM Director, Clinical Laboratory Science Program

Wyenona Hicks, MS, MT(ASCP)SBB

Judith S. Levitt, MT(ASCP)SBB Clinical Laboratory Manager

College of Arts and Sciences

Assistant Professor, Program in Clinical Laboratory Sciences

Heritage University

College of Allied Health Sciences

University of Iowa Hospitals and Clinics

Toppenish, Washington, USA

University of Tennessee Health Science Center

Iowa City, Iowa, USA

DeGowin Blood Center, Department of Pathology

Memphis, Tennessee, USA

Deborah Brock, MHS, MT(ASCP)SH

Beverly A. Marotto, MT(ASCP)SBB

Instructor, Medical Laboratory Technology Program

Adjunct Faculty, Online Specialist in Blood Bank (SBB) Certificate Program

Allied Health Department

Rush University

Lahey Clinic

Faculty Liaison for Professional Development

Chicago, Illinois, USA

Burlington, Massachusetts, USA

Academic Affairs Department Tri-County Technical College Pendleton, South Carolina, USA

Lynne Brodeur, MA, BS (CLS) Lecturer Department of Medical Laboratory Science College of Arts & Sciences University of Massachusetts–Dartmouth North Dartmouth, Massachusetts, USA

Cynthia Callahan, MEd, MLS(ASCP) Program Head, Medical Laboratory Technology School of Health & Public Services Stanly Community College Locust, North Carolina, USA

Kay Doyle, PhD, MLS(ASCP)CM Professor and Program Director, Clinical Laboratory Sciences/Medical Laboratory Science

Shelly Hitchcox, RT (CSLT)

Blood Bank Manager, Blood Bank Department

Tina McDaniel, MA, MT(ASCP)

Medical Technologist

Program Director, Medical Laboratory Technology

Blood Bank Department

School of Health, Wellness, & Public Safety

Fletcher Allen Healthcare

Davidson County Community College

Burlington, Vermont, USA

Thomasville, North Carolina, USA

Judith A. Honsinger, MT(ASCP) Associate Professor

Dora E. Meraz, MEd, MT(ASCP)

Health & Human Services Department

Laboratory Coordinator, Clinical Laboratory Sciences Program

River Valley Community College

College of Health Sciences

Claremont, New Hampshire, USA

The University of Texas at El Paso El Paso, Texas, USA

Fang Yao Stephen Hou, MB(ASCP)QCYM, PhD Assistant Professor, Clinical Laboratory Science Department

Gretchen L. Miller, MS, MT(ASCP) MLT Program Director, Assistant Professor

College of Health Sciences

Brevard Community College

Marquette University

Heath Science Institute

Milwaukee, Wisconsin, USA

Cocoa, Florida, USA

Stephen M. Johnson, MS, MT(ASCP)

Janis Nossaman, MT(ASCP)SBB

Department of Clinical Laboratory and Nutritional Sciences

Program Director, School of Medical Technology Saint Vincent Health Center

Manager, Donor Collections and Transfusion Services

University of Massachusetts–Lowell

Erie, Pennsylvania, USA

Exempla St. Joseph Hospital Denver, Colorado, USA

Lowell, Massachusetts, USA

Vanessa Jones Johnson, MBA, MA, MT(ASCP) Joyce C. Foreman, MS(CLS), MT(ASCP)SBB

Karen P. O’Connor, MT(ASCP)SBB

Blood Bank Team Leader

Program Director, Pathology & Laboratory Medicine Service

Clinical Laboratory Department

Overton Brooks VA Medical Center

Laboratory Instructor, Department of Medical Technology

Baptist Medical Center South

Shreveport, Louisiana, USA

College of Health Sciences

Montgomery, Alabama, USA

Michelle Lancaster Gagan, MSHS, MT(ASCP)

University of Delaware

Douglas D Kikendall, MT(ASCP)

Newark, Delaware, USA

Blood Bank/Phlebotomy Supervisor

Janet Oja, CLS (NCA)

Instructor/Education Coordinator

CLS Instructor, Blood Bank Department

Medical Laboratory Technology Program

Yakima Regional Hospital

Immunohematology Instructor

Health and Human Services Department

Yakima, Washington, USA

Department of Medical Laboratory Sciences

York Technical College

Weber State University

Rock Hill, South Carolina, USA

Ogden, Utah, USA

xiii

2682_FM_i-xvi 22/05/12 2:12 PM Page xiv

xiv

Reviewers

Susan H. Peacock, MSW, MT(ASCP)SBB, CQA(ASQ)

Barbara J. Tubby, MSEd, BS, MT(ASCP)SBB

Meridee Van Draska, MLS(ASCP)

Supervisor of Blood Bank

Program Director, Medical Laboratory Science

Manager, Quality Assurance Department

Guthrie Health

Department of Health Sciences

Gulf Coast Regional Blood Center

Sayre, Pennsylvania, USA

Illinois State University Normal, Illinois, USA

Houston, Texas, USA

Emily A. Schmidt, MLS(ASCP)CM Clinical Instructor, School of Medical Technology Alverno Clinical Laboratory at St. Francis Hospital and Health Centers Beech Grove, Indiana, USA

Amber G Tuten, MEd, MT(ASCP), DLM(ASCP)CM Assistant Professor, Clinical Laboratory Science Program Thomas University Thomasville, Georgia, USA

2682_FM_i-xvi 22/05/12 2:12 PM Page xv

Contents Part I:

18. Transfusion-Transmitted Diseases

Fundamental Concepts 1. Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends

........................................... 403

19. Hemolytic Disease of the Fetus and Newborn (HDFN) ......................................................................... 427 ........................ 1

20. Autoimmune Hemolytic Anemias ............................................. 439 2. Basic Genetics

.............................................................................................. 26

3. Fundamentals of Immunology ....................................................... 45 4. Concepts in Molecular Biology

Part IV: Leukocyte Antigens and Relationship Testing

..................................................... 77

21. The HLA System

Part II:

22. Relationship Testing

Blood Groups and Serologic Testing 5. The Antiglobulin Test ........................................................................... 101 6. The ABO Blood Group System ..................................................... 119 7. The Rh Blood Group System

....................................................................................... 475 ............................................................................. 495

Part V: Quality and Compliance Issues 23. Quality Management

........................................................................... 509

......................................................... 149

8. Blood Group Terminology and the Other Blood Groups .............................................................................................. 172 9. Detection and Identification of Antibodies ...................... 216 10. Pretransfusion Testing ........................................................................ 241 11. Overview of the Routine Blood Bank Laboratory .................................................................................................... 260 12. Other Technologies and Automation ..................................... 273

24. Utilization Management

................................................................... 526

25. Transfusion Safety and Federal Regulatory Requirements ............................................................................................. 540 26. Laboratory Information Systems

.............................................. 556

27. Medicolegal and Ethical Aspects of Providing Blood Collection and Transfusion Services ....................................... 571

Part VI: Future Trends

Part III:

28. Tissue Banking: A New Role for the Transfusion Service .............................................................................................................. 581

Transfusion Practice 13. Donor Screening and Component Preparation

............ 289

Appendix A:

14. Apheresis ........................................................................................................ 331

Answer Key

15. Transfusion Therapy

Glossary

............................................................................ 352

16. Adverse Effects of Blood Transfusion ................................... 367 17. Cellular Therapy

Index

.............................................................................................................. 601

....................................................................................................................... 613

.............................................................................................................................. 637

...................................................................................... 391

xv

2682_FM_i-xvi 22/05/12 2:12 PM Page xvi

xvi

Contents

Procedures Available on DavisPlus The following procedures can be found on the textbook’s companion website at DavisPlus. RELATED CHAPTER

PROCEDURE

Chapter 5: The Antiglobulin Test

• Procedure 5-1: Direct Antiglobulin Test • Procedure 5-2: Indirect Antiglobulin Test

Chapter 6: The ABO Blood Group System

• Procedure 6-1: Determination of the Secretor Property

Chapter 8: Blood Group Terminology and the Other Blood Groups

• Procedure 8-1: Plasma Inhibition Studies

Chapter 10: Pretransfusion Testing

• Procedure 10-1: Preparation of Washed “Dry” Button of RBCs for Serologic Tests • Procedure 10-2: Model One-Tube-Per-Donor-Unit Crossmatch Procedure • Procedure 10-3: Saline Replacement Procedure

Chapter 20: Autoimmune Hemolytic Anemias

• Procedure 20-1: Use of Thiol Reagents to Disperse Autoagglutination • Procedure 20-2: Cold Autoadsorption • Procedure 20-3: Prewarm Technique for Testing Serum Containing Cold Agglutinins • Procedure 20-4: Adsorption of Cold Autoantibodies with Rabbit Erythrocyte Stroma • Procedure 20-5: Dissociation of IgG by Chloroquine • Procedure 20-6: Digitonin-Acid Elution • Procedure 20-7: Autologous Adsorption of Warm Reactive Autoantibodies Application • Heat and Enzyme Method • ZZAP Method • Procedure 20-8: Demonstration of Drug-Induced Immune Complex Formation • Procedure 20-9: Detection of Antibodies to Penicillin or Cephalothin • Procedure 20-10: EDTA/Glycine Acid (EGA) Method to Remove Antibodies from RBCs • Procedure 20-11: Separation of Transfused from Autologous RBCs by Simple Centrifugation: Reticulocyte Harvesting

Also available at DavisPlus (http://davisplus.fadavis.com/): Polyagglutination, by Phyllis S. Walker, MS, MT(ASCP)SBB.

2682_Ch01_001-025 28/05/12 12:22 PM Page 1

Part I

Fundamental Concepts

Chapter

1

Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends Denise M. Harmening, PhD, MT(ASCP) and Valerie Dietz Polansky, MEd, MLS(ASCP)CM

Introduction Historical Overview Current Status RBC Biology and Preservation RBC Membrane Metabolic Pathways RBC Preservation Anticoagulant Preservative Solutions Additive Solutions Freezing and Rejuvenation Current Trends in RBC Preservation Research Improved Additive Solutions Procedures to Reduce and Inactivate Pathogens Formation of O-Type RBCs Blood Pharming RBC Substitutes

Platelet Preservation The Platelet Storage Lesion Clinical Use of Platelets Current Conditions for Platelet Preservation (Platelet Storage) History of Platelet Storage: Rationale for Current Conditions Storage in Second-Generation Containers Storing Platelets Without Agitation for Limited Times Measurement of Viability and Functional Properties of Stored Platelets Platelet Storage and Bacterial Contamination

Current Trends in Platelet Preservation Research Storage for 7 Days at 20°C to 24°C Storage with Additive Solutions Procedures to Reduce and Inactivate Pathogens Development of Platelet Substitutes New Approaches for Storage of Platelets at 1°C to 6°C Frozen Platelets Summary Chart Review Questions References

OBJECTIVES 1. List the major developments in the history of transfusion medicine. 2. Describe several biological properties of red blood cells (RBC) that can affect post-transfusion survival. 3. Identify the metabolic pathways that are essential for normal RBC function and survival. 4. Define the hemoglobin-oxygen dissociation curve, including how it is related to the delivery of oxygen to tissues by transfused RBCs. 5. Explain how transfusion of stored blood can cause a shift to the left of the hemoglobin-oxygen dissociation curve. 6. State two FDA criteria that are used to evaluate new preservation solutions and storage containers. 7. State the temperature for storage of RBCs in the liquid state. Continued

1

2682_Ch01_001-025 28/05/12 12:22 PM Page 2

2

PART I

Fundamental Concepts

OBJECTIVES—cont’d 8. Define storage lesion and list the associated biochemical changes. 9. Explain the importance of 2,3-DPG levels in transfused blood, including what happens to levels post-transfusion and which factors are involved. 10. Name the approved anticoagulant preservative solutions, explain the function of each ingredient, and state the maximum storage time for RBCs collected in each. 11. Name the additive solutions licensed in the United States, list the common ingredients, and describe the function of each ingredient. 12. Explain how additive solutions are used and list their advantages. 13. Explain rejuvenation of RBCs. 14. List the name and composition of the FDA-approved rejuvenation solution and state the storage time following rejuvenation. 15. Define the platelet storage lesion. 16. Describe the indications for platelet transfusion and the importance of the corrected count increment (CCI). 17. Explain the storage requirements for platelets, including rationale. 18. Explain the swirling phenomenon and its significance. 19. List the two major reasons why platelet storage is limited to 5 days in the United States. 20. List the various ways that blood banks in the United States meet AABB Standard 5.1.5.1: “The blood bank or transfusion service shall have methods to limit and to detect or inactivate bacteria in all platelet components.” 21. Explain the use and advantages of platelet additive solutions (PASs), and name one that is approved for use in the United States.

Introduction People have always been fascinated by blood: Ancient Egyptians bathed in it, aristocrats drank it, authors and playwrights used it as themes, and modern humanity transfuses it. The road to an efficient, safe, and uncomplicated transfusion technique has been rather difficult, but great progress has been made. This chapter reviews the historical events leading to the current status of how blood is stored. A review of RBC biology serves as a building block for the discussion of red cell preservation, and a brief description of platelet metabolism sets the stage for reviewing the platelet storage lesion. Current trends in red cell and platelet preservation research are presented for the inquisitive reader.

Historical Overview In 1492, blood was taken from three young men and given to the stricken Pope Innocent VII in the hope of curing him; unfortunately, all four died. Although the outcome of this event was unsatisfactory, it is the first time a blood transfusion was recorded in history. The path to successful transfusions that is so familiar today is marred by many reported failures, but our physical, spiritual, and emotional fascination with blood is primordial. Why did success elude experimenters for so long? Clotting was the principal obstacle to overcome. Attempts to find a nontoxic anticoagulant began in 1869, when Braxton Hicks recommended sodium phosphate. This was perhaps the first example of blood preservation research. Karl Landsteiner in 1901 discovered the ABO blood groups and explained the serious reactions that occur in humans as

a result of incompatible transfusions. His work early in the 20th century won a Nobel Prize. Next came devices designed for performing the transfusions. Edward E. Lindemann was the first to succeed. He carried out vein-to-vein transfusion of blood by using multiple syringes and a special cannula for puncturing the vein through the skin. However, this time-consuming, complicated procedure required many skilled assistants. It was not until Unger designed his syringe-valve apparatus that transfusions from donor to patient by an unassisted physician became practical. An unprecedented accomplishment in blood transfusion was achieved in 1914, when Hustin reported the use of sodium citrate as an anticoagulant solution for transfusions. Later, in 1915, Lewisohn determined the minimum amount of citrate needed for anticoagulation and demonstrated its nontoxicity in small amounts. Transfusions became more practical and safer for the patient. The development of preservative solutions to enhance the metabolism of the RBC followed. Glucose was tried as early as 1916, when Rous and Turner introduced a citrate-dextrose solution for the preservation of blood. However, the function of glucose in RBC metabolism was not understood until the 1930s. Therefore, the common practice of using glucose in the preservative solution was delayed. World War II stimulated blood preservation research because the demand for blood and plasma increased. The pioneer work of Dr. Charles Drew during World War II on developing techniques in blood transfusion and blood preservation led to the establishment of a widespread system of blood banks. In February 1941, Dr. Drew was appointed director of the first American Red Cross blood bank at Presbyterian Hospital. The pilot

2682_Ch01_001-025 28/05/12 12:22 PM Page 3

Chapter 1 Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends

program Dr. Drew established became the model for the national volunteer blood donor program of the American Red Cross.1 In 1943, Loutit and Mollison of England introduced the formula for the preservative acid-citrate-dextrose (ACD). Efforts in several countries resulted in the landmark publication of the July 1947 issue of the Journal of Clinical Investigation, which devoted nearly a dozen papers to blood preservation. Hospitals responded immediately, and in 1947, blood banks were established in many major cities of the United States; subsequently, transfusion became commonplace. The daily occurrence of transfusions led to the discovery of numerous blood group systems. Antibody identification surged to the forefront as sophisticated techniques were developed. The interested student can review historic events during World War II in Kendrick’s Blood Program in World War II, Historical Note.2 In 1957, Gibson introduced an improved preservative solution called citratephosphate-dextrose (CPD), which was less acidic and eventually replaced ACD as the standard preservative used for blood storage. Frequent transfusions and the massive use of blood soon resulted in new problems, such as circulatory overload. Component therapy has solved these problems. Before, a single unit of whole blood could serve only one patient. With component therapy, however, one unit may be used for multiple transfusions. Today, physicians can select the specific component for their patient’s particular needs without risking the inherent hazards of whole blood transfusions. Physicians can transfuse only the required fraction in the concentrated form, without overloading the circulation. Appropriate blood component therapy now provides more effective treatment and more complete use of blood products (see Chapter 13, “Donor Screening and Component Preparation”). Extensive use of blood during this period, coupled with component separation, led to increased comprehension of erythrocyte metabolism and a new awareness of the problems associated with RBC storage.

Current Status AABB, formerly the American Association of Blood Banks, estimates that there were 19 million volunteer donors in 2008.3 Based on the 2009 National Blood Collection and Utilization Survey Report, about 17 million units of whole blood and RBCs were donated in 2008 in the United States.3 Approximately 24 million blood components were transfused in 2008.3 With an aging population and advances in medical treatments requiring transfusions, the demand for blood and blood components can be expected to continue to increase.3 The New York Blood Center estimates that one in three people will need blood at some point in their lifetime.4 These units are donated by fewer than 10% of healthy Americans who are eligible to donate each year, primarily through blood drives conducted at their place of work. Individuals can also donate at community blood centers (which collect approximately 88% of the nation’s blood) or hospital-based donor centers (which collect approximately 12% of the nation’s blood supply). Volunteer donors are not

3

paid and provide nearly all of the blood used for transfusion in the United States. Traditionally, the amount of whole blood in a unit has been 450 mL +/–10% of blood (1 pint). More recently, 500 mL +/–10% of blood are being collected. This has provided a small increase in the various components. Modified plastic collection systems are used when collecting 500 mL of blood, with the volume of anticoagulant-preservative solution being increased from 63 mL to 70 mL. For a 110-pound donor, a maximum volume of 525 mL can be collected, including samples drawn for processing.5 The total blood volume of most adults is 10 to 12 pints, and donors can replenish the fluid lost from the 1-pint donation in 24 hours. The donor’s red cells are replaced within 1 to 2 months after donation. A volunteer donor can donate whole blood every 8 weeks. Units of the whole blood collected can be separated into three components: packed RBCs, platelets, and plasma. In recent years, less whole blood has been used to prepare platelets with the increased utilization of apheresis platelets. Hence, many units are converted only into RBCs and plasma. The plasma can be converted by cryoprecipitation to a clotting factor concentrate that is rich in antihemophilic factor (AHF, factor VIII; refer to Chapter 13). A unit of whole blood–prepared RBCs may be stored for 21 to 42 days, depending on the anticoagulant-preservative solution used when the whole blood unit was collected, and whether a preserving solution is added to the separated RBCs. Although most people assume that donated blood is free because most blood-collecting organizations are nonprofit, a fee is still charged for each unit to cover the costs associated with collecting, storing, testing, and transfusing blood. The donation process consists of three steps or processes (Box 1–1): 1. Educational reading materials 2. The donor health history questionnaire 3. The abbreviated physical examination

BOX 1–1

The Donation Process Step 1: Educational Materials Educational material (such as the AABB pamphlet “An Important Message to All Blood Donors”) that contains information on the risks of infectious diseases transmitted by blood transfusion, including the symptoms and sign of AIDS, is given to each prospective donor to read. Step 2: The Donor Health History Questionnaire A uniform donor history questionnaire, designed to ask questions that protect the health of both the donor and the recipient, is given to every donor. The health history questionnaire is used to identify donors who have been exposed to diseases that can be transmitted in blood (e.g., variant Creutzfeldt-Jakob, West Nile virus, malaria, babesiosis, or Chagas disease). Step 3: The Abbreviated Physical Examination The abbreviated physical examination for donors includes blood pressure, pulse, and temperature readings; hemoglobin or hematocrit level; and the inspection of the arms for skin lesions.

2682_Ch01_001-025 28/05/12 12:22 PM Page 4

4

PART I

Fundamental Concepts

The donation process, especially steps 1 and 2, has been carefully modified over time to allow for the rejection of donors who may transmit transfusion-associated disease to recipients. For a more detailed description of donor screening and processing, refer to Chapter 13. The nation’s blood supply is safer than it has ever been because of the donation process and extensive laboratory screening (testing) of blood. Currently, 10 screening tests for infectious disease are performed on each unit of donated blood (Table 1–1). The current risk of transfusion-transmitted hepatitis C virus (HCV) is 1 in 1,390,000, and for hepatitis B virus (HBV), it is between 1 in 200,000 and 1 in 500,000, respectively.6,7 The use of nucleic acid amplification testing (NAT), licensed by the Food and Drug Administration (FDA) since 2002, is one reason for the increased safety of the blood supply. Refer to Chapter 18, “Transfusion-Transmitted Diseases” for a detailed discussion of transfusion-transmitted viruses.

RBC Biology and Preservation Three areas of RBC biology are crucial for normal erythrocyte survival and function: 1. Normal chemical composition and structure of the RBC membrane 2. Hemoglobin structure and function 3. RBC metabolism Defects in any or all of these areas will result in RBCs surviving less than the normal 120 days in circulation.

Table 1–1 Current Donor Screening Tests for Infectious Diseases TEST

DATE TEST REQUIRED

Syphilis

1950s

Hepatitis B surface antigen (HBsAg)

1971

Hepatitis B core antibody (anti-HBc)

1986

Hepatitis C virus antibody (anti-HCV)

1990

Human immunodeficiency virus antibodies (anti-HIV-1/2)

19921

Human T-cell lymphotropic virus antibody (anti-HTLV-I/II)

19972

Human immunodeficiency virus (HIV-1)(NAT)*,**

1999

Hepatitis C virus (HCV) (NAT) **

1999

West Nile virus (NAT)

2004

Trypanosoma cruzi antibody (anti-T. cruzi)

2007

*NAT-nucleic acid amplification testing **Initially under IND starting in 1999 1 Anti-HIV-1 testing implemented in 1985 2 Anti-HTLV testing implemented in 1988

RBC Membrane Basic Concepts The RBC membrane represents a semipermeable lipid bilayer supported by a meshlike protein cytoskeleton structure (Fig. 1–1).8 Phospholipids, the main lipid components of the membrane, are arranged in a bilayer structure comprising the framework in which globular proteins traverse and move. Proteins that extend from the outer surface and span the entire membrane to the inner cytoplasmic side of the RBC are termed integral membrane proteins. Beneath the lipid bilayer, a second class of membrane proteins, called peripheral proteins, is located and limited to the cytoplasmic surface of the membrane forming the RBC cytoskeleton.8

Advanced Concepts Both proteins and lipids are organized asymmetrically within the RBC membrane. Lipids are not equally distributed in the two layers of the membrane. The external layer is rich in glycolipids and choline phospholipids.9 The internal cytoplasmic layer of the membrane is rich in amino phospholipids.9 The biochemical composition of the RBC membrane is approximately 52% protein, 40% lipid, and 8% carbohydrate.10 As mentioned previously, the normal chemical composition and the structural arrangement and molecular interactions of the erythrocyte membrane are crucial to the normal length of RBC survival of 120 days in circulation. In addition, they maintain a critical role in two important RBC characteristics: deformability and permeability. Deformability To remain viable, normal RBCs must also remain flexible, deformable, and permeable. The loss of adenosine triphosphate (ATP) (energy) levels leads to a decrease in the phosphorylation of spectrin and, in turn, a loss of membrane deformability.9 An accumulation or increase in deposition of membrane calcium also results, causing an increase in membrane rigidity and loss of pliability. These cells are at a marked disadvantage when they pass through the small (3 to 5 µm in diameter) sinusoidal orifices of the spleen, an organ that functions in extravascular sequestration and removal of aged, damaged, or less deformable RBCs or fragments of their membrane. The loss of RBC membrane is exemplified by the formation of “spherocytes” (cells with a reduced surface-to-volume ratio; Fig. 1–2) and “bite cells,” in which the removal of a portion of membrane has left a permanent indentation in the remaining cell membrane (Fig. 1–3). The survival of these forms is also shortened. Permeability The permeability properties of the RBC membrane and the active RBC cation transport prevent colloid hemolysis and control the volume of the RBC. Any abnormality that increases permeability or alters cationic transport may decrease RBC survival. The RBC membrane is freely permeable to

2682_Ch01_001-025 28/05/12 12:22 PM Page 5

Chapter 1 Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends I = integral proteins P = peripheral proteins

Spectrin ankyrin-band 3 interaction

Phospholipids Fatty acid chains

Membrane surface

GP-C

F-actin

5

I I

I

I GP-B

3

3

Lipid bilayer

GP-A

7 P P

2.1 4.2 P

Adducin Protein 4.1 Alpha chain SpectrinBeta chain actin-4.1-adducin Spectrin interaction

6

Ankyrin

P

Membrane cytoskeleton Spectrin dimer-dimer interaction

Figure 1–1. Schematic illustration of red blood cell membrane depicting the composition and arrangement of RBC membrane proteins. GP-A = glycophorin A; GP-B = glycophorin B; GP-C = glycophorin C; G = globin. Numbers refer to pattern of migration of SDS (sodium dodecyl sulfate) polyacrylamide gel pattern stained with Coomassie brilliant blue. Relations of protein to each other and to lipids are purely hypothetical; however, the positions of the proteins relative to the inside or outside of the lipid bilayer are accurate. (Note: Proteins are not drawn to scale and many minor proteins are omitted.) (Reprinted with permission from Harmening, DH: Clinical Hematology and Fundamentals of Hemostasis, 5th ed., FA Davis, Philadelphia, 2009.)

Figure 1–2. Spherocytes.

water and anions. Chloride (Cl–) and bicarbonate (HCO3–) can traverse the membrane in less than a second. It is speculated that this massive exchange of ions occurs through a large number of exchange channels located in the RBC membrane. The RBC membrane is relatively impermeable to cations such as sodium (Na+) and potassium (K+). RBC volume and water homeostasis are maintained by controlling the intracellular concentrations of sodium and potassium. The erythrocyte intracellular-to-extracellular ratios for Na+ and K+ are 1:12 and 25:1, respectively. The 300 cationic pumps, which actively transport Na+ out of the cell and K+ into the cell, require energy in the form of ATP. Calcium (Ca2+) is also actively pumped from the interior of the RBC through energy-dependent calcium-ATPase pumps. Calmodulin, a cytoplasmic calcium-binding protein, is speculated to control these pumps and to prevent excessive intracellular Ca2+ buildup, which changes the

Figure 1–3. “Bite” cells.

shape and makes it more rigid. When RBCs are ATPdepleted, Ca2+ and Na+ are allowed to accumulate intracellularly, and K+ and water are lost, resulting in a dehydrated rigid cell subsequently sequestered by the spleen, resulting in a decrease in RBC survival.

Metabolic Pathways Basic Concepts The RBC’s metabolic pathways that produce ATP are mainly anaerobic, because the function of the RBC is to deliver oxygen, not to consume it. Because the mature erythrocyte has no nucleus and there is no mitochondrial apparatus for oxidative metabolism, energy must be generated almost exclusively through the breakdown of glucose.

2682_Ch01_001-025 28/05/12 12:22 PM Page 6

6

PART I

Fundamental Concepts

Advanced Concepts RBC metabolism may be divided into the anaerobic glycolytic pathway and three ancillary pathways that serve to maintain the structure and function of hemoglobin (Fig. 1–4): the pentose phosphate pathway, the methemoglobin reductase pathway, and the Luebering-Rapoport shunt. All of these processes are essential if the erythrocyte is to transport oxygen and to maintain critical physical characteristics for its survival. Glycolysis generates about 90% of the ATP needed by the RBC. Approximately 10% is provided by the pentose phosphate pathway. The methemoglobin reductase pathway is another important pathway of RBC metabolism, and a defect can affect RBC post-transfusion survival and function. Another pathway that is crucial to RBC function is the Luebering-Rapoport shunt. This pathway permits the accumulation of an important RBC organic phosphate, 2,3-diphosphoglycerate (2,3-DPG). The amount of 2,3-DPG found within RBCs has a significant effect on the affinity of hemoglobin for oxygen and therefore affects how well RBCs function post-transfusion.

Hemoglobin Oxygen Dissociation Curve Hemoglobin’s primary function is gas transport: oxygen delivery to the tissues and carbon dioxide (CO2) excretion. One of the most important controls of hemoglobin affinity for oxygen is the RBC organic phosphate 2, 3-DPG. The unloading of oxygen by hemoglobin is accompanied by widening of a space between ␤ chains and the binding of 2,3-DPG on a mole-for-mole basis, with the formation of anionic salt bridges between the chains. The resulting conformation of the deoxyhemoglobin molecule is known as the tense (T) form, which has a lower affinity for oxygen. When hemoglobin loads oxygen and becomes oxyhemoglobin, the established salt bridges are broken, and ␤ chains are pulled together, expelling 2,3-DPG. This is the relaxed (R) form of the hemoglobin molecule, which has a higher affinity for oxygen. These allosteric changes that occur as the hemoglobin loads and unloads oxygen are referred to as the respiratory movement. The dissociation and binding of oxygen by hemoglobin are not directly proportional to the partial pressure of oxygen (pO2) in its environment

PHOSPHOGLUCONATE PATHWAY (oxidative) H2O2 EMBDEN-MEYERHOF PATHWAY (non-oxidative)

GSH

GSSG GR

Glucose ATP ADP

GP

HK

NADP

NADPH 6-P-Gluconate G-6-PD 6-PGD CO2

Glucose 6-P GPI Fructose 6-P ATP ADP METHEMOGLOBIN REDUCTASE PATHWAY Hemoglobin R Methemoglobin HK GPI PFK A TPI GAPD PGM E PK LDH DPGM DPGP G-6-PD 6-PGD GR GP DHAP PGK R

Hexokinase Glucose-6-phosphate isomerase Phosphofructokinase Aldolase Triose phosphate isomerase Glyceraldehyde-3-phosphate dehydrogenase Phosphoglycerate mutase Enolase Pyruvate kinase Lactic dehydrogenase Diphosphoglyceromutase Diphosphoglycerate phosphatase Glucose-6-phosphate dehydrogenase 6-Phosphogluconate dehydrogenase Glutathione reductase Glutathione peroxidase Dihydroxyacetone-P Phosphoglycerate kinase NADH-methemoglobin reductase

Fructose 1,6-diP A Glyceraldehyde

NAD NADH

Pentose-P

PFK

DHAP

GAPD 1,3-diP-Glycerate

ADP ATP

PGK

LUEBERING-RAPAPORT PATHWAY DPGM 2,3-diP-Glycerate DPGP

3-P-Glycerate PGM 2-P-Glycerate E P-Enolpyruvate ADP ATP

PK Pyruvate

NADH NAD

LDH Lactate

Figure 1–4. Red cell metabolism. (Reprinted with permission from Hillman, RF, and Finch, CA: Red Cell Manual, 7th ed., FA Davis, Philadelphia, 1996.)

2682_Ch01_001-025 28/05/12 12:22 PM Page 7

Chapter 1 Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends

but instead exhibit a sigmoid-curve relationship, known as the hemoglobin-oxygen dissociation curve (Fig. 1–5). The shape of this curve is very important physiologically because it permits a considerable amount of oxygen to be delivered to the tissues with a small drop in oxygen tension. For example, in the environment of the lungs, where the oxygen (pO2) tension, measured in millimeters of mercury (mm Hg), is nearly 100 mm Hg, the hemoglobin molecule is almost 100% saturated with oxygen. As the RBCs travel to the tissues, where the (pO2) drops to an average of 40 mm Hg (mean venous oxygen tension), the hemoglobin saturation drops to approximately 75% saturation, releasing about 25% of the oxygen to the tissues. This is the normal situation of oxygen delivery at a basal metabolic rate. The normal position of the oxygen dissociation curve depends on three different ligands normally found within the RBC: H+ ions, CO2, and organic phosphates. Of these three ligands, 2,3-DPG plays the most important physiological role. Normal hemoglobin function depends on adequate 2, 3-DPG levels in the RBC. In situations such as hypoxia, a compensatory shift to the right of the hemoglobin-oxygen dissociation curve alleviates the tissue oxygen deficit. This rightward shift of the curve, mediated by increased levels of 2,3-DPG, decreases hemoglobin’s affinity for the oxygen molecule and increases oxygen delivery to the tissues. A shift to the left of the hemoglobin-oxygen dissociation curve results, conversely, in an increase in hemoglobinoxygen affinity and a decrease in oxygen delivery to the tissues. With such a dissociation curve, RBCs are much less efficient because only 12% of the oxygen can be released to the tissues. Multiple transfusions of 2,3-DPG– depleted stored blood can shift the oxygen dissociation curve to the left.11

100

Oxyhemoglobin (% saturation)

RBC Preservation Basic Concepts The goal of blood preservation is to provide viable and functional blood components for patients requiring blood transfusion. RBC viability is a measure of in vivo RBC survival following transfusion. Because blood must be stored from the time of donation until the time of transfusion, the viability of RBCs must be maintained during the storage time as well. The FDA requires an average 24-hour post-transfusion RBC survival of more than 75%.12 In addition, the FDA mandates that red cell integrity be maintained throughout the shelf-life of the stored RBCs. This is assessed as free hemoglobin less than 1% of total hemoglobin.13 These two criteria are used to evaluate new preservation solutions and storage containers. To determine post-transfusion RBC survival, RBCs are taken from healthy subjects, stored, and then labeled with radioisotopes, reinfused to the original donor, and measured 24 hours after transfusion. Despite FDA requirements, the 24-hour post-transfusion RBC survival at outdate can be less than 75%;12,14 and in critically ill patients is often less than 75%.14,15 To maintain optimum viability, blood is stored in the liquid state between 1°C and 6°C for a specific number of days, as determined by the preservative solution(s) used. The loss of RBC viability has been correlated with the lesion of storage, which is associated with various biochemical changes (Table 1–2).

Advanced Concepts Because low 2,3-DPG levels profoundly influence the oxygen dissociation curve of hemoglobin,16 DPG-depleted RBCs may have an impaired capacity to deliver oxygen to the tissues. As RBCs (in whole blood or RBC concentrates)

Normal “Left-shifted”

90

“Right-shifted”

80

↑Abn Hb ↑pH ↓DPG ↓Temp ↓P50

Table 1–2 RBC Storage Lesion CHARACTERISTIC

CHANGE OBSERVED

% Viable cells

Decreased

Glucose

Decreased

40

ATP

Decreased

30

Lactic acid

Increased

20

pH

Decreased

2,3-DPG

Decreased

Oxygen dissociation curve

Shift to the left (increase in hemoglobin and oxygen affinity; less oxygen delivered to tissues)

Plasma K+

Increased

Plasma hemoglobin

Increased

70 60 50

↓pH ↑DPG ↑Temp ↑P50

P50

10 Normal P50 = 28 mm Hg 0 0

10

20

30

40

50

60

70

80

90 100

PO2 (mm Hg) Figure 1–5. Hemoglobin-oxygen dissociation curve. (Reprinted with permission from Harmening, DH: Clinical Hematology and Fundamentals of Hemostasis, 5th ed., FA Davis, Philadelphia, 2009.)

7

2682_Ch01_001-025 28/05/12 12:22 PM Page 8

8

PART I

Fundamental Concepts

are stored, 2,3-DPG levels decrease, with a shift to the left of the hemoglobin-oxygen dissociation curve, and less oxygen is delivered to the tissues. It is well accepted, however, that 2,3-DPG is re-formed in stored RBCs, after in vivo circulation, resulting in restored oxygen delivery. The rate of restoration of 2,3-DPG is influenced by the acid-base status of the recipient, the phosphorus metabolism, the degree of anemia, and the overall severity of the disorder.11 It has been reported that within the first hour after transfusion, most RBC clearance occurs.14 Approximately 220 to 250 mg of iron are contained in one RBC unit.17 Therefore, rapid RBC clearance of even 25% of a single unit of blood delivers a massive load of hemoglobin iron to the monocyte and macrophage system, producing harmful effects.13

Anticoagulant Preservative Solutions Basic Concepts Table 1–3 lists the approved anticoagulant preservative solutions for whole blood and RBC storage at 1°C to 6°C. The addition of various chemicals, along with the approved anticoagulant-preservative CPD, was incorporated in an attempt to stimulate glycolysis so that ATP levels were better maintained.18 One of the chemicals, adenine, incorporated into the CPD solution (CPDA-1) increases ADP levels, thereby driving glycolysis toward the synthesis of ATP. CPDA-1 contains 0.25 mM of adenine plus 25% more glucose than CPD. Adenine-supplemented blood can be stored at 1°C to 6°C for 35 days; the other anticoagulants are approved for 21 days. Table 1–4 lists the various chemicals used in anticoagulant solutions and their functions during the storage of red cells.

Advanced Concepts It is interesting to note that blood stored in all CPD preservatives also becomes depleted of 2,3-DPG by the second week of storage. The reported pathophysiological effects of

Table 1–3 Approved Anticoagulant Preservative Solutions ABBREVIATION

STORAGE TIME (DAYS)

Acid citrate-dextrose (formula A) *

ACD-A

21

Citrate-phosphate dextrose

CPD

21

Citrate-phosphatedouble-dextrose

CP2D

21

Citrate-phosphatedextrose-adenine

CPDA-1

35

NAME

* ACD-A is used for apheresis components.

the transfusion of RBCs with low 2,3-DPG levels and increased affinity for oxygen include: an increase in cardiac output, a decrease in mixed venous (pO2) tension, or a combination of these.11 The physiological importance of these effects is not easily demonstrated. This is a complex mechanism with numerous variables involved that are beyond the scope of this text. Stored RBCs do regain the ability to synthesize 2,3-DPG after transfusion, but levels necessary for optimal hemoglobin oxygen delivery are not reached immediately. Approximately 24 hours are required to restore normal levels of 2,3-DPG after transfusion.19 The 2,3-DPG concentrations after transfusion have been reported to reach normal levels as early as 6 hours post-transfusion.19 Most of these studies have been performed on normal, healthy individuals. However, evidence suggests that, in the transfused subject whose capacity is limited by an underlying physiological disturbance, even a brief period of altered oxygen hemoglobin affinity is of great significance.14 It is quite clear now that 2,3-DPG levels in transfused blood are important in certain clinical conditions. Studies demonstrate that myocardial function improves following transfusion of blood with high 2,3-DPG levels during cardiovascular surgery.11 Several investigators suggest that the patient in shock who is given 2,3-DPG–depleted erythrocytes in transfusion may have already strained the compensatory mechanisms to their limits.11,20–22 Perhaps for this type of patient, the poor oxygen delivery capacity of 2,3-DPG–depleted cells makes a significant difference in recovery and survival. It is apparent that many factors may limit the viability of transfused RBCs. One of these factors is the plastic material used for the storage container. The plastic must be sufficiently permeable to CO2 in order to maintain higher pH levels during storage. Glass storage containers are a matter of history in the United States. Currently, the majority of blood is stored in polyvinyl chloride (PVC) plastic bags. One issue associated with PVC bags relates to the plasticizer di(ethylhexyl)-phthalate (DEHP), which is used in the manufacture of the bags. It has been found to leach from the plastic into the lipids of the plasma medium and RBC membranes of the blood during storage. However, its use or that of alternative plasticizers that leach are important because they have been shown to stabilize the RBC membrane and therefore reduce the extent of hemolysis during storage. Another issue with PVC is its tendency to break at low temperatures; therefore, components frozen in PVC bags must be handled with care. In addition to PVC, polyolefin containers, which do not contain DEHP, are available for some components, and latex-free plastic containers are available for recipients with latex allergies.5

Additive Solutions Basic Concepts Additive solutions (AS) are preserving solutions that are added to the RBCs after removal of the plasma with or

2682_Ch01_001-025 28/05/12 12:22 PM Page 9

Chapter 1 Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends

9

Table 1–4 Chemicals in Anticoagulant Solutions CHEMICAL

FUNCTION

PRESENT IN ACD-A

CPD

CP2D

CPDA-1

Citrate (sodium citrate/citric acid)

Chelates calcium; prevents clotting

X

X

X

X

Monobasic sodium phosphate

Maintains pH during storage; necessary for maintenance of adequate levels of 2,3-DPG

X

X

X

X

Dextrose

Substrate for ATP production (cellular energy)

X

X

X

X

Adenine

Production of ATP (extends shelf-life from 21 to 35 days)

X

ACD-A = Acid citrate-dextrose (formula A); CPD = Citrate-phosphate dextrose; CP2D = Citrate phosphate double dextrose; CPDA-1 = Citrate phosphate dextrose adenine; 2,3-DPG = 2,3-diphosphoglycerate; ATP = adenosine triphosphate

without platelets. Additive solutions are now widely used. One of the reasons for their development is that removal of the plasma component during the preparation of RBC concentrates removed much of the nutrients needed to maintain RBCs during storage. This was dramatically observed when high-hematocrit RBCs were prepared. The influence of removing substantial amounts of adenine and glucose present originally in, for example, the CPDA-1 anticoagulant-preservative solution led to a decrease in viability, particularly in the last 2 weeks of storage.14 RBC concentrates prepared from whole blood units collected in primary anticoagulant-preservative solutions can be relatively void of plasma with high hematocrits, which causes the units to be more viscous and difficult to infuse, especially in emergency situations. Additive solutions (100 mL to the RBC concentrate prepared from a 450-mL blood collection) also overcome this problem. Additive solutions reduce hematocrits from around 70% to 85% to around 50% to 60%. The ability to pack RBCs to fairly high hematocrits before adding additive solution, also provides a means to harvest greater amounts of plasma with or without platelets. Box 1–2 summarizes the benefits of RBC additive solutions. Currently, three additive solutions are licensed in the United States: 1. Adsol (AS-1; Baxter Healthcare) 2. Nutricel (AS-3; Pall Corporation) 3. Optisol (AS-5; Terumo Corporation) The additive solution is contained in a satellite bag and is added to the RBCs after most of the plasma has been expressed. All three additives contain saline, adenine, and

glucose. AS-1 and AS-5 also contain mannitol, which protects against storage-related hemolysis,23 while AS-3 contains citrate and phosphate for the same purpose. All of the additive solutions are approved for 42 days of storage for packed RBCs. Table 1–5 lists the currently approved additive solutions.

Advanced Concepts Table 1–6 shows the biochemical characteristics of RBCs stored in the three additive solutions after 42 days of storage.4,24,25 Additive system RBCs are used in the same way

Table 1–5 Additive Solutions in Use in North America ABBREVIATION

STORAGE TIME (DAYS)

Adsol (Baxter Healthcare)

AS-1

42

Nutricel (Pall Corporation)

AS-3

42

Optisol (Terumo Corporation)

AS-5

42

NAME

Table 1–6 Red Cell Additives: Biochemical Characteristics Storage period (days) pH (measured at 37°C)

AS-1

AS-3

AS-5

42

42

42

6.6

6.5

6.5

BOX 1–2

24-hour survival*(%)

83

85.1

80

Benefits of RBC Additive Solutions

ATP (% initial)

68

67

68.5

2,3-DPG (% initial)

6

6

5

0.7

0.6

• Extends the shelf-life of RBCs to 42 days by adding nutrients • Allows for the harvesting of more plasma and platelets from the unit • Produces an RBC concentrate of lower viscosity that is easier to infuse

Hemolysis (%)

0.5

*Survival studies reported are from selected investigators and do not include an average of all reported survivals.

2682_Ch01_001-025 28/05/12 12:22 PM Page 10

10

PART I

Fundamental Concepts

as traditional RBC transfusions. Blood stored in additive solutions is now routinely given to newborn infants and pediatric patients,26 although some clinicians still prefer CPDA-1 RBCs because of their concerns about one or more of the constituents in the additive solutions. None of the additive solutions maintain 2,3-DPG throughout the storage time. As with RBCs stored only with primary anticoagulant preservatives, 2,3-DPG is depleted by the second week of storage.

Freezing and Rejuvenation RBC Freezing

Basic Concepts RBC freezing is primarily used for autologous units and the storage of rare blood types. Autologous transfusion (auto meaning “self”) allows individuals to donate blood for their own use in meeting their needs for blood transfusion (see Chapter 15, “Transfusion Therapy”). The procedure for freezing a unit of packed RBCs is not complicated. Basically, it involves the addition of a cryoprotective agent to RBCs that are less than 6 days old. Glycerol is used most commonly and is added to the RBCs slowly with vigorous shaking, thereby enabling the glycerol to permeate the RBCs. The cells are then rapidly frozen and stored in a freezer. The usual storage temperature is below –65°C, although storage (and freezing) temperature depends on the concentration of glycerol used.16 Two concentrations of glycerol have been used to freeze RBCs: a high-concentration glycerol (40% weight in volume [w/v]) and a low-concentration glycerol (20% w/v) in the final concentration of the cryopreservative.5 Most blood banks that freeze RBCs use the high-concentration glycerol technique. Table 1–7 lists the advantages of the high-concentration glycerol technique in comparison with the low-concentration glycerol technique. See Chapter 13 for a detailed description of the RBC freezing procedure. Currently, the FDA licenses frozen RBCs for a period of 10 years from the date of freezing; that is, frozen RBCs may be stored up to 10 years before thawing and transfusion. Once thawed, these RBCs demonstrate function and viability near those of fresh blood. Experience has shown that 10-year storage periods do not adversely affect viability and function.27 Table 1–8 lists the advantages and disadvantages of RBC freezing.

Advanced Concepts Transfusion of frozen cells must be preceded by a deglycerolization process; otherwise the thawed cells would be accompanied by hypertonic glycerol when infused, and RBC lysis would result. Removal of glycerol is achieved by systematically replacing the cryoprotectant with decreasing

Table 1–7 Advantages of High-Concentration Glycerol Technique Used by Most Blood Banks Over Low-Concentration Glycerol Technique ADVANTAGE

HIGH GLYCEROL

LOW GLYCEROL

1. Initial freezing temperature

–80°C

–196°C

2. Need to control freezing rate

No

Yes

3. Type of freezer

Mechanical

Liquid nitrogen

4. Maximum storage temperature

–65°C

–120°C

5. Shipping requirements

Dry ice

Liquid nitrogen

6. Effect of changes in storage temperature

Can be thawed and refrozen

Critical

concentrations of saline. The usual protocol involves washing with 12% saline, followed by 1.6% saline, with a final wash of 0.2% dextrose in normal saline.5 A commercially available cell-washing system, such as one of those manufactured by several companies, has traditionally been used in the deglycerolizing process. Excessive hemolysis is monitored by noting the hemoglobin concentration of the wash supernatant. Osmolality of the unit should also be monitored to ensure adequate deglycerolization. Traditionally, because a unit of blood is processed in an open system (one in which sterility is broken) to add the glycerol (before freezing) or the saline solutions (for deglycerolization), the outdating period of thawed RBCs stored at 1°C to 6°C has been 24 hours. Generally, RBCs in CPD or CPDA-1 anticoagulant-preservatives or additive solutions are glycerolized and frozen within 6 days of whole blood collection. Red blood cells stored in additive solutions such as AS-1, AS-3, and AS-5 have been frozen up to 42 days after liquid

Table 1–8 Advantages and Disadvantages of RBC Freezing ADVANTAGES

DISADVANTAGES

Long-term storage (10 years)

A time-consuming process

Maintenance of RBC viability and function

Higher cost of equipment and materials

Low residual leukocytes and platelets

Storage requirements (–65°C)

Removal of significant amounts of plasma proteins

Higher cost of product

2682_Ch01_001-025 28/05/12 12:22 PM Page 11

Chapter 1 Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends

storage without rejuvenation. The need to transfuse RBCs within 24 hours of thawing has limited the use of frozen RBCs. Recently, an instrument (ACP 215, Haemonetics) has been developed that allows the glycerolization and deglycerolization processes to be performed under closed system conditions.28 This instrument utilizes a sterile connecting device for connections, in-line 0.22 micron filters to deliver solutions, and a disposable polycarbonate bowl with an external seal to deglycerolize the RBCs. RBCs prepared from 450-mL collections and frozen within 6 days of blood collection with CPDA-1 can be stored after thawing at 1°C to 6°C for up to 15 days when the processing is conducted with the ACP 215 instrument. The deglycerolized cells, prepared using salt solutions as in the traditional procedures, are suspended in the AS-3 additive solution as a final step, which is thought to stabilize the thawed RBCs. These storage conditions are based on the parameters used in a study by Valeri and others that showed that RBC properties were satisfactorily maintained during a 15-day period.28 Further studies will broaden the conditions that can be used to prepare RBCs for subsequent freezing with closed system processing. RBC Rejuvenation

Basic Concepts Rejuvenation of RBCs is the process by which ATP and 2,3-DPG levels are restored or enhanced by metabolic alterations. Currently, Rejuvesol (enCyte Systems) is the only FDAapproved rejuvenation solution sold in the United States. It contains phosphate, inosine, pyruvate, and adenine. Rejuvesol is currently approved for use with CPD, CPDA-1, and CPD/AS-1 RBCs. RBCs stored in the liquid state can be rejuvenated at outdate or up to 3 days after outdate, depending on RBC preservative solutions used. Currently, only RBCs prepared from 450-mL collections can be rejuvenated.

Advanced Concepts Rejuvenation is accomplished by incubating the RBC unit with 50 mL of the rejuvenating solution for 1 hour at 37°C. Following rejuvenation, the RBCs can be washed to remove the rejuvenation solution and transfused within 24 hours. More commonly, they are frozen, then washed in the postfreezing deglycerolization process. Because the process is currently accomplished with an open system, federal regulations require that rejuvenated or frozen RBCs are used within 24 hours of thawing.28 It is possible that rejuvenated RBCs could be processed with the closed system ACP 215 instrument, thereby extending their shelf-life. The rejuvenation process is expensive and timeconsuming; therefore, it is not used often but is invaluable for preserving selected autologous and rare units of blood for later use.

11

Current Trends in RBC Preservation Research Advanced Concepts Research and development in RBC preparation and preservation is being pursued in five directions: 1. Development of improved additive solutions 2. Development of procedures to reduce and inactivate the level of pathogens that may be in RBC units 3. Development of procedures to convert A-, B-, and ABtype RBCs to O-type RBCs 4. Development of methods to produce RBCs through bioengineering (blood pharming) 5. Development of RBC substitutes

Improved Additive Solutions Research is being conducted to develop improved additive solutions for RBC preservation. One reason for this is because longer storage periods could improve the logistics of providing RBCs for clinical use, including increased benefits associated with the use of autologous blood/RBCs.

Procedures to Reduce and Inactivate Pathogens Research is being conducted to develop procedures that would reduce the level of or inactivate residual viruses, bacteria, and parasites in RBC units. One objective is to develop robust procedures that could possibly inactivate unrecognized (unknown) pathogens that may be present, such as the viruses that have emerged in recent years. Although methods to inactivate pathogens in plasma have been used successfully for more than 20 years, pathogen reduction of cellular components has proven more challenging. Two methods that utilize alkylating agents that react with the nucleic acids of pathogens (S-303, Cerus/Baxter; Inactine, Vitex) have been evaluated in clinical trials in the United States. Work with Inactin (PEN110) has been discontinued, but clinical studies with S-303–treated RBCs are currently in progress at two U.S. blood centers. Clinical studies of riboflavin and UV light–treated RBCs are expected.29 Areas of concern that must be addressed before pathogen-reduction and pathogen-inactivation technologies are approved for use in the U.S. are potential toxicity, immunogenicity, cellular function, and cost.

Formation of O-Type RBCs The inadequate supply of O-type RBC units that is periodically encountered can hinder blood centers and hospital blood banks in providing RBCs for specific patients. Research over the last 20 years has been evaluating how the more available A and B type of RBCs can be converted to O-type RBCs. The use of enzymes that remove the carbohydrate moieties of the A and B antigens is the mechanism for forming O-type RBCs. The enzymes are removed by washing after completion of the reaction time. A clinical study

2682_Ch01_001-025 28/05/12 12:22 PM Page 12

12

PART I

Fundamental Concepts

sponsored by ZymeQuest, the company that is developing the technology, has shown that O-type RBCs manufactured from B-type RBCs were effective when transfused to O- and A-type patients in need of RBCs.30

Blood Pharming Creating RBCs in the laboratory (blood pharming) is another area of research that has the potential to increase the amount of blood available for transfusion. In 2008, the Defense Advanced Research Projects Agency (DARPA) awarded a bioengineering company named Arteriocyte a contract to develop a system for producing O-negative RBCs on the battlefield. The company, which uses proprietary technology (NANEX) to turn hematopoietic stem cells (HSC) from umbilical cord into type-O, Rh-negative RBCs, sent its first shipment of the engineered blood to the FDA for evaluation in 2010.31 FDA approval is required before human trials can begin. More recently, cultured RBCs generated from in vitro HSC has been reported that survive in circulation for several weeks.32

RBC Substitutes Scientists have been searching for a substitute for blood for over 150 years.33 After the discovery of blood groups in 1901, human-to-human blood transfusions became safer, but blood substitutes continued to be of interest because of their potential to alleviate shortages of donated blood. In the 1980s, safety concerns about HIV led to renewed interest in finding a substitute for human blood, and more recently, the need for blood on remote battlefields has heightened that interest. The U.S. military is one of the strongest advocates for the development of blood substitutes, which it supports through its own research and partnerships with private sector companies. Today the search continues for a safe and effective oxygen carrier that could eliminate many of the problems associated with blood transfusion, such as the need for refrigeration, limited shelf-life, compatibility, immunogenicity, transmission of infectious agents, and shortages. Box 1–3 lists the potential benefits of artificial oxygen carriers. Since RBC substitutes are drugs, they must go through extensive testing in order to obtain FDA approval. Safety and efficacy must be demonstrated through clinical trials. Table 1–9 outlines the different phases of testing. Current research on blood substitutes is focused on two areas: hemoglobin-based oxygen carriers (HBOCs) and perfluorocarbons (PFCs).34,35 Since the function of these products is to carry and transfer oxygen, just one of the many functions of blood, the term RBC substitutes is preferred to the original term blood substitutes. Recently the terms oxygen therapeutics and artificial oxygen carriers (AOC) have been used to describe the broad clinical applications envisioned for these products. Originally developed to be used in trauma situations such as accidents, combat, and surgery, RBC substitutes have, until now, fallen short of meeting requirements for these applications. Despite years of research, RBC substitutes are still not in routine use today. South Africa, Mexico, and Russia are the only countries where any AOCs

BOX 1–3

Potential Benefits of Artificial Oxygen Carriers • Abundant supply • Readily available for use in prehospital settings, battlefields, and remote locations • Can be stockpiled for emergencies and warfare • No need for typing and crossmatching • Available for immediate infusion • Extended shelf-life (1 to 3 years) • Can be stored at room temperature • Free of blood-borne pathogens • At full oxygen capacity immediately • Do not prime circulating neutrophils, reducing the incidence of multiorgan failure • Can deliver oxygen to tissue that is inaccessible to RBCs • Have been accepted by Jehovah’s Witnesses • Could eventually cost less than units of blood

are approved for clinical use. None have received FDA approval for clinical use in the United States, although specific products have been given to individual patients under compassionate use guidelines. Hemoglobin-Based Oxygen Carriers By 1949, it was established that purified hemoglobin could restore blood volume and deliver oxygen; however, its transfusion resulted in serious side effects, such as vasoconstriction and renal failure. This toxicity was thought to be due to stromal remnants in the hemoglobin solutions.36 Ultrapurified stroma-free hemoglobin (SFH) was developed, but it did not readily deliver oxygen to tissues. This was determined to be due to a loss of 2,3-DPG during processing, which caused a shift to the left of the oxygen dissociation

Table 1–9 Phases of Testing PHASE

DESCRIPTION OF TESTING

Preclinical

In vivo and animal testing

Phase I

Researchers test drug in a small group of people (20 to 80) for the first time to evaluate its safety, determine a safe dosage range, and identify side effects.

Phase II

The drug is given to a larger group of people (100 to 300) to see if it is effective and to further evaluate its safety.

Phase III

The drug is given to large groups of people (1,000 to 3,000) to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug to be used safely.

Phase IV

Post marketing studies to gather additional information about the drug’s risks, benefits, and optimal use.

2682_Ch01_001-025 28/05/12 12:22 PM Page 13

Chapter 1 Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends

curve. Another problem was the product’s short half-life, due to dissociation of the hemoglobin molecule into α and β dimers that were filtered by the kidneys and excreted in the urine.32 Scientists began to look for ways to chemically modify the hemoglobin molecule to overcome these problems. Cross-linking, polymerization, and pegylation produced larger, more stable molecules. This reduced some, but not all, of the adverse effects. To date, four generations of HBOCs have been developed.33 HBOCs have been produced from human, bovine, and recombinant hemoglobin. Bovine hemoglobin has several advantages over human hemoglobin. It has a lower oxygen affinity and better oxygen uploading in ischemic tissues, and its availability is not dependent upon an adequate supply of outdated human RBCs. However, concerns about potential immunogenicity and transmission of prions have been raised.37 Although several HBOCs have progressed to phase II and III clinical trials, currently none have been approved for clinical use in humans in the United States or Europe. Development of several products was terminated following clinical trials in which serious adverse side effects were discovered. Two HBOCs are still in clinical trials in the United States and Europe: Hemopure (OPK Biotech) and Hemospan (Sangart). Hemopure was approved for clinical use in South Africa in 2001 and a related product, Oxyglobin, has been used to treat canine anemia in the United States and Europe since 1998. An interesting side note is that a Spanish cyclist admitted to using Oxyglobin in the 2003 Tour de France. He crashed after experiencing nausea. Table 1–10 summarizes the history and status of several HBOCs.

13

A 2008 meta-analysis of 16 clinical trials involving 3,711 patients and five different HBOCs found a significantly increased risk of death and myocardial infarction associated with the use of HBOCs.38 These findings make their widespread clinical use unlikely in the near future; however, some experts believe that HBOCs hold more promise than PFCs.33,39 Table 1–11 lists the advantages and disadvantages of HBOCs. Perfluorocarbons Perfluorocarbons (PFCs) are synthetic hydrocarbon structures in which all the hydrogen atoms have been replaced with fluorine. They are chemically inert, are excellent gas solvents, and carry O2 and CO2 by dissolving them. Because of their small size (about 0.2 microns in diameter), they are able to pass through areas of vasoconstriction and deliver oxygen to tissues that are inaccessible to RBCs. PFCs have been under investigation as possible RBC substitutes since the 1970s. Fluosol (Green Cross Corp.) was approved by the FDA in 1989 but was removed from the market in 1994 due to clinical shortcomings and poor sales. Four other PFCs have proceeded to clinical trials. One, Perftoran (Perftoran), is in clinical use in Russia and Mexico. Two others are no longer under development, and one (Oxycyte, Oxygen Biotherapeutics) is currently being investigated as an oxygen therapeutic for treatment of wounds, decompression sickness, and traumatic brain injury.40 Refer to Table 1–12 for further details, and review of PFCs. Table 1–13 for the advantages and disadvantages of Perfluorochemicals.

Table 1–10 Hemoglobin-Based Oxygen Carriers PRODUCT

MANUFACTURER

CHEMISTRY/SOURCE

HISTORY/STATUS

HemAssist (DCLHb)

Baxter

Diaspirin cross-linked Hgb from outdated human RBCs

First HBOC to advance to phase III clinical trials in United States. Removed from production because of increased mortality rates.

PolyHeme (SFH-P)

Northfield Laboratories

Polymerized and pyridoxalated human Hgb

Underwent phase II/III clinical trials in United States. Did not obtain FDA approval. No longer produced.

Hemopure (HBOC-201)

Originally Biopure; currently OPK Biotech

Polymerized bovine Hgb

Still in phase II/III clinical trials in United States and Europe. Approved for use in S. Africa (2001).

Oxyglobin

Originally Biopure; now OPK Biotech

Polymerized bovine Hgb

Approved for veterinary use in United States and Europe.

Hemospan (MP4)

Sangart

Polyethylene glycol (PEG) attached to the surface of Hgb from human RBCs

In phase II trials in United States; phase III in Europe.

HemoLink

Hemosol

Purified human Hgb from outdated RBCs, cross-linked and polymerized

Abandoned due to cardiac toxicity.

HemoTech

HemoBioTech

Derived from bovine Hgb

Limited clinical trial outside of United States.

Oxy-0301

Oxygenix

Liposome-encapsulated hemoglobin

In experimental phase.

2682_Ch01_001-025 28/05/12 12:22 PM Page 14

14

PART I

Fundamental Concepts

Table 1–11 Advantages and Disadvantages of Hemoglobin-Based Oxygen Carriers ADVANTAGES

DISADVANTAGES

Long shelf-life

Short intravascular half-life

Very stable

Possible toxicity

No antigenicity (unless bovine)

Increased O2 affinity

No requirement for blood-typing procedures

Increased oncotic effect

Table 1–13 Advantages and Disadvantages of Perfluorochemicals ADVANTAGES

DISADVANTAGES

Biological inertness

Adverse clinical effects

Lack of immunogenicity

High O2 affinity

Easily synthesized

Retention in tissues Requirement for O2 administration when infused Deep-freeze storage temperatures

Platelet Preservation Basic Concepts Platelets are intimately involved in primary hemostasis, which is the interaction of platelets and the vascular endothelium in halting and preventing bleeding following vascular injury. Platelets are cellular fragments derived from the cytoplasm of megakaryocytes present in the bone marrow. They do not contain a nucleus, although the mitochondria contain DNA. Platelets are released and circulate approximately 9 to 12 days as small, disk-shaped cells with an average diameter of 2 to 4 µm. The normal platelet count ranges from 150,000 to 350,000 per µL. Approximately 30% of the platelets, that have been released from the bone marrow into the circulation, are sequestered in the microvasculature of the spleen as functional reserves. Platelets have specific roles in the hemostatic process that are critically dependent on an adequate number in the circulation and on normal platelet function. Normal platelet function in vivo requires more than 100,000 platelets per microliter. Spontaneous hemorrhage may occur when the platelet count falls below 10,000. Assuming normal platelet function, a platelet count greater than 50,000/µL will minimize the chance of hemorrhage during surgery.8 The role of platelets in hemostasis includes (1) initial arrest of bleeding by platelet plug formation and

(2) stabilization of the hemostatic plug by contributing to the process of fibrin formation and (3) maintenance of vascular integrity. Platelet plug formation involves the adhesion of platelets to the subendothelium and subsequent aggregation, with thrombin being a key effector of these phenomena. Platelets, like other cells, require energy in the form of ATP for cellular movement, active transport of molecules across the membrane, biosynthetic purposes, and maintenance of a hemostatic steady state.

Advanced Concepts The organelle region of the platelet is responsible for the metabolic activities in this cell. Like many other cells, platelets possess mitochondria and various cytoplasmic granules. Platelets, however, are anucleated and do not possess either a Golgi body or rough endoplasmic reticulum (RER). Generally, the most numerous organelles are the platelet granules. Platelets contain three morphologically distinct types of storage granules: dense granules, α granules, and lysosomes. The α granules are the most numerous (20 to 200 per platelet) and store a number of different substances, such as beta-thromboglobulin (β-TG), platelet factor 4 (PF4), platelet-derived growth factor (PDGF), thrombospondin, and factor V.

Table 1–12 Perfluorocarbons Fluosol-DA

Green Cross Corporation

The only oxygen therapeutic approved for human clinical use in the United States. Approved in 1989; discontinued in 1994 because of clinical shortcomings and poor sales.

Oxygent

Alliance Pharmaceutical Corporation

Phase III trial in Europe completed; phase III trial in United States terminated due to adverse effects. Development stopped due to lack of funding.

Oxyfluor

HemaGen

Early phase clinical trials completed. Development stopped due to loss of financial backing.

Oxycyte

Originally Synthetic Blood International; name changed to Oxygen Biotherapeutics in 2008

Shift in research from use as RBC substitute to other medical applications. Currently in phase II trials in Switzerland for treatment of traumatic brain injury.

Perftoran

Perftoran

Approved for use in Russia and Mexico.

2682_Ch01_001-025 28/05/12 12:22 PM Page 15

Chapter 1 Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends

Dense granules or bodies are smaller and fewer in number (2 to 10 per platelet) and appear as dense opaque granules in transmission electron microscopy (TEM) preparations.8 Dense granules contain storage ADP, ATP, ionic calcium, serotonin, and phosphates. Platelet ADP and ATP are present in two cellular pools—a metabolic pool and a storage pool. The metabolic pool meets the platelet’s ongoing metabolic needs, and the storage pool, which is located in the dense granules, is released when the platelet is stimulated.19 Lysosomes contain microbicidal enzymes, neutral proteases, and acid hydrolases. Glycogen granules are also found within the organelle zone and function in platelet metabolism. The estimated 10 to 60 mitochondria present per platelet require glycogen as their source of energy for metabolism.8 In the resting platelet, approximately 15% ATP (energy) production is generated by glycolysis and 85% by oxygen consumption through the tricarboxylic acid (TCA) cycle.19 In the activated state, about half the ATP production in platelets occurs through the glycolytic pathway, increasing the rate of lactate production.8 Platelets circulate in an inactivated state and require minimal stimulation for activation, ensuring their immediate availability for hemostasis.

The Platelet Storage Lesion Basic Concepts Platelet storage still presents one of the major challenges to the blood bank because of the limitations of storing platelets. In the United States, which has a storage limit of 5 days, approximately 30% of the platelet inventory is discarded either by the blood supplier or the hospital blood bank.41 The two main reasons for the 5-day shelf-life for platelets is bacterial contamination at incubation of 22°C and the loss of platelet quality during storage (known as the platelet storage lesion). During storage, a varying degree of platelet activation occurs that results in release of some intracellular granules and a decline in ATP and ADP. This platelet activation often results in temporary aggregation of platelets into large sheets that must be allowed to rest for the aggregation to be reversed, especially when the platelet concentrates (PCs) are prepared with the plateletrich-plasma (PRP) method. The reduced oxygen tension (pO2) in the plastic platelet storage container results in the platelets increasing the rate of glycolysis to compensate for the decrease in ATP regeneration from the oxidative (TCA) metabolism. This increases glucose consumption and causes an increase in lactic acid that must be buffered. This results in a fall in pH. During the storage of PCs in plasma, the principal buffer is bicarbonate. When the bicarbonate buffers are depleted during PC storage, the pH rapidly falls to less than 6.2, which is associated with a loss of platelet viability. In addition, when pH falls below 6.2, the platelets swell and there is a disk-to-sphere transformation in morphology that is associated with a loss of membrane integrity. The

15

platelets then become irreversibly swollen, aggregate together, or lyse, and when infused, will not circulate or function. During storage of PCs, the pH will remain stable as long as the production of lactic acid does not exceed the buffering capacity of the plasma or other storage solution.

Advanced Concepts The platelet storage lesion results in a loss of platelet quality and viability. When platelets deteriorate during storage, their membranes lose their ability to maintain normal lipid asymmetry and phosphatidylserine becomes expressed on the outer membrane surface.41 The binding of annexin V, which has a high affinity for anionic phospholipids, can be used to measure this loss of membrane integrity using flow cytometry.41 Flow cytometry is also used to measure the platelet degranulation process during storage by detecting the surface expression of CD62P or CD63.41 Measurement of specific platelet α granules such as β-thromboglobulin and platelet factor 4 can also assess platelet degranulation during storage. Generally, the quality-control measurements required by various accreditation organizations for platelet concentrates include platelet concentrate volume, platelet count, pH of the unit, and residual leukocyte count if claims of leukoreduction are made.42 In addition, immediately before distribution to hospitals, a visual inspection is made that often includes an assessment of platelet swirl.41 The absence of platelet swirling is associated with the loss of membrane integrity during storage, resulting in the loss of discoid shape with irreversible sphering. Box 1–4 lists the in vitro platelet assays that have been correlated with in vivo survival. Clinical Use of Platelets Platelet components are effectively used to treat bleeding associated with thrombocytopenia, a marked decrease in platelet number. The efficacy of the transfused platelet concentrates is usually estimated from the corrected count increment (CCI) of platelets measured after transfusion. It should be noted that the CCI does not evaluate or assess function of the transfused platelets.43 Platelets are also transfused prophylactically to increase the circulating platelet count in hematology-oncology thrombocytopenic patients to prevent bleeding secondary BOX 1–4

In Vitro Platelet Assays Correlated With In Vivo Survival • • • • •

pH Shape change Hypotonic shock response Lactate production pO2

2682_Ch01_001-025 28/05/12 12:22 PM Page 16

16

PART I

Fundamental Concepts

to drug and radiation therapy. Platelets are also utilized in some instances to treat other disorders in which platelets are qualitatively or quantitatively defective because of genetic reasons. In the 1950s and 1960s, platelet transfusions were given as freshly drawn whole blood or platelet-rich plasma. Circulatory overload quickly developed as a major complication of this method of administering platelets. Since the 1970s, platelets have been prepared from whole blood as concentrates in which the volume per unit is near 50 mL in contrast to the 250- to 300-mL volume of platelet-rich plasma units. Today, platelets are prepared as concentrates from whole blood and increasingly by apheresis. The 2007 National Blood Collection and Utilization Survey found that only 17% of platelet doses in the United States were whole blood derived (WBD). Platelets still remain as the primary means of treating thrombocytopenia, even though therapeutic responsiveness varies according to patient conditions and undefined consequences of platelet storage conditions.44,45 (See Chapter 13 for the methods for preparing platelet concentrates.)

Current Conditions for Platelet Preservation (Platelet Storage) Basic Concepts Platelet concentrates prepared from whole blood and apheresis components are routinely stored at 20°C to 24°C, with continuous agitation for up to 5 days. FDA standards define the expiration time as midnight of day 5. Primarily flatbed and circular agitators are in use. There are a number of containers in use for 5-day storage of WBD and apheresis platelets. In the United States, platelets are being stored in a 100% plasma medium, unless a platelet additive solution is used (see section on platelet additives on page 19). Although platelets can be stored at 1°C to 6°C for 48 hours,46 it does not appear that this is a routine practice. History of Platelet Storage: Rationale for Current Conditions Advanced Concepts The conditions utilized to store platelets have evolved since the 1960s as key parameters that influence the retention of platelet properties. Initially, platelets were stored at 1°C to 6°C, based on the successful storage of RBCs at this temperature range. A key study in 1969 by Murphy and Gardner showed that cold storage at 1°C to 6°C resulted in a marked reduction in platelet in vivo viability, manifested as a reduction in in vivo life span, after only 18 hours of storage.47 This study also identified for the first time that 20°C to 24°C (room temperature) should be the preferred range, based on viability results. The reduction in viability at 1°C to 6°C was associated with conversion of the normal discoid shape to a form that

is irreversibly spherical. This structural change is considered to be the factor responsible for the deleterious effects of cold storage. When stored even for several hours at 4°C, platelets do not return to their disk shape upon rewarming. This loss of shape is probably a result of microtubule disassembly. Based on many follow-up studies, platelets are currently stored at room temperature. These studies provided an understanding of the factors that influenced the retention of platelet viability and the parameters that needed to be considered to optimize storage conditions. One factor identified as necessary was the need to agitate platelet components during storage, although initially the rationale for agitation was not understood.48,49 Subsequently, agitation has been shown to facilitate oxygen transfer into the platelet bag and oxygen consumption by the platelets. The positive role for oxygen has been associated with the maintenance of platelet component pH.50 Maintaining pH was determined to be a key parameter for retaining platelet viability in vivo when platelets were stored at 20°C to 24°C. Although storage itself was associated with a small reduction in post-infusion platelet viability, an enhanced loss was observed when the pH was reduced from initial levels of near 7 to the range of 6.8 to 6.5, with a marked loss when the pH was reduced to levels below 6.49 A pH of 6 was initially the standard for maintaining satisfactory viability. The standard was subsequently changed to 6.2 with the availability of additional data. As pH was reduced from 6.8 to 6.2, the platelets progressively changed shape from disks to spheres. This change is irreversible when the pH falls to less than 6.2.19 In the 1970s, when WBD platelets were initially stored as concentrates, a major problem was a marked reduction in pH in many concentrates. This limited the storage period to 3 days. The containers being used for storage were identified as being responsible for the fall in pH because of their limiting gas transfer properties for oxygen and carbon dioxide. Carbon dioxide buildup from aerobic respiration and as the end product of plasma bicarbonate depletion also influenced the fall in pH. The gas transport properties of a container are known to reflect the container material, the gas permeability of the wall of the plastic container, the surface area of the container available for gas exchange, and the thickness of the container. Insufficient agitation may also be a factor responsible for pH reduction because agitation facilitates gas transport into the containers.

Storage in Second-Generation Containers Understanding the factors that led to the reduction in pH in first-generation platelet containers resulted in the development of second-generation containers, starting around 1982. The second-generation containers, with increased gas transport properties (allowing increased oxygen transport and carbon dioxide escape), are available and are being utilized for storing platelets for 5 days without pH substantially falling. Such containers are in use for WBD PCs and apheresis components.

2682_Ch01_001-025 28/05/12 12:22 PM Page 17

Chapter 1 Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends

Containers for platelet storage were originally constructed from polyvinyl chloride (PVC) plastic containing a phthalate plasticizer. The second-generation containers are constructed in some cases with PVC and in other cases with polyolefin plastic. For most PVC containers, alternative plasticizers (trimellitate and citrate based) have been used to increase gas transport. The nominal volumes of the containers are 300 to 400 mL and 1 to 1.5 L for WBD platelet concentrates and apheresis components, respectively. The size of the containers for apheresis components reflects the increased number of platelets that are being stored and hence the need for a larger surface area to provide adequate gas transport properties for maintaining pH levels near the initial level of 7 even after 5 days of storage. Box 1–5 lists factors that should be considered when using 5-day platelet storage containers.

Storing Platelets Without Agitation for Limited Times Although platelet components should be stored with continuous agitation, there are data that suggest that platelet properties, based on in vitro studies, are retained when agitation is discontinued for up to 24 hours during a 5-day storage period.51,52 This is probably related to the retention of satisfactory oxygen levels with the second-generation containers when agitation is discontinued, as occurs by necessity when platelets are shipped over long distances by, for example, overnight courier.

Measurement of Viability and Functional Properties of Stored Platelets Viability indicates the capacity of platelets to circulate after infusion without premature removal or destruction. Platelets have a life span of 8 to 10 days after release from megakaryocytes. Storage causes a reduction in this parameter, even when pH is maintained. Platelet viability of stored platelets is determined by measuring pretransfusion and post-transfusion platelet counts (1 hour and/or 24 hours) and expressing the difference based on the number of platelets transfused (corrected count increment) or by determining the disappearance

BOX 1–5

Factors to Be Considered When Using 5-Day Plastic Storage Bags • Temperature control of 20°C to 24°C is critical during platelet preparation and storage. • Careful handling of plastic bags during expression of platelet-poor plasma helps prevent the platelet button from being distributed and prevents removal of excess platelets with the platelet-poor plasma. • Residual plasma volumes recommended for the storage of platelet concentrates from whole blood (45 to 65 mL). • For apheresis platelets, the surface area of the storage bags needs to allow for the number of platelets that will be stored.

17

rate of infused radiolabeled platelets to normal individuals whose donation provided the platelets. The observation of the swirling phenomenon caused by discoid platelets when placed in front of a light source has been used to obtain a semiqualitative evaluation of the retention of platelet viability properties in stored units.53 The extent of shape change and the hypotonic shock response in in vitro tests appears to provide some indication about the retention of platelet viability properties.54 Function is defined as the ability of viable platelets to respond to vascular damage in promoting hemostasis. Clinical assessment of hemostasis is being increasingly used. The maintenance of pH during storage at 20°C to 24°C has been associated with the retention of post-transfusion platelet viability and has been the key issue that has been addressed to improve conditions for storage at this temperature. There is also the issue of retaining platelet function during storage. Historically, room temperature storage has been thought to be associated with a reduction in platelet functional properties. However, the vast transfusion experience with room temperature platelets worldwide indicates that such platelets have satisfactory function. As has been suggested many times over the last 30 years, it is possible that room temperature–stored platelets undergo a rejuvenation of the processes that provide for satisfactory function upon introduction into the circulation.55,56 The better functionality of cold-stored platelets, based on some studies, especially ones conducted in the 1970s, may have reflected an undesirable activation of platelet processes as a result of storing platelets at a temperature range of 1°C to 6°C. Activation is a prerequisite for platelet function in hemostasis. During storage, it takes different forms. Even with storage at 20°C to 24°C, there is some activation, as judged by the release of granular proteins such as p-selectin (CD62) and platelet factor 4 and granular adenine nucleotides. There are some data that suggest that specific inhibitors of the activation processes may have a beneficial influence during storage.57 Table 1–14 summarizes platelet changes during storage (the platelet storage lesion). It should be noted that except for change in pH, the effect of in vitro changes on post-transfusion platelet survival and function is unknown, and some of the changes may be reversible upon transfusion.58

Platelet Storage and Bacterial Contamination Basic Concepts The major concern associated with storage of platelets at 20°C to 24°C is the potential for bacterial growth, if the prepared platelets contain bacteria because of contamination at the phlebotomy site or if the donor has an unrecognized bacterial infection.59 Environmental contamination during processing and storage is another potential, though less common, source of bacteria. Room temperature storage and the presence of oxygen provide a good environment for bacterial proliferation. Sepsis due to contaminated

2682_Ch01_001-025 28/05/12 12:22 PM Page 18

18

PART I

Fundamental Concepts

Table 1–14 The Platelet Storage Lesion CHARACTERISTIC

CHANGE OBSERVED

Lactate

Increased

pH

Decreased

ATP

Decreased

Morphology scores change from discoid to spherical (loss of swirling effect)

Decreased

Degranulation (β-thromboglobulin, platelet factor 4)

Increased

Platelet activation markers (P-selectin [CD62P] or CD63)

Increased

Platelet aggregation

Drop in responses to some agonists

platelets is the most common infectious complication of transfusion.60 A large-scale study at American Red Cross (ARC) regional blood centers from 2004 to 2006 detected bacteria in 186 out of 1,004,206 donations for a contamination rate of approximately 1 in 5,400.61 Although the occurrence of patient sepsis is much lower, particularly troublesome is the fact that some septic episodes have led to patient deaths. An estimated 10% to 40% of patients transfused with a bacterially contaminated platelet unit develop life-threatening sepsis.60 As a result, in 2002 the College of American Pathologists (CAP) added a requirement for laboratories to have a method to screen platelets for bacterial contamination, and AABB introduced a similar requirement in 2004.

Advanced Concepts There are three commercial systems approved by the FDA for screening platelets for bacterial contamination: BacT/ALERT (bioMérieux), eBDS (Pall Corp.), and Scansystem (Hemosystem). BacT/ALERT and eBDS are culturebased systems. As the level of bacteria in the platelets at the time of collection can be low, samples are not taken until after at least 24 hours of storage. This provides time for any bacteria present to replicate to detectable levels. BacT/ ALERT measures bacteria by detecting a change in carbondioxide levels associated with bacterial growth.62 This system provides continuous monitoring of the platelet sample–containing culture bottles, which are held for the shelf-life of the platelet unit or until a positive reaction is detected. The eBDS system measures the oxygen content of the air within the sample pouch following incubation for 18 to 30 hours. A decrease in oxygen level indicates the presence of bacteria. BacT/ALERT and eBDS are the most widely used systems for screening platelets in the United States, and studies have documented good sensitivity and specificity;

however, false-negative test results have been documented. With both culture systems, the need to delay sampling and the requirement for incubation delay entry of the platelet products into inventory. Box 1–6 lists the disadvantages associated with the use of culture methods for the detection of bacterial contamination of platelets. The third bacterial detection method approved by the FDA, Scansystem, is a laser-based, scanning cytometry method. In the United States, 100% of apheresis platelets are tested by the collection facility using culture-based assays.63 Because screening individual units of WBD platelets by these methods is time-consuming, expensive, and uses a significant amount of the product, less sensitive methods, such as gram staining and dipstick tests for pH and glucose, were initially used for screening. Since these methods have a sensitivity of about only 50%, many transfusion services chose not to transfuse WBD platelets. This practice made it difficult for some blood banks to meet the demand for apheresis platelets, and WBD platelets became underutilized. In November 2009, the FDA approved the first rapid test to detect bacteria in WBD platelets—the Pan Genera Detection (PGD) test (Verax Biomedical). The PDG test, which was previously approved by the FDA for testing leukocyte-reduced platelets as an adjunct to culture, is an immunoassay that detects lipoteichoic acids on grampositive bacteria and lipopolysaccharides on gram-negative bacteria. Both aerobes and anaerobes are detected. The test can be performed on pools of up to 6 units of WBD platelets. A sample of only 500 µl is required. Following pretreatment, the sample is loaded into a disposable plastic cartridge with built-in controls that turn from yellow to blue-violet when the test is ready to be read, in approximately 20 minutes. A pink-colored bar in either the grampositive or gram-negative test window indicates a positive result. The manufacturer states that the system has a specificity of 99.8% and can detect bacteria at 103 to 105 colonyforming units (CFU) per milliliter.64 The PGD test can be performed by transfusion services just prior to release of platelet products. The optimum time for sampling is at least 72 hours after collection. With the availability of this rapid and sensitive method for screening WBD platelets, AABB issued Interim Standard 5.1.5.1.1, which prohibits the use of the less-sensitive methods (microscopy, pH, glucose) after January 31, 2011.65 Transfusion services must either

BOX 1–6

Disadvantages of Culture Methods for Detection of Bacterial Contamination of Platelets • • • • •

Product loss due to sampling Delay in product release, further reducing already short shelf-life False-negative results Cost Logistical problems of culturing WBD platelets

2682_Ch01_001-025 28/05/12 12:22 PM Page 19

Chapter 1 Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends

obtain their platelets from a collection facility that performs an approved test for bacterial contamination, or they must perform an approved test themselves.66 At this time, the approved tests are bacterial culture or the Verax PGD test. The practice of screening platelets for bacterial contamination has reduced, but not eliminated, the transfusion of contaminated platelet products. False-negative cultures can occur when bacteria are present in low numbers and when the pathogen is a slow-growing organism. The American Red Cross received reports of 20 septic transfusion reactions from 2004 to 2006 following transfusion of culturenegative platelets. Eighty percent of the septic reactions were due to Staphylococcus spp., and 65% occurred with products transfused on day 5 after collection. Three of these reactions were fatal, for a fatality rate of 1 per 498,711 distributed products.61 Because current bacterial screening methods are not 100% sensitive, they must be supplemented by other precautions, such as the donor interview and proper donor arm disinfection. Another more recent precaution is the diversion of the first aliquot (about 20 to 30 mL) of collected blood into a separate but connected diversion pouch. This procedure minimizes the placement of skin plugs, the most common source of bacterial contamination, into the platelet products. The 2007 National Blood Collection and Utilization Survey found that 50.4% of blood collection facilities used diversion devices for collecting apheresis platelets, and one study found that diversion reduced bacterial contamination by 40% to 88%.67 In view of the ability to test for bacterial contamination and the use of diversion pouches and sterile docking instruments, there is now interest in being able to store pools of platelets up to the outdate of the individual concentrates. The retention of platelet properties during storage of pools has been shown in a number of studies. Traditionally, four to six WBD platelets are pooled into a single bag by the transfusion service just prior to issue. This facilitates transfusion but reduces the shelf-life of the platelets to 4 hours, because they are prepared in an open system. In 2005, the FDA approved the use of prestorage pooled platelets prepared by Acrodose Systems (Pall Corp.). Acrodose platelets are pooled ABO-matched, leukoreduced WBD platelets that have been cultured and are ready for transfusion. Because they are produced in a closed system, they can be stored for 5 days from collection. They provide a therapeutic dose equivalent to apheresis platelets and at a lower cost,68 but they do expose the recipient to multiple donors. A recent study comparing transfusion reactions from prestorage-pooled platelets, apheresis platelets, and poststorage-pooled WBD platelets found no difference in reaction rates among the different products.69 Prestorage-pooled platelets may prove to be a useful adjunct to apheresis platelets, which are often in short supply, and may lead to improved utilization of WBD platelets.

19

Current Trends in Platelet Preservation Research Advanced Concepts Research and development in platelet preservation is being pursued in many directions, including the following: 1. Development of methods that would allow platelets to be stored for 7 days 2. Development of additive solutions, also termed synthetic media 3. Development of procedures to reduce and inactivate the level of pathogens that may be in platelet units 4. Development of platelet substitutes 5. New approaches for storage of platelets at 1°C to 6°C 6. The development of processes to cryopreserve platelets

Storage for 7 Days at 20°C to 24°C In 1984, the FDA extended platelet storage from 5 to 7 days. Reports of septic transfusion reactions increased following this change, and in 1986 the storage time was changed back to 5 days. With the implementation of bacterial screening of platelets and its impact on their available shelf-life, there is renewed interest in being able to store platelets for 7 days. In 2005, the FDA approved a study called “Post Approval Surveillance Study of Platelet Outcomes, Release Tested” (PASSPORT) to collect data on the safety of apheresis platelets tested with an FDAapproved bacterial detection test and stored for 7 days. The study was suspended in 2008 because of safety concerns when interim data and published studies suggested that culture at 24 hours after collection may miss up to 50% of contaminated apheresis platelet units.70 FDA and industry representatives discussed modifications to the study protocol that might increase the safety of 7-day platelets and allow resumption of the study—for example, increasing the size of the culture inoculum, performing anaerobic cultures in addition to aerobic cultures, and performing a second culture at 5 days of storage. Because consensus could not be reached, the PASSPORT study was not resumed.70 Although work toward approval of safe and efficacious 7-day platelets is likely to continue, the shelf-life for platelets at this time remains 5 days.

Storage with Additive Solutions Platelet additive solutions (PASs) were first developed in the 1980s71 and have been used in Europe since 1995 to replace a large portion of the plasma in platelet suspensions prepared from whole blood by the buffy coat method. In 2010, the FDA approved the first PAS for use in the United States. This additive, called PAS-C, was approved for storage of apheresis platelets collected by the AMICUS Separator System (Fenwal/Baxter) for up to 5 days. Other PASs are under development and may gain FDA approval in the future.72

2682_Ch01_001-025 28/05/12 12:22 PM Page 20

20

PART I

Fundamental Concepts

PASs are designed to support platelets during storage in reduced amounts of residual plasma. Historically, platelets have been stored in 100% plasma. With the addition of a PAS, residual plasma can be reduced to 30% to 40%71 (35% with InterSol). One advantage is that this approach provides more plasma for fractionation. In addition, there are data indicating that optimal additive solutions may improve the quality of platelets during storage, reduce adverse effects associated with transfusion of plasma, and promote earlier detection of bacteria.63,73,74 Box 1–7 lists the advantages of using a platelet additive solution for platelet storage. Research is being conducted to improve the additive solutions in use. Gulliksson suggested that platelets could be stored for at least 18 to 20 days at 20°C to 24°C with an optimized additive medium based on considerations that indicate that storage could well inhibit platelet aging with the appropriate environments/medium.75 Platelet additive solutions in use and those being developed contain varying quantities of citrate, phosphate, potassium, magnesium, and acetate. Citrate, magnesium, and potassium control platelet activation.76 Acetate serves as a substrate for aerobic respiration (mitochondrial metabolism) while also providing a way to maintain pH levels as it reacts with hydrogen ions when it is first utilized. Some formulations also contain glucose, which seems to maintain pH better beyond day 5. This might give glucose-containing PASs an advantage over nonglucose PASs if extended storage of platelets becomes a reality.77 Currently, glucose-containing PASs are not widely used because glucose caramelizes during the steam sterilization process that is used.78 When nonglucose PASs are used, at least 20% to 35% of the plasma must be retained in order to provide the glucose the platelets need during storage.78

Procedures to Reduce and Inactivate Pathogens Despite sensitive methods to detect bacteria in platelets, septic transfusion reactions still occur. As for RBCs, procedures are being developed to treat platelet components to reduce or inactivate any residual pathogens (bacteria, viruses, parasites) that may be present. The term pathogen reduction (PR) is preferred to pathogen inactivation (PI) because inactivation may not be complete.79 PR/PI procedures could

BOX 1–7

Advantages of Using Platelet Additive Solutions • Optimizes platelet storage in vitro • Saves plasma for other purposes (e.g., transfusion or fractionation) • Facilitates ABO-incompatible platelet transfusions • Reduces plasma-associated transfusion side effects, such as febrile and allergic reactions, and may reduce risk of transfusion-related acute lung injury (TRALI) • Improves effectiveness of photochemical pathogen reduction technologies • Potentially improves bacterial detection

potentially add an additional level of safety by protecting against unknown and newly emerging pathogens.79,80 Two PR/PI methods, both using photochemical technologies to target nucleic acids, are approved for use in Europe but are approved only for clinical trials in the United States.81 The targeting of nucleic acids is possible because platelets, like RBCs, do not contain functional nucleic acids. In the INTERCEPT system (Cerus Corp.), amotosalen is activated by ultraviolet (UV) light and binds to the nucleic acid base pairs of pathogens, preventing replication.82 This system was approved for clinical use in Europe in 2002. The Mirasol PRT system (CaridianBCT Biotechnologies) uses riboflavin (vitamin B2) and UV light to cause irreversible changes to the nucleic acids of pathogens.83 Many studies suggest that PR of platelets is safe and effective; however, additional studies involving larger groups and pediatric patients are needed.80 Some argue that since most patients who receive platelets also receive red cells, PR of platelets will be of limited value until there is an equivalent method for red cells.79

Development of Platelet Substitutes In view of the short shelf-life of liquid-stored platelet products, there has been a long-standing interest to develop platelet substitute products that maintain hemostatic function. Platelet substitutes are in the early stages of development. It is understood that platelet substitutes may have use only in specific clinical situations because platelets have a complex biochemistry and physiology. Besides having a long shelf-life, platelet substitutes appear to have reduced potential to transmit pathogens as a result of the processing procedures. A number of different approaches have been utilized.84 Apparently, one approach with the potential for providing clinically useful products is the use of lyophilization. Two products prepared from human platelets are in preclinical testing. One preparation uses washed platelets treated with paraformaldehyde, with subsequent freezing in 5% albumin and lyophilization.85 These platelets on rehydration have been reported to have hemostatic effectiveness in different animal models. A second method involves the freeze-drying of trehalose-loaded platelets.86 Additional products that are apparently being developed include fibrinogen-coated albumin microcapsules and microspheres and modified RBCs with procoagulant properties as a result of fibrinogen binding. Fibrinogen is being used because in vivo this protein cross-links activated platelets to form platelet aggregates as part of the hemostatic process. Two other approaches include the development of plateletderived microparticles that can stop bleeding and liposomebased hemostatic products.84

New Approaches for Storage of Platelets at 1°C to 6°C Although storage of platelets at 1°C to 6°C was discontinued many years ago, there has been an interest in developing ways to overcome the storage lesion that occurs at 1°C to 6°C.87 The rationale for the continuing effort reflects concerns about

2682_Ch01_001-025 28/05/12 12:22 PM Page 21

Chapter 1 Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends

storing and shipping platelets at 20°C to 24°C, especially the chance for bacterial proliferation. Refrigeration would significantly reduce the risk of bacterial contamination, allowing for longer storage. Many approaches have been attempted without success, although early results showed some promise. The approaches primarily involve adding substances to inhibit cold-induced platelet activation, as this is thought to be the key storage lesion. Two reports concluded that platelets stored at 1°C to 6°C could conceivably have satisfactory in vivo viability and function if the surface of the platelets were modified to prevent the enhanced clearance (unsatisfactory viability) from circulation.88,89 Based on animal studies, it was suggested that coldinduced spherical platelets can remain in the circulation if abnormal clearance is prevented. Spherical platelets, manifested as a result of cold storage, have been assumed to be a trigger for low viability. The specific approach involves the

21

enzymatic galactosylation of cold-stored platelets to modify specifically one type of membrane protein. The addition of uridine diphosphate galactose is the vehicle for the modificaiton.89

Frozen Platelets Although considered a research technique and not licensed by the FDA, frozen platelets are used occasionally in the United States as autologous transfusions for patients who are refractory to allogeneic platelets. Platelets are collected by apheresis, the cryopreservative dimethyl sulfoxide (DMSO) is added, and the platelets are frozen at –80°C. The frozen platelets can be stored for up to 2 years. Prior to transfusion, the platelets are thawed and centrifuged to remove the DMSO. Although in vivo recovery after transfusion is only about 33%, the platelets seem to function effectively.5

SUMMARY CHART

     

 

Each unit of whole blood collected contains approximately 450 mL of blood and 63 mL of anticoagulantpreservative solution or approximately 500 mL of blood and 70 mL of anticoagulant-preservative solution. A donor can give blood every 8 weeks. As of 2011, samples from donors of each unit of donated blood are tested by 10 screening tests for infectious diseases markers. Glycolysis generates approximately 90% of the ATP needed by RBCs, and 10% is provided by the pentose phosphate pathway. Seventy-five percent post-transfusion survival of RBCs is necessary for a successful transfusion. ACD, CPD, and CP2D are approved preservative solutions for storage of RBCs at 1°C to 6°C for 21 days, and CPDA-1 is approved for 35 days. Additive solutions (Adsol, Nutricel, Optisol) are approved in the United States for RBC storage for 42 days. Additive-solution RBCs have been shown to be appropriate for neonates and pediatric patients. RBCs have been traditionally glycerolized and frozen within 6 days of whole blood collection in CPD or CPDA-1 and can be stored for 10 years from the date of freezing. Rejuvesol is the only FDA-approved rejuvenation solution used in some blood centers to regenerate ATP and 2,3-DPG levels before RBC freezing. Rejuvenation is used primarily to salvage O-type and rare RBC units that are at outdate or with specific anticoagulant-preservative solution up to 3 days past outdate.

   

Research is being conducted to improve on the current additive solutions. Research is being conducted to develop procedures to reduce or inactivate pathogens. RBC substitutes under investigation include hemoglobin-based oxygen carriers and perfluorocarbons. A platelet concentrate should contain a minimum of 5.5 ⫻ 1010 platelets (in 90% of the sampled units according to AABB standards) in a volume routinely between 45 and 65 mL that is sufficient to maintain a pH of 6.2 or greater at the conclusion of the 5-day storage period. When platelet concentrates (usually 4 to 6) are pooled using an open system, the storage time changes to 4 hours. A new method of pooling that uses a closed system allows the pool to be stored for 5 days from the date of collection. Apheresis components contain 4 to 6 times as many platelets as a PC prepared from whole blood. They should contain a minimum of 3.0 ⫻ 1011 platelets (in 90% of the sampled units). Platelet components are stored for up to 5 days at 20°C to 24°C with continuous agitation. When necessary, as during shipping, platelets can be stored without continuous agitation for up to 24 hours (at 20°C to 24°C) during a 5-day storage period. Platelets are rarely stored at 1°C to 6°C. If a platelet bag is broken or opened, the platelets must be transfused within 4 hours when stored at 20°C to 24°C.

2682_Ch01_001-025 28/05/12 12:22 PM Page 22

22

PART I

Fundamental Concepts

Review Questions 1. What is the maximum volume of blood that can be col-

lected from a 110-lb donor, including samples for processing? a. 450 mL b. 500 mL c. 525 mL d. 550 mL 2. How often can a blood donor donate whole blood? a. b. c. d.

Every 24 hours Once a month Every 8 weeks Twice a year

3. When RBCs are stored, there is a “shift to the left.” This

means: a. Hemoglobin oxygen affinity increases, owing to an increase in 2,3-DPG. b. Hemoglobin oxygen affinity increases, owing to a decrease in 2,3-DPG. c. Hemoglobin oxygen affinity decreases, owing to a decrease in 2,3-DPG. d. Hemoglobin oxygen affinity decreases, owing to an increase in 2,3-DPG. 4. The majority of platelets transfused in the United States

today are: a. Whole blood–derived platelets prepared by the platelet-rich plasma method. b. Whole blood–derived platelets prepared by the buffy coat method. c. Apheresis platelets. d. Prestorage pooled platelets. 5. Which of the following anticoagulant preservatives pro-

vides a storage time of 35 days at 1°C to 6°C for units of whole blood and prepared RBCs if an additive solution is not added? a. ACD-A b. CP2D c. CPD d. CPDA-1 6. What are the current storage time and storage tempera-

ture for platelet concentrates and apheresis platelet components? a. 5 days at 1°C to 6°C b. 5 days at 24°C to 27°C c. 5 days at 20°C to 24°C d. 7 days at 22°C to 24°C

7. What is the minimum number of platelets required in a

platelet concentrate prepared from whole blood by centrifugation (90% of sampled units)? a. 5.5 ⫻ 1011 b. 3 ⫻ 1010 c. 3 ⫻ 1011 d. 5.5 ⫻ 1010 8. RBCs can be frozen for: a. b. c. d.

12 months. 1 year. 5 years. 10 years.

9. What is the minimum number of platelets required in

an apheresis component (90% of the sampled units)? a. 3 ⫻ 1011 b. 4 ⫻ 1011 c. 2 ⫻ 1011 d. 3.5 ⫻ 1011 10. Whole blood and RBC units are stored at what

temperature? a. 1°C to 6°C b. 20°C to 24°C c. 37°C d. 24°C to 27°C 11. Additive solutions are approved for storage of red blood

cells for how many days? a. 21 b. 42 c. 35 d. 7 12. One criterion used by the FDA for approval of new preser-

vation solutions and storage containers is an average 24-hour post-transfusion RBC survival of more than: a. 50%. b. 60%. c. 65%. d. 75%. 13. What is the lowest allowable pH for a platelet compo-

nent at outdate? a. 6 b. 5.9 c. 6.8 d. 6.2 14. Frozen and thawed RBCs processed in an open system

can be stored for how many days/hours? a. 3 days b. 6 hours c. 24 hours d. 15 days

2682_Ch01_001-025 28/05/12 12:22 PM Page 23

Chapter 1 Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends

15. What is the hemoglobin source for hemoglobin-based

oxygen carriers in advanced clinical testing? a. Only bovine hemoglobin b. Only human hemoglobin c. Both bovine and human hemoglobins d. None of the above 16. Which of the following occurs during storage of red

blood cells? a. pH decreases b. 2,3-DPG increases c. ATP increases d. plasma K+ decreases 17. Nucleic acid amplification testing is used to test donor

blood for which of the following infectious diseases? a. Hepatitis C virus b. Human immunodeficiency virus c. West Nile virus d. All of the above 18. Which of the following is NOT an FDA-approved test

for quality control of platelets? a. BacT/ALERT b. eBDS c. Gram stain d. Pan Genera Detection (PGD) test 19. Prestorage pooled platelets can be stored for: a. b. c. d.

4 hours. 24 hours. 5 days. 7 days.

20. Which of the following is the most common cause of

bacterial contamination of platelet products? a. Entry of skin plugs into the collection bag b. Environmental contamination during processing c. Bacteremia in the donor d. Incorrect storage temperature

References 1. Parks, D: Charles Richard Drew, MD 1904–1950. J Natl Med Assoc 71:893–895, 1979. 2. Kendrick, DB: Blood Program in World War II, Historical Note. Washington Office of Surgeon General, Department of Army, Washington, DC, 1964, pp 1–23. 3. United States Department of Health and Human Services: 2009 National Blood Collection and Utilization Survey Report. Retrieved August 2011 from http://www.hhs.gov/ash/bloodsafety/ 2009nbcus.pdf. 4. New York Blood Center. Blood Statistics. Retrieved August 30, 2011 from www.nybloodcenter.org/blood-statistics.do?sid0= 85&page_id=202#bone. 5. Roback, J, Combs, M, Grossman, B, and Hillyer, C: Technical Manual, 16th ed. American Association of Blood Banks, Bethesda, MD, 2009. 6. Stramer, S: Current risks of transfusion-transmitted agents—a review. Arch Pathol Lab Med 131:702–707, 2007. 7. Zou, S, et al: Current incidence and residual risk of hepatitis B infection among blood donors in the United States. Transfusion 49:1609–1620, 2009.

23

8. Harmening, DM: Clinical Hematology and Fundamentals of Hemostasis, 5th ed. FA Davis, Philadelphia, 2009. 9. Mohandas, N, and Chasis, JA: Red blood cell deformability, membrane material properties and shape: Regulation of transmission, skeletal and cytosolic proteins and lipids. Semin Hematol 30:171–192, 1993. 10. Mohandas, N, and Evans, E: Mechanical properties of the genetic defects. Ann Rev Biophys Biomol Struct 23:787–818, 1994. 11. Koch, CG, Li, L, Sessler, DI, et al: Duration of red cell storage and complications after cardiac surgery. N Engl J Med 358(12):1229–1239, 2008. 12. Dumont, LJ, and AuBuchon, JP: Evaluation of proposed FDA criteria for the evaluation of radiolabeled red cell recovery trials. Transfusion 48(6):1053–1060, 2008. 13. Hod, EA, Zhang, N, Sokol, SA, et al: Transfusion of red blood cells after prolonged storage produces harmful effects that are mediated by iron and inflammation. Blood 115(21):4284– 4292, 2010. 14. Luten, M, et al: Survival of red blood cells after transfusion: A comparison between red cells concentrates of different storage periods. Transfusion 48(7):1478–1485, 2008. 15. Zeiler, T, Muller, JT, and Kretschmer, V: Flow-cytometric determination of survival time and 24-hour recovery of transfused red blood cells. Transfus Med Hemother 30:14–19, 2003. 16. Valeri, CR: Preservation of frozen red blood cells. In Simon, TL, Dzik, WH, Snyder, EL, Stowell, CP, and Strauss, RG (eds): Rossi’s Principles of Transfusion Medicine, 3rd ed. Williams & Wilkins, Baltimore, 2002. 17. Ozment, CP, and Turi, JL: Iron overload following red blood cell transfusion and its impact on disease severity. Biochim Biophys Acta 1790(7):694–701, 2009. 18. Beutler, E: Red cell metabolism and storage. In Anderson, KC, and Ness, PM (eds): Scientific Basis of Transfusion Medicine. WB Saunders, Philadelphia, 1994. 19. Simon, TL, Snyder, EL, Stowell, CP, et al (eds): Rossi’s Principles of Transfusion Medicine, 4th ed. Wiley-Blackwell, Malden, MA, 2009. 20. Weinberg, JA, McGwin, G Jr, Marques, MB, et al: Transfusions in the less severely injured: Does age of transfused blood affect outcomes? J Trauma 65(4):794–798, 2008. 21. Offner, PJ, Moore, EE, Biffl, WL, Johnson, JL, and Silliman, CC: Increased rate of infection associated with transfusion of old blood after severe injury. Arch Surg 137(6):711–716, 2002. 22. Vandromme, MJ, et al: Transfusion and pneumonia in the trauma intensive care unit: An examination of the temporal relationship. J Trauma 67(1):97–101, 2009. 23. Högman, CF: Additive system approach in blood transfusion birth of the SAG and Sagman systems. Vox Sang 51:1986. 24. Högman, CF: Recent advances in the preparation and storage of red cells. Vox Sang 67:243–246, 1994. 25. Yasutake, M, and Takahashi, TA: Current advances of blood preservation—development and clinical application of additive solutions for preservation of red blood cells and platelets. Nippon Rinsho 55:2429–2433, 1997. 26. Jain, R, and Jarosz, C: Safety and efficacy as AS-1 red blood cell use in neonates. Transfus Apheresis Sci 24:111–115, 2001. 27. U.S. Department of Health and Human Services, Food and Drug Administration. Code of Federal Regulations, Title 21— Food and Drugs, Blood Products 600–680. U.S. Government Printing Office, Washington, DC, 2010. 28. Valeri, CR, et al: A multicenter study of in-vitro and in-vivo values in human RBCs frozen with 40% (wt/vol) glycerol and stored after deglycerolization for 15 days at 4°C in AS-3: assessment of RBC processing in the ACP 215. Transfusion 41:933–939, 2001. 29. Klein, HG, Glynn, SA, Ness, PM, and Blajchman, MA: Research opportunities for pathogen reduction/inactivation of blood components: Summary of an NHLBI workshop. Transfusion 49:1262–1268, 2009.

2682_Ch01_001-025 28/05/12 12:22 PM Page 24

24

PART I

Fundamental Concepts

30. Kruskall, MS, et al: Transfusion to blood group A and O patients of group B RBCs that have been enzymatically converted to group O. Transfusion 40:1290–1298, 2000. 31. Arteriocyte: Cellular Therapies Medical Systems. Blood Pharming. www.arteriocyte.com. Retrieved August 30, 2011. 32. Giarratana, MC, et al: Proof of principle for transfusion of in vitro generated red blood cells. Published online before print. DOI:10.1182/blood-2011-06-362038; Blood September 1, 2011. 33. Chen, J, Scerbo, M, and Kramer, G: A review of blood substitutes: Examining the history, clinical trial results, and ethics of hemoglobin-based oxygen carriers. Clinics (Sao Paulo) 64(8):803–813, 2009. 34. Reid, TJ: Hb-based oxygen carriers: Are we there yet? Transfusion 43:280–287, 2003. 35. Spahn, DR: Artificial oxygen carriers. Status 2002. Vox Sang 83:(Suppl 1):281–285, 2002. 36. Henkel-Hanke, T, and Oleck, M: Artificial oxygen carriers: a current review. AANA J 75(3):205–211, 2007. 37. Cohn, CS, and Cushing, MM: Oxygen therapeutics: Perfluorocarbons and blood substitute safety. Crit Care Clin 25:399–414, 2009. 38. Natanson, C, Kern, SJ, Lurie, P, Banks, SM, and Wolfe, SM: Cell-free hemoglobin-based blood substitutes and risk of myocardial infarction and death. JAMA 99(19):2304–2312, 2008. 39. Tappenden, J: Artificial blood substitutes. J R Army Med Corps 153(1):3–9, 2007. 40. Oxygen Biotherapeutics. www.oxybiomed.com. Retrieved August 31, 2011. 41. Devine, DV, and Serrano, K: The platelet storage lesion. Clin Lab Med 30: 475–487, 2010. 42. Keitel, S: Guide to the Preparation, Use, and Quality Assurance of Blood Components, 16th ed. Strasbourg (France), Council of Europe Publishing, 2011. 43. Horvath, M, Eichelberger, B, Koren, D, et al: Function of platelets in apheresis platelet concentrates and in patient blood after transfusion as assessed by Impact-R. Transfusion 50: 1036–1042, 2010. 44. Kelly, DL, et al: High-yield platelet concentrates attainable by continuous quality improvement reduce platelet transfusion cost and donor expense. Transfusion 37:482–486, 1997. 45. Van der Meer, PF, Pietersz, R, and Reesink, H: Leukoreduced platelet concentrates in additive solution: An evaluation of filters and storage containers. Vox Sang 81:102–107, 2001. 46. U.S. Department of Health and Human Services, Food and Drug Administration. Code of Federal Regulations, Title 21, Part 640.20 Subpart C–Platelets. U.S. Government Printing Office, Washington, DC, 2010. 47. Murphy, S, and Gardner, FH: Platelet preservation: Effect of storage temperature on maintenance of platelet viability—deleterious effect of refrigerated storage. N Engl J Med 280:1094– 1098, 1969. 48. Slichter, SJ, and Harker, LA: Preparation and storage of platelet concentrates II: Storage variables influencing platelet viability and function. Br J Haematol 34:403–412, 1976. 49. Murphy, S: Platelet storage for transfusion. Semin Hematol 22:165–177, 1985. 50. Murphy, S, and Gardner, FH: Platelet storage at 22°C: Role of gas transport across plastic containers in maintenance of viability. Blood 46:209–218, 1975. 51. Moroff, G, and George, VM: The maintenance of platelet properties upon limited discontinuation of agitation during storage. Transfusion 30:427–430, 1990. 52. Hunter, S, Nixon, J, and Murphy, S: The effect of interruption of agitation on platelet quality during storage for transfusion. Transfusion 41:809–814, 2001. 53. Bertolini, F, and Murphy, S: A multicenter inspection of the swirling phenomenon in platelet concentrates prepared in routine practice. Transfusion 36:128–132, 1996. 54. Holme, S, Moroff, G, and Murphy, S: A multi-laboratory evaluation of in vitro platelet assays: The tests for extent of shape

55. 56. 57. 58. 59. 60. 61.

62. 63. 64. 65.

66. 67. 68. 69. 70.

71.

72. 73.

74. 75. 76.

change and response to hypotonic shock. Transfusion 38:31– 40, 1998. Filip, DJ, and Aster, RH: Relative hemostatic effectiveness of human platelets stored at 4°C and 22°C. J Lab Clin Med 91:618–624, 1978. Owens, M, et al: Post-transfusion recovery of function of 5-day stored platelet concentrates. Br J Haematol 80:539–544, 1992. Holme, S, et al: Improved maintenance of platelet in vivo viability during storage when using a synthetic medium with inhibitors. J Lab Clin Med 119:144–150, 1992. Kaufman, RM: Platelets: Testing, dosing and the storage lesion—recent advances. Hematology Am Soc Hematol Educ Program 492–496, 2006. Brecher, ME, and Hay, SN: The role of bacterial testing of cellular blood products in light of new pathogen inactivation technologies. Blood Therapies Med 3:49–55, 2003. Palavecino, EL, Yomtovian, RA, and Jacobs, MR: Detecting bacterial contamination in platelet products. Clin Lab 52:443–456, 2006. Eder, AF, et al: Bacterial screening of apheresis platelets and the residual risk of septic transfusion reactions: The American Red Cross experience (2004–2006). Transfusion 47(7): 1134–1142, 2007. Macauley, A, et al: Operational feasibility of routine bacterial monitoring of platelets. Transfusion Med 13:189–195, 2003. Dumont, LJ, Wood, TA, Housman, M, et al: Bacterial growth kinetics in ACD-A apheresis platelets: Comparison of plasma and PAS III storage. Transfusion, 51(5): 1079-85, 2011. FDA Clears the First Rapid Test to Detect Bacteria in Pooled Platelets. www.veraxbiomedical.com. Retrieved August 31, 2011. AABB, Association Bulletin #10-05: Suggested options for transfusion services and blood collectors to facilitate implementation of BB/TS Interim Standard 5.1.5.1.1, August 19, 2010. Rapp, H: Interim standard 5.1.5.1.1: What it means for facilities. AABB News, January 2011. McDonald, CP: Bacterial risk reduction by improved donor arm disinfection, diversion and bacterial screening. Transfusion Medicine 16(6):381–396, 2006. AcrodoseSM Platelet: Whole Blood Derived Platelets, Pooled. www.pall.com/medical_43849.asp. Retrieved August 31, 2011. Tormey, CA, et al: Analysis of transfusion reactions associated with prestorage-pooled platelets. Transfusion 49(6):1242– 1247, 2009. Gambro BCT and Fenwal Suspend Passport Post-Market Surveillance Study for 7-Day Platelets. www.fenwalinc.com/En/ Pages/GambroBCTandFenwalSuspendPassportPost-Market SurveillanceStudyfor7-DayPlatelets.aspx Retrieved January 30, 2011. Wagner, SJ, et al: Calcium is a key constituent for maintaining the in vitro properties of platelets suspended in the bicarbonatecontaining additive solution M-sol with low plasma levels. Transfusion 50:1028–1035, 2010. AABB, Association Bulletin #10-06: Information concerning platelet additive solutions, October 4, 2010. Yomtovian, R, and Jacobs, MR: A prospective bonus of platelet storage additive solutions: A reduction in biofilm formation and improved bacterial detection during platelet storage. Transfusion 50(11):2295–2300, 2010. Greco, CA, et al: Effect of platelet additive solution on bacterial dynamics and their influence on platelet quality in stored platelet concentrates. Transfusion 50(11):2344–2352, 2010. Gulliksson, H: Defining the optimal storage conditions for the long-term storage of platelets. Transfusion Med Rev 17:209– 215, 2003. Andreu, G, Vasse, J, Herve, F, Tardivel, R, and Semana, G: Introduction of platelet additive solutions in transfusion practice: Advantages, disadvantages, and benefit for patients. Transfus Clin Biol 14(1):100–106, 2007.

2682_Ch01_001-025 28/05/12 12:22 PM Page 25

Chapter 1 Red Blood Cell and Platelet Preservation: Historical Perspectives and Current Trends 77. Sweeney, J: Additive solutions for platelets: Is it time for North American to go with the flow? Transfusion 49(2):199–201, 2009. 78. Vassallo, RR, et al: In vitro and in vivo evaluation of apheresis platelets stored for 5 days in 65% platelet additive solution/35% plasma. Transfusion 50(11):2376–2385, 2010. 79. Hervig, T, Seghatchian, J, and Apelseth, TO: Current debate on pathogen inactivation of platelet concentrates—to use or not to use? Transfus Apheresis Sci 43:411–414, 2010. 80. McClaskey, J, Xu, M, Snyder, EL, and Tormey, CA: Clinical trials for pathogen reduction in transfusion medicine: A review. Transfus Apheresis Sci 41:217–225, 2009. 81. Klein, HG, Glynn, SA, Ness, PM, and Blajchman, MA: Research opportunities for pathogen reduction/inactivation of blood components: Summary of an NHLBI workshop. Transfusion 49(6):1262–1268, 2009. 82. How INTERCEPT Works. Cerus Corporation, Concord, CA. www.cerus.com/index.cfm/ProductOverview. Retrieved August 31, 2011.

25

83. Mirasol Pathogen Reduction Technology. Caridian BCT Biotechnologies. www.caridianbct.com/location/north-america/ Documents/306690227A-web.pdf. Retrieved August 31, 2011. 84. Blajchman, MA: Substitutes and alternatives to platelet transfusions in thrombocytopenic patients. J Thromb Haemostasis 1:1637–1641, 2003. 85. Fischer, TH, et al: Intracellular function in rehydrated lyophilized platelets. Brit J Haematol 111:167–174, 2000. 86. Crowe, JH, et al: Stabilization of membranes in human platelets freeze-dried with trehalose. Chem Phys Lipids 122:41–52, 2003. 87. Vostal, JG, and Mondoro, TH: Liquid cold storage of platelets: A revitalized possible alternative for limiting bacterial contamination of platelet products. Transfus Med Rev 11:286–295, 1997. 88. Hoffmeister, KM, et al: The clearance mechanism of chilled blood platelets. Cell 112:87–97, 2003. 89. Hoffmeister, KM, et al: Glycosylation restores survival of chilled blood platelets. Science 301:1531–1534, 2003.

2682_Ch02_026-044 22/05/12 11:38 AM Page 26

Chapter

2

Basic Genetics Lorraine Caruccio, PhD, MT(ASCP)SBB

Introduction Classic Genetics Population Genetics Early Genetics and Mendel’s Laws of Inheritance Hardy-Weinberg Principle Inheritance Patterns Cellular Genetics Terminology Mitosis

Meiosis Cell Division Molecular Genetics Deoxyribonucleic Acid Ribonucleic Acid Common Steps in Modern Genetics Techniques

Summary Chart Review Questions References Bibliography

OBJECTIVES 1. Explain Mendel’s laws of independent segregation and random assortment, and describe how he developed them. 2. Correlate the concepts of dominant and recessive traits with examples of the inheritance of blood group antigens. 3. Explain the Hardy-Weinberg principle and how it applies to genetic traits. 4. Given the necessary information, solve Hardy-Weinberg problems for any blood group antigen. 5. Determine the inheritance pattern of a given trait by examining the pedigree analysis. 6. Describe the processes of mitosis and meiosis, and outline the differences between them. 7. Distinguish between X-linked and autosomal traits, and describe how each is inherited. 8. Describe in detail the processes of replication, transcription, and translation, including the basic mechanism of each. 9. List the various types of genetic mutations and describe how they can change the function of living cells and organisms. 10. Describe the cell’s different mechanisms for correcting mutations. 11. Identify some of the ways in which genetics can be used in the modern transfusion laboratory, including the necessary background information for describing modern genetic testing techniques. 12. Describe in general the modern techniques used in the study of genetics.

Introduction One of the most important areas of modern biology is the science of genetics. This chapter covers the basic concepts of genetics necessary to understand its role in modern blood banking. Knowledge of modern methods of analysis is also required to appreciate how problems in genetics are solved and explained. The more blood bank technologists become familiar with these techniques, the faster they can be applied to general use in blood bank laboratories and the faster they

26

can be used to address questions and solve problems in transfusion medicine. A solid understanding of classic genetics, including Mendel’s laws of inheritance and Hardy-Weinberg formulas; cellular concepts that control chromosomes; cellular division such as mitosis and meiosis; and the biochemistry of the molecular structures of the nucleic acids and the proteins that are complexed with them is required to fully understand modern genetics. How these theories, concepts, and principles apply to transfusion medicine should be

2682_Ch02_026-044 22/05/12 11:38 AM Page 27

Chapter 2 Basic Genetics

clearly understood, as genetics is a very dynamic science that has its greatest potential in direct applications. Many areas of transfusion medicine rely on an understanding of blood group genetics and on accurate and sensitive methods of pathogen testing to keep the blood supply safe. Most of the antigens in the various blood group systems (i.e., ABO, Rh, Kell, Kidd, etc.) generally follow straightforward inheritance patterns, usually of a codominant nature. Historically, the major focus and role of genetics in blood banking has been more so in population genetics and inheritance patterns, but now cellular and molecular genetics are equally important. Increasingly, modern genetic techniques are playing a role in analyzing the profile of blood donors and recipients, which was once done only with serologic testing. Transfusion medicine physicians and technologists should still know classical genetics, such as interpretation of familial inheritance patterns. In addition, they must now master modern molecular methods that require a high level of training and skill, such as in restriction mapping, sequencing, polymerase chain reaction (PCR), and gene array technology. (See Chapter 4, “Concepts in Molecular Biology.”) In this chapter, a general overview of genetics at three different levels (population, concerning genetic traits in large numbers of individuals; cellular, which pertains to the cellular organization of genetic material; and molecular, based on the biochemistry of genes and the structures that support them) is provided in some detail. It also gives a brief overview of modern molecular techniques. Chapter 4 explains in greater detail the modern testing methods of molecular biology, including recombinant DNA technology, Southern and Northern blotting, restriction fragment length polymorphism analysis, PCR techniques, and cloning and sequencing.

Classic Genetics The science of genetics is one of the most important areas of modern biology. The understanding of the inheritance of blood group antigens and the testing for disease markers at the molecular level, both of which are vitally important in transfusion medicine, are based on the science of genetics. Modern genetics is based upon the understanding of the biochemical and biophysical nature of nucleic acids, including deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and the various proteins that are part of the chromosomal architecture. In addition, genetics is concerned with population studies and epidemiology. The understanding of inheritance patterns in which genetic traits are followed and analyzed, as well as the biochemical reactions that result in gene mutations that can give rise to new alleles, are highly important in the study of genetics. New alleles can result in new blood groups and disease conditions that affect the health of blood donors and blood recipients. All areas of transfusion medicine are influenced by genetics, including HLA typing, cell processing, parentage studies, viral testing, and blood services, and these would not be

27

completely successful without a clear understanding of the principles of genetics and the laws of inheritance. The antigens present on all blood cells are expressed as a phenotype, but it is the genotype of the organism that controls what antigens may be expressed on the cell. For example, genotyping the donor or recipient DNA using leukocytes can determine which antigens may be present on the cells and therefore which antibodies can be made against them. This is especially true when a clear picture of the red cell antigens present on the red cells of a donor or recipient is not possible or if an antibody screening test gives ambiguous results. Using this simple example, we see that in modern blood banking, genetics has an important role.

Population Genetics The major areas of population genetics of concern to blood banking include Mendel’s laws of inheritance, the HardyWeinberg principle, and inheritance patterns.

Early Genetics and Mendel’s Laws of Inheritance The Swedish biologist Carolus Linnaeus started the first classification system of living things in the 17th century and used the unit of “species” as its principal definition. Determining factors that affected which classification group a species would be put into was based on physical traits and observations. There was no attempt made to understand the underlying reasons for one trait versus another trait occurring in one species or another. The amazing diversity of species and the processes that might contribute to it were not investigated further. In 1859, Charles Darwin published his epic book On the Origin of Species after many years of intense study of various and diverse life-forms. Darwin’s ambition was to understand the diversity of life and how one organism could gain an advantage over another and better survive in a given environment, which is referred to as “natural selection.” It created a revolution in the thinking of modern biology and is still controversial today. The science of genetics found its modern development in the work of Gregor Mendel. Mendel was an Austrian monk and mathematician who used sweet pea plants growing in a monastery garden to study physical traits in organisms and how they are inherited. He determined the physical traits to be due to factors he called elementen within the cell. In modern genetics, we know the physical basis of these so-called elementen are genes within the nucleus of the cell. Mendel chose a good model organism for his observations. He studied the inheritance of several readily observable pea plant characteristics—notably flower color, seed color, and seed shape—and based his first law of inheritance, the law of independent or random segregation, on these results. The first generation in the study, called the parental, pure, or P1 generation, consisted of all red or all white flowers that bred true for many generations. The plants were either homozygous for red flowers (RR, a dominant trait; dominant traits are usually written with uppercase letters)

2682_Ch02_026-044 22/05/12 11:38 AM Page 28

28

PART I

Fundamental Concepts

or homozygous for white flowers (rr, a recessive trait; recessive traits are usually written with lowercase letters). When these plants were crossbred, the second generation, called first-filial, or F1, had flowers that were all red. Thus the dominant trait was the only trait observed. When plants from the F1 generation were crossbred to each other, the second-filial, or F2, generation, of plants had flowers that were red and white in the ratio of 3:1 (Fig. 2–1). All the plants from the F1 generation are heterozygous (or hybrid) for flower color (Rr). The F2 generation has a ratio of three red-flowered plants to one white-flowered plant. This is because the plants that have the R gene, either RR homozygous or Rr heterozygous, will have red flowers because the red gene is dominant. Only when the red gene is absent and the white gene occurs in duplicate, as in the rr homozygous white-flowered plant, will the recessive white gene expression be visible as a phenotype. This illustrates Mendel’s first law, the law of independent segregation. Therefore, each gene is passed on to the next generation on its own. Specifically, Mendel’s first law shows that alleles of genes have no permanent effect on one another when present in the same plant but segregate unchanged by passing into different gametes. An intermediate situation can also occur when alleles exhibit partial dominance. This is observed when the phenotype of a heterozygous organism is a mixture of both homozygous phenotypes seen in the P1 generation. An example of this is plants with red and white flowers that have offspring with pink flowers or flowers that have red and white sections. It is important to remember that although the phenotype does not show dominance or recessive traits, the F1 generation has the heterozygous genotype of Rr. It is essential to understand how a genotype can influence a

Parental

RR

rr

Gametes

R

r

First-Filial

phenotype, and using flower color is a good basic model system to study this. Unlike the flower color of many types of plants, most blood group genes are inherited in a codominant manner. In codominance, both alleles are expressed, and their gene products are seen at the phenotypic level. In this case, one gene is not dominant over its allele, and the protein products of both genes are seen at the phenotypic level. An example of this is seen in Figure 2–2 concerning the MNSs blood group system, in which a heterozygous MN individual would type as both M and N antigen positive. (See Chapter 8, “Blood Group Terminology and the Other Blood Groups.”) Mendel’s second law is the law of independent assortment and states genes for different traits are inherited separately from each other. This allows for all possible combinations of genes to occur in the offspring. Specifically, if a homozygote that is dominant for two different characteristics is crossed with a homozygote that is recessive for both characteristics, the F1 generation consists of plants whose phenotype is the same as that of the dominant parent. However, when the F1 generation is crossed in the F2 generation, two general classes of offspring are found. One is the parental type; the other is a new phenotype called a reciprocal type and represents plants with the dominant feature of one plant and the recessive feature of another plant. Recombinant types occur in both possible combinations. Mendel formulated this law by doing studies with different types of seeds produced by peas and noted that they can be colored green or yellow and textured smooth or wrinkled in any combination. An illustration of independent assortment of Mendel’s second law is given in Figure 2–3; his system of pea plant seed types are used as the example. Mendel’s laws apply to all sexually reproducing diploid organisms whether they are microorganisms, insects, plants, or animals, or people. However, there are exceptions to the Mendelian laws of inheritance. If the genes for separate traits are closely linked on a chromosome, they can be inherited as a single unit. The expected ratios of progeny in F1 matings may not be seen if the various traits being studied are linked.

MN

NN

MN

NN

NN

MM

Rr MN R

r

R

RR

Rr

r

Rr

rr

Second-Filial

MN

MN

MM

MN

MN

NM

NN

MN

NN

MN

NN

Where R = red and r = White Figure 2–1. A schematic illustration of Mendel’s law of separation using flower color.

Figure 2–2. Independent segregation of the codominant genes of M and N.

2682_Ch02_026-044 22/05/12 11:38 AM Page 29

Chapter 2 Basic Genetics Parental

RRYY

Gametes

rryy

Ry

RY

Second-Filial

p

q

p

p2

pq

q

pq

ry

RY

First-Filial

29

RY

rY

Ry

p2 + 2pq + q2 = 1.0

ry

rY

q2

ry Figure 2–4. Common inheritance patterns.

RY

RRYY

RRYy

RrYY

RrYy

Ry

RRYy

RRyy

RrYy

Rryy

rY

RrYY

RrYy

rrYY

rrYy

ry

RrYy

Rryy

rrYy

rryy

Where R = round Y = yellow

r = wrinkled y = green

Figure 2–3. A schematic illustration of Mendel’s law of independent assortment using seed types.

There can also be differences in the gene ratios of progeny of F1 matings, if recombination has occurred during the process of meiosis. An example of this in blood banking is the MNSs system, in which the MN alleles and the Ss alleles are physically close on the same chromosome and are therefore linked. Recombination happens when DNA strands are broken and there is exchange of chromosomal material followed by activation of DNA repair mechanisms. The exchange of chromosomal material results in new hybrid genotypes that may or may not be visible at the phenotypic level. Mendel’s laws of inheritance give us an appreciation of how diverse an organism can be through the variations in its genetic material. The more complex the genetic material of an organism, including the number of chromosomes and the number of genes on the chromosomes, the greater the potential uniqueness of any one organism from another organism of the same species. Also, the more complex the genetic material, the more complex and varied its responses to conditions in the environment. Therefore, as long as control is maintained during cell division and differentiation, organisms with greater genetic diversity and number can have an advantage over other organisms in a given setting.

many mathematical formulations, however, certain ideal situations and various conditions must be met to use the equations appropriately. These criteria are outlined in Box 2–1. In any normal human population, it is almost impossible to meet these demanding criteria. Although large populations exist, collecting sample data from a significantly large enough segment of a population that correctly represents the members of the population is not always feasible. Also, mating is not always random, and there is mixing of populations on a global scale now that leads to “gene flow” on a constant basis. Recently, sequencing of the human genome has revealed that gene mutations occur much more commonly than originally thought. Some of these mutations affect the phenotype of an individual, such as loss of enzyme function, and some do not. Despite these drawbacks, Hardy-Weinberg is still one of the best tools for studying inheritance patterns in human populations and is a cornerstone of population genetics. Most of the various genes controlling the inheritance of blood group antigens can be studied using the Hardy-Weinberg equations. A relevant example that shows how to use the Hardy-Weinberg formula is the frequency of the Rh antigen, D, in a given population. In this simple example, there are two alleles, D and d. To determine the frequency of each allele, we count the number of individuals who have the corresponding phenotype (remembering that both Dd and DD will appear as Rh-positive) and divide this number by the total number of alleles. This value is represented by p in the Hardy-Weinberg equation. Again, counting the alleles lets us determine the value of q. When p and q are added, they must equal 1. The ratio of homozygotes and heterozygotes is determined using the other form of the Hardy-Weinberg equation, p2 + 2pq + q2 = 1. If in our example we tested 1,000 random blood donors for the D antigen and found that

Hardy-Weinberg Principle G. H. Hardy, a mathematician, and W. Weinberg, a physician, developed a mathematical formula that allowed the study of Mendelian inheritance in great detail. The HardyWeinberg formula—p + q = 1, in which p equals the gene frequency of the dominant allele and q is the frequency of the recessive allele—can also be stated p2 + 2pq + q2 = 1 and specifically addresses questions about recessive traits and how they can be persistent in populations (Fig. 2–4). Like

BOX 2–1

Criteria for Use of the Hardy-Weinberg Formula • • • •

The population studied must be large. Mating among all individuals must be random. Mutations must not occur in parents or offspring. There must be no migration, differential fertility, or mortality of genotypes studied.

2682_Ch02_026-044 22/05/12 11:38 AM Page 30

30

PART I

Fundamental Concepts

DD and Dd (Rh-positive) occurred in 84 percent of the population, and dd (Rh-negative) occurred in 16 percent, the gene frequency calculations would be performed as follows: p ⫽ gene frequency of D q ⫽ gene frequency of d p2 ⫽ DD, 2pq ⫽ Dd, which combined are 0.84 q2 ⫽ dd, which is 0.16 q ⫽ square root of 0.16, which is 0.4 p⫹q⫽1 p⫽1⫺q p ⫽ 1 ⫺ 0.4 p ⫽ 0.6

A. Autosomal recessive

Propositus B. X-linked dominant

This example is for a two-allele system only. A three-allele system would require use of the expanded binomial equation p ⫹ q + r ⫽ 1 or p2 ⫹ 2pq ⫹ 2pr ⫹ q2 ⫹ 2qr ⫹ r2 ⫽ 1. More complex examples using this formula can be found in more advanced genetics textbooks.

Inheritance Patterns The interpretation of pedigree analysis requires the understanding of various standard conventions in the representation of data figures. Males are always represented by squares and females by circles. A line joining a male and a female indicates a mating between the two, and offspring are indicated by a vertical line. A double line between a male and a female indicates a consanguineous mating. A stillbirth or abortion is indicated by a small black circle. Deceased family members have a line crossed through them. The propositus in the pedigree is indicated by an arrow pointing to it and indicates the most interesting or important member of the pedigree. Something unusual about the propositus is often the reason the pedigree analysis is undertaken. Figure 2–5 shows examples of different types of inheritance patterns seen in pedigree analysis. Almost all pedigrees will follow one of these patterns or, rarely, a combination of them. The first example is a pedigree demonstrating autosomal-recessive inheritance. Autosomal refers to traits that are not carried on the sex chromosomes. A recessive trait is carried by either parent or both parents but is not generally seen at the phenotypic level unless both parents carry the trait. In some cases, a recessive trait can be genetically expressed in a heterozygous individual but may not be seen at the phenotypic level. When two heterozygous individuals mate, they can produce a child who inherits a recessive gene from each parent, and therefore the child is homozygous for that trait. An example from blood banking is when both parents are Rhtype Dd and have a child who is dd, which is Rh-negative. In the second example, there is a case of a dominant X-linked trait. If the father carries the trait on his X chromosome, he has no sons with the trait, but all his daughters will have the trait. This is because a father always passes his Y chromosome to his sons and his X chromosome to his daughters. Women can be either homozygous or heterozygous for an X-linked trait; therefore, when mothers have an X-linked trait, their daughters inherit the trait in a manner identical to autosomal inheritance. The sons have a 50 percent

C. X-linked recessive

= affected

= affected, heterozygous

= not affected, carrier

Figure 2–5. Schematic illustration of common inheritance patterns.

chance of inheriting the trait. Because the trait is dominant, the sons who inherit it will express it. The Xga blood group system is one of the few blood group systems that follow an X-linked inheritance pattern (refer to Chapter 8). The third example illustrated is X-linked recessive inheritance. In this case, the father always expresses the trait but never passes it on to his sons. The father always passes the trait to all his daughters, who are then carriers of the trait. The female carriers will pass the trait on to half of their sons, who also will be carriers. In the homozygous state, X’Y, the males will express the trait, whereas only the rare homozygous females, X’X’, will express it. In this situation, with an X-linked recessive trait, a disease-carrying gene can be passed from generation to generation, with many individuals not affected. A classic example of this is the inheritance of hemophilia A, which affected many of the royal houses of Europe. In addition, there is autosomal-dominant, in which all the members of a family who carry the allele show the physical characteristic. Generally, each individual with the trait has at least one parent with the trait, and the gene is expressed if only one copy of the gene is present. Unlike X-linked traits, autosomal traits usually do not show a difference in the distribution between males and females, and this can be a helpful clue in their evaluation. Also, in autosomal and X-linked

2682_Ch02_026-044 22/05/12 11:38 AM Page 31

Chapter 2 Basic Genetics

traits, if an individual does not have the trait, he or she can be a carrier and can pass it on to offspring. This is why recessive traits seem to skip generations, which is another helpful clue in determining inheritance patterns. Autosomal-dominant traits are routinely encountered in the blood bank, as most blood group genes are codominant and are on autosomal chromosomes. They are passed on from one generation to the next and do not skip generations; therefore, they are usually present in every generation. Finally, unusually rare traits that occur in every generation and in much greater frequency than the general population are often the result of matings between related individuals. Table 2–1 provides examples of inheritance patterns in transfusion medicine.

Cellular Genetics Organisms may be divided into two major categories: prokaryotic, without a defined nucleus, and eukaryotic, with a defined nucleus. Human beings and all other mammals are included in the eukaryotic group, as are birds, reptiles, amphibians, fish, and some fungus species. The nucleus of a cell contains most of the genetic material important for replication and is a highly organized complex structure. The nuclear material is organized into chromatin, consisting of nucleic acids and structural proteins, and is defined by staining patterns. Heterochromatin stains as dark bands, and achromatin stains as light bands and consists of highly condensed regions that are usually not transcriptionally active. Euchromatin is the swollen form of chromatin in cells, which is considered to be more active in the synthesis of RNA for transcription. Most cellular nuclei contain these different types of chromatin. The chromatin material itself, which chiefly comprises long polymers of DNA and various basic proteins called histones, is compressed and coiled to form chromosomes during cell division. Each organism has a specific number of chromosomes, some as few as 4 and some as many as 50. In humans, there are 46 chromosomes. These 46 chromosomes are arranged into pairs, with one of each being inherited from each parent. Humans have 22 autosomes and one set of sex chromosomes, XX in the female and XY in the male. This comprises the 2N state of the cell, which is normal for all human cells except the gametes (sex cells). N refers to the number of pairs of chromosomes in a cell.

Table 2–1 Examples of Inheritance Patterns in Transfusion Medicine TYPE OF PATTERN

EXAMPLE

Autosomal-dominant

In (Lu) suppressor gene

Autosomal-recessive

dd genotype

X-linked dominant

Xga blood group system

X-linked recessive

Hemophilia A

31

Terminology Remember that it takes two gametes to make a fertilized egg with the correct (2N) number of chromosomes in the nucleus of a cell. Therefore, each parent contributes only half (1N) of the inherited genetic information, or genes, to each child. In order to be completely healthy, each child must have the correct number of genes and chromosomes (2N), without major mutations affecting necessary biochemical systems. The genetic material has a complex pattern of organization that has been evolving for millions of years to an amazing level of coordination and control. At the smallest level, genes are composed of discrete units of DNA arranged in a linear fashion, similar to a strand of pearls, with structural proteins wrapped around the DNA at specific intervals to pack it into tightly wound bundles. The DNA is organized at a higher level into chromosomes, with each chromosome being one incredibly long strand of duplex (double-stranded) DNA. A gene is a section, often very large, of DNA along the chromosome. The specific sequence of nucleotides and the location on the chromosome determines a gene. In addition, each gene has specific and general sequences that occur upstream (before the start site) and downstream (after the termination signals) that contribute to how the gene functions. The specific location of a gene on a chromosome is called a locus (plural = loci), and at each locus there may be only one or several different forms of the gene, which are called alleles. It is important to keep in mind the distinction between phenotype and genotype. Genotype is the sequence of DNA that is inherited. The phenotype is anything that is produced by the genotype, including an enzyme to control a blood group antigen; the length of long bones of the skeleton; the curvature of the spine; the ratio of muscle fibers; the level of hormones produced; and such obvious traits as eye, skin, and hair color. Keep in mind that more than one gene can affect a particular trait (part of a phenotype), such as the height of an individual; all relevant genes can be considered as part of the genotype for that trait. Depending on the alleles inherited, an organism can be either homozygous or heterozygous for a specific trait. The presence of two identical alleles results in a homozygous genotype (i.e., AA), and the phenotype is group A blood. On the other hand, the inheritance of different alleles from each parent gives a heterozygous genotype. Another important concept is that of the “silent” gene, or amorph, and the term hemizygous. An amorph is a gene that does not produce any obvious, easily detectable traits and is seen only at the phenotypic level when the individual is homozygous for the trait. Hemizygous refers to the condition when one chromosome has a copy of the gene and the other chromosome has that gene deleted or absent.

Mitosis During cell division, the chromosomes are reproduced in such a way that all daughter cells are genetically identical to the parent cell. Without maintaining the same number and type of chromosomes, the daughter cells would not be viable. The process by which cells divide to create identical daughter

2682_Ch02_026-044 22/05/12 11:38 AM Page 32

32

PART I

Fundamental Concepts

cells is called mitosis. The chromosomes are duplicated, and one of each pair is passed to the daughter cells. During the process of mitosis, quantitatively and qualitatively identical DNA is delivered to daughter cells formed by cell division. The complex process of mitosis is usually divided into a series of stages, characterized by the appearance and movement of the chromosomes. The stages are interphase, prophase, metaphase, anaphase, and telophase. The different phases of mitosis include interphase at the beginning, in which DNA is in the form of chromatin and is dispersed throughout the nucleus. This is the stage of the DNA when cells are not actively dividing. New DNA is synthesized by a process called replication. In the next stage, prophase, the chromatin condenses to form chromosomes. In prophase, the nuclear envelope starts to break down. In the next stage, metaphase, the chromosomes are lined up along the middle of the nucleus and paired with the corresponding chromosome. In this stage, chromosome preparations are made for chromosome analysis in cytogenetics. In anaphase, which occurs next, the cellular spindle apparatus is formed and the chromosomes are pulled to opposite ends of the cell. The cell becomes pinched in the middle, and cell division starts to take place. In the last stage, telophase, the cell is pulled apart, division is complete, and the chromosomes and cytoplasm are separated into two new daughter cells. The process of mitosis is illustrated in Figure 2–6 and outlined in Table 2–2.

Mitosis

2N

Prophase

MITOSIS Stage

Description

1. Interphase (2N)

Resting stage between cell divisions; during this period, cells are synthesizing RNA and proteins, and chromatin is uncondensed.

2. Prophase (4N)

First stage of mitotic cell division. Chromosomes become visible and condense. Each chromosome has two chromatids from duplication of DNA, and chromatids are linked via the centromere.

3. Metaphase (4N)

Chromosomes move toward the equator of the cell and are held in place by microtubules attached at the mitotic spindle apparatus.

4. Anaphase (4N)

The two sister chromatids separate. Each one migrates to opposite poles of the cell, and the diameter of the cell decreases at equator.

5. Telophase (2N)

Chromosomes are at the poles of the cell, and the cell membrane divides between the two nuclei. The cell divides, and each cell contains a pair of chromosomes identical to the parent cell.

MEIOSIS Stage

Description

1. Interphase (2N)

Resting stage between cell divisions; during this period, cells are synthesizing RNA and proteins, and chromatin is uncondensed.

2. Prophase I (4N)

First stage of meiotic division. Chromosomes condense. Homologous chromosomes pair to become bivalent. Chromosome crossing over occurs at this stage.

3. Metaphase I (4N)

Bivalent chromosomes align at cell equator. Bivalent chromosomes contain all four of the cell’s copies of each chromosome.

4. Anaphase I (4N)

Homologous pairs move to opposite poles of the cell. The two sister chromatids separate.

5. Telophase I (2N)

The cell separates to become two daughter cells. The new cells are now 2N.

6. Metaphase II (2N)

Homologues line up at the equator.

7. Anaphase II (N)

Homologues move to opposite poles of the cell equator.

8. Telophase II (N)

Each cell separates into two new cells. There are now four (N) cells with a unique genetic constitution.

4N

Metaphase

4N

Anaphase

4N

Telophase and cell division 2N

Table 2–2 Stages of Mitosis and Meiosis

Meiosis 2N

Figure 2–6. Mitosis leads to two daughter cells having the same number of chromosomes as the parent cell.

A different process is used to produce the gametes or sex cells. The process is called meiosis and results in four unique, rather than two identical, daughter cells. The uniqueness of the daughter cells generated with meiosis

2682_Ch02_026-044 22/05/12 11:38 AM Page 33

Chapter 2 Basic Genetics

allows for great genetic diversity in organisms and controls the number of chromosomes within dividing cells. If cells with 2N chromosomes were paired, the resulting daughter cells would have 4N chromosomes, which would not be viable. Therefore, gametes carry a haploid number of chromosomes, 1N, so that when they combine, the resulting cell has a 2N configuration. Meiosis only occurs in the germinal tissues and is important for reproduction. Without the complicated process of meiosis, there would be no change from generation to generation, and evolution would not occur or happen too slowly for organisms to adapt to environmental changes. The first stages of meiosis are nearly identical to those in mitosis, in which chromatin is condensed, homologous chromosomes are paired in prophase, and chromosomes are aligned along the center of the cell. However, there is no centromere division, and at anaphase and telophase, the cell divides and enters once again into interphase, in which there is no replication of DNA. This is followed by the second prophase, in which chromosomes are condensed, and then the second metaphase, with the centromeres dividing. Finally, in the second anaphase and telophase stages, the two cells divide, giving rise to four 1N daughter cells. In addition, during meiosis, crossing over and recombination can happen between maternal- and paternal-derived chromosomes. This allows for the creation of new DNA sequences that are different from the parent strains. Combined with random segregation, it is possible to have very large numbers of new DNA sequences. In humans with 23 pairs of chromosomes, the total possible number is several million. Meiosis is illustrated in Figure 2–7 and outlined in Table 2–2.

Meiosis

2N

Prophase I

4N

Metaphase I

4N

Anaphase I

4N

2N

Telophase I and cell division

2N

2N

Metaphase II

2N

Cell Division

Telophase II and cell division

Gametes

Cell division is also a complicated process and one that is important to understand. It also occurs with various specific stages. In eukaryotic cells such as human cells, the cell cycle is divided into four distinct stages and is represented by a clock or circular scheme indicating that it can repeat itself or can be stopped at any one point in the cycle. The first step or stage is the resting stage, or G0, and is the state of cells not actively dividing. The prereplication stage is next and is called G1. The step at which DNA is synthesized is the next stage, called the S stage. It is followed by the G2 stage, or postreplication stage. Finally, there is the M phase, in which mitosis occurs. Chromosomes are in the interphase stage of mitosis in the span from G0 to the end of the G2 phase. Cells that are completely mature and no longer need to divide to increase their numbers, such as nerve cells, can remain in the G0 stage for a very long time. It is a hallmark of cancer cells, such as the transformed cells seen in the various leukemias and solid tumors, that they can go through the stages of cell division much faster than nontransformed, normal cells and therefore outgrow them. In this way, they take up the bulk of nutrients needed by the nontransformed cells and crowd them out of existence and potentially overgrow the adult organism in which they occur (Table 2–3).

33

N

N

N

N

Figure 2–7. Meiosis produces four gametes having half the number of chromosomes present in the parent cell.

Table 2–3 The Generative Cell Cycle STAGE

DESCRIPTION

CONFIGURATION

G0 (Gap 0)

Temporary resting period, no cell division

2N

G1 (Gap 1)

Cells produce RNA and synthesize protein

2N

S (Synthesis)

DNA replication occurs

4N

G2 (Gap 2)

During the gap between DNA synthesis and mitosis, the cell continues to synthesize RNA and produce new proteins

4N

M (Mitosis)

Cell division occurs

2N

2682_Ch02_026-044 22/05/12 11:38 AM Page 34

34

PART I

Fundamental Concepts

Molecular Genetics The study of genetics at the molecular level requires an understanding of the biochemistry of the molecules involved. This includes knowledge of the physical conformation of chromosomes as well as the biological and chemical nature of the polymers of the different nucleic acids and nuclear proteins.

Deoxyribonucleic Acid Deoxyribonucleic acid (DNA) is a masterpiece of architectural evolution and the “backbone” of heredity. Chromatin is actually a type of polymer structure. Chromosomes are composed of long, linear strands of DNA tightly coiled around highly basic proteins called histones (Fig. 2–8). Each chromosome is a single, extremely long strand of duplex DNA. Remember that DNA is a nucleic acid, and therefore most of the proteins that interact with it have an overall basic pH. This helps to stabilize the overall complex structure. The complex of DNA and histone protein is referred to as a nucleosome. The DNA and protein complex is bound together so tightly and efficiently that extremely long stretches of DNA, several inches in length, can be packaged inside the nucleus of a cell on a microscopic level. The DNA and histones are held together by various proteins that keep the DNA in a very specific helical conformation. This conformation also protects the DNA from degradation when it is not being replicated or transcribed. All DNA in human cells is in the form of a two-stranded duplex, with one strand in one direction and its complementary strand in the opposite direction (the strands are said to be antiparallel). DNA is composed of four nitrogenous bases, a 5-carbon sugar molecule called deoxyribose and a phosphate group. The sugar and phosphate moieties comprise the backbone of the DNA molecule, while the nitrogenous bases face in to each other and are stabilized by hydrogen bonding and Van der Waals forces. The backbone of a DNA molecule is joined by phosphodiester linkages. Unlike what is observed in proteins with an ␣-helical structure, there is little bonding forces between bases on the same strand, which allows DNA to be strong but flexible.

The four different bases are adenine (A), cytosine (C), guanine (G), and thymine (T). Adenine and guanine are purines, consisting of double-ring structures. Cytosine and thymine are pyrimidines, which are single-ring structures (Fig. 2–9). The hydrogen bonding in DNA is specific, in which A bonds only to T with two hydrogen bonds, thus forming the weaker pairing, and C bonds only with G with three hydrogen bonds, forming the stronger pairing. This is the classic Watson-Crick base pairing that occurs in the B-form, right-handed helical structure of DNA. It was first postulated by James Watson and Francis Crick, at Cambridge University in the early 1950s (Fig. 2–10).1 Since then, it has been discovered that DNA can also occur in modified forms such as Z-DNA, which is a type of left-handed helix with a different three-dimensional conformation but that contains the same four nitrogenous bases.2 In addition, there are some unusual forms of nitrogenous bases that can be incorporated into DNA templates. The phosphates in the DNA backbone attach to the sugar at the third and fifth carbon atoms. Remember, all atoms in a molecular structure are numbered. The linkage of the purine or pyrimidine nitrogenous base to the sugar is at carbon 1. Therefore, the two DNA strands are antiparallel—that is, one strand is 5′ to 3′ (pronounced “5 prime to 3 prime”) in one direction and the complementary strand is 5′ to 3′ in the other direction. During transcription, only one strand is copied, which is the complementary strand that gives the correct 5′ to 3′ sequence of messenger RNA (mRNA) that corresponds to the template, or coding strand, of the DNA molecule. As there are only four different bases used to make up DNA templates and there are 20 different amino acids that are used to construct proteins, it is evident that any single nucleotide cannot code for any specific amino acid. What has been discovered is that triplets of nucleotides called a Thymine—Adenine

deoxyribose

DNA

HISTONES

DNA

deoxyribose Cytosine—Guanine

deoxyribose deoxyribose

Figure 2–8. Nucleosomes consist of stretches of DNA wound around histone proteins.

Dotted lines represent interatomic hydrogen bonds, which hold the base pairs together. Figure 2–9. The pyrimidine and purine bases found in the DNA molecule.

2682_Ch02_026-044 22/05/12 11:38 AM Page 35

Chapter 2 Basic Genetics

The genetic code is triplet

The double helix has constant width

First base

U UUU

U

UUC UUA UUG CUU

C

CUC CUA CUG

Figure 2–10. Base pairing in DNA and DNA structure. (From Lewin B: Genes VIII. Prentice Hall/Pearson Education, New York, 2004, p 6. Reprinted with permission of the author.)

AUU

A

AUC AUA AUG

codon, such as ATG, code for one specific amino acid. However, there is a redundancy to the genetic code in that some amino acids have more than one triplet, which codes for their addition to the peptide chain formed during translation. Generally, the more common the amino acid is in proteins, the greater the number of codons it has. There are four special codons, including the only codon specific for the initiation of transcription and translation, called the start codon, and three different codons that are used to stop the addition of amino acids in the process of peptide synthesis. Because these three codons cannot be charged with an amino acid, they are called stop codons and result in termination of the peptide being translated from mRNA. The genetic code is illustrated in Figure 2–11. Replication The replication, or copying, of DNA is a complex process involving numerous enzymes, nucleic acid primers, various small molecules, and the DNA helix molecule that serves as its own template for the replication process. DNA must be copied before mitosis can occur and must be copied in such a way that each daughter cell will have the same amount of DNA and the same sequence. Nearly all DNA replication is done in a bidirectional manner and is semiconservative in nature.3 Specifically, as enzymes involved in the replication process open the double-stranded DNA helix, one strand of DNA is copied in a 5′ to 3′ manner, while the other strand is opened partially in sections and is copied 5′ to 3′ in sections as the double-stranded template continuously opens. In addition, each newly synthesized DNA strand will be paired with one of the parent strands. The replication process is shown in Figure 2–12. In order for DNA to be replicated with the exact copying of the template and its sequence into a new double-stranded helix, many enzymes and proteins must participate in the process. DNA replication occurs in specific steps, and certain

35

GUU

G

GUC GUA GUG

Second base

C

} }

} } } } } } } Phe Leu

Leu

UCU

UAU

UCC

UAC

UCA

Val

UAA UAG

CCU

CAU

CCC

CAC

Pro

CAG

ACU

AAU

ACC

AAC

Thr

AAA

ACG

AAG

GCU

GAU

GCC

GAC

Ala

G

} }

CAA

CCG

ACA

Met

Ser

UCG

CCA

Ile

A

GCA

GAA

GCG

GAG

Tyr

UGC

STOP

} } } } } }

UGU

}

UGA STOP UGG

His Gln

Asn Lys

Asp

CGU CGC CGA CGG AGU AGC AGA AGG

GGU GGC

Glu

Cys

GGA GGG

Trp

} } }

}

Arg

Ser Arg

Gly

Figure 2–11. The genetic code. (From Lewin B: Genes VIII. Prentice Hall/Pearson Education, New York, 2004, p 168. Reprinted with permission of the author.)

enzymes and other molecules are required at each step. First, sections of DNA must be uncoiled from its supercoiled (or double-twisted) nature, and the two strands must be separated and kept apart; this is done by the enzymes DNA gyrase (opens the supercoils) and DNA helicase (separates the two strands of duplex DNA). These enzymes, using energy derived from ATP hydrolysis, open the DNA molecules and keep the strands separate. In the next step, DNA polymerase III can synthesize a new strand in the 5′ to 3′ direction on the leading strand. Proteins called single-stranded binding proteins interact with the open strands of DNA to prevent hydrogen bonding when it is not needed during replication. DNA polymerase III also proofreads the addition of new bases to the growing DNA strands and can remove an incorrectly incorporated base, such as G paired to T. In order for replication to take place on any piece of DNA, there must first be a short oligonucleotide (composed of RNA) piece that binds to the beginning of the region to be replicated. This “primes” the replication process; therefore, these short oligonucleotide sequences are called primers. All DNA is replicated in a 5′ to 3′ manner. Replication of the other parent strand, the lagging strand, is more complicated because of this restriction. As the helix is opened, RNA primer sequences are added to the area of the opening fork, and the RNA primers are extended in a 5′ to 3′ manner until

2682_Ch02_026-044 22/05/12 11:38 AM Page 36

36

PART I

Fundamental Concepts

The two new DNA strands have different features Leading strand synthesis Nucleotides added continuously to 3’ end 3’ 5’

5’

Leading strand

3’

3’

Lagging strand

5’ Lagging strand synthesis Parental DNA

Single strand

Last fragment

Previous fragment

Figure 2–12. DNA replication.

the polymerase reaches the previously synthesized end. Rather than being replicated in a continuous manner, these replication forks open up all along the lagging strand and are extended in this way. These small regions of newly replicated DNA are known as Okazaki fragments. The fragments must be joined together to make a complete and continuous strand. This is accomplished by the two enzymes DNA polymerase I and DNA ligase. The RNA primers are synthesized and added to the DNA strands by an enzyme called primase, which anneals to the parent strands. After replication of the leading and lagging strands is complete, DNA ligase joins the phosphodiester bonds of the DNA backbone to complete the intact molecule. Isomerase enzymes recoil the DNA; once this is completed and the DNA is proofread by proofreading enzymes, the cell can continue with mitosis and cell division. Repair DNA must be copied exactly or the information it contains will be altered, possibly resulting in a decrease in the organism’s vitality. However, mistakes in the complex process of replication do occasionally occur, and a number of efficient mechanisms have evolved to correct these mistakes. The mechanisms can detect the mistakes, or changes, and correct the actual DNA sequence. One of the most important mechanisms for correcting DNA replication errors is the proofreading ability of DNA polymerases. The proofreading occurs in both the 5′ to 3′ and 3′ to 5′ directions and allows the polymerase to backtrack on a recently copied DNA strand and remove an incorrect nucleotide and insert the correct one in its place. In addition to the proofreading ability of DNA polymerase enzymes, there is a second type of editing called mismatch repair, where an incorrect nucleotide is removed and the correct one is inserted in its place. In addition to errors in the primary nucleotide sequence of DNA molecules, there are other possible alterations that can affect the way the sequence information is processed. Many different chemicals and environmental factors can alter DNA by modifying it chemically or physically. These include alkylating agents, which react with guanine and result in

depurination. Some cancer treatments are often based on this principle that the faster-replicating DNA in cancer cells has greater damage and puts cancer cells at greater risk for cell death than normal cells. Ionizing radiation and strong oxidants such as peroxides can cause single-strand breaks. Ultraviolet (UV) radiation can alter thymine bases, resulting in thymine dimers. Certain drugs such as the antibiotic mitomycin C can form covalent linkages between bases on opposite strands; therefore, during replication, separation of the strands at that site will not occur correctly, and the resulting daughter strands will have mutations. Nearly all defects in DNA replication can be corrected by the various mechanisms used by the cell to maintain DNA integrity. However, if too many mistakes occur, the repair systems can be overwhelmed, and mistakes will not be corrected. The cell in which these mutations occur will have an altered DNA nucleotide sequence and may or may not be viable. There are several major DNA repair systems. These include photoreactivation, excision repair (also referred to as cut and patch repair), recombinational repair, mismatch repair, and SOS repair (Box 2–2). DNA repair systems can recognize mismatched base pairs, missing nucleotides, and altered nucleotides in DNA sequences. For example, when thymine dimers are formed after exposure to UV light, the photoreactivation enzyme becomes active and enzymatically cleaves the thymine dimers. In addition to the photoreactivation system of DNA repair, thymine dimers can be removed by the rather complex process of excision repair, where the disrupted section of the DNA is removed. A cut is

BOX 2–2

DNA Repair Systems • • • • •

Photoreactivation Excision repair Recombinational repair Mismatch repair SOS repair

2682_Ch02_026-044 22/05/12 11:38 AM Page 37

Chapter 2 Basic Genetics

made on one side of the thymine dimer that bulges out from the rest of the duplex DNA. DNA polymerase I synthesizes a short replacement strand for the damaged DNA section. The old strand is removed by DNA polymerase I as it moves along the DNA. Finally, the old DNA strand is removed, and the newly formed DNA segment is ligated into place. Recombinational repair uses the correct strand of DNA to fill in the strand where the error was deleted. Polymerase I and DNA ligase, then fill in the other strand. Mismatch repair is activated when base pairing is incorrect and a bulge occurs in the duplex DNA. Mismatch repair enzymes are able to remove the incorrect nucleotides and insert the correct ones. Methyl groups on adenines are used by the mismatch enzyme systems to determine which nucleotide is correct and which is a mistake. When DNA and cell damage occurs, SOS repair is induced. Damage can be caused by UV radiation, chemical mutagens, and excessive heat, and by such treatments as exposure to cross-linking agents. There are certain sections of highly conserved DNA that are activated when DNA is damaged, and the genes that are part of the SOS response system must work in a coordinated manner to repair the damaged DNA through recombination events that remove the damaged sections and replace them with the correct sequences. Repair systems exist and have been studied closely in both prokaryotes and eukaryotes. All of these systems are available to maintain the integrity of the DNA. The fact that so many repair systems exist in the cell proves how important the correct structure and sequence of DNA is to the cell. It also shows how complex the DNA molecule is in that many types of mutations can occur, and therefore many types of correction processes are present to repair them. Mutations Although many effective DNA proofreading and repair systems help to keep newly synthesized DNA from having mutations, none of the systems are foolproof and occasional mutations occur. Once a mutation is introduced into a DNA coding strand, the information in that strand is now altered. It may be altered at the protein level if the mutation encodes for a different amino acid or a change in reading frame. In general, a mutation is any change in the structure or sequence of DNA, whether it is physical or biochemical. An organism is referred to as a mutant if its DNA sequence is different from that of the parent organism. The original form of the DNA sequence, and the organism in which it occurs, is called the wild type. The various chemicals and conditions that can cause mutations are referred to as mutagens. Many mutagens are also carcinogens in that the cells in which they occur have an advantage in growth patterns that allows them to dominate the cells around them. There are different types of mutations, and they may have very different consequences for the organisms in which they occur. Also, remember that mutations can be spontaneous. If they occur in the germinal tissue, they are passed on from one generation to the next. The simplest type of mutation is the point mutation, in which only one nucleotide in the DNA sequence is changed. Point mutations include substitutions, insertions, and deletions. Certain substitutions,

37

although they change the DNA sequence and the triplet codon(s), may not change the amino acid sequence in the corresponding protein because of redundancy in the genetic code. Recall that some of the amino acids have more than one codon that represents them. Therefore, if the new codon is for the same amino acid, the mutation will be silent, and the protein sequence will be the same. An example of this is the amino acid threonine, which has ACA, ACC, ACG, and ACU as possible codons. Therefore, a substitution of C, G, or U for A at the third position of the codon would still have a peptide with threonine at that position. A type of “silent mutation” also occurs when a mutation happens that causes a change in the peptide sequence, but that part of the peptide does not seem critical for its function; therefore, no mutation is seen at the phenotypic level, such as enzyme function or cell surface marker. A transition is a type of mutation in which one purine is substituted for another purine, or one pyrimidine is substituted for another pyrimidine. When a purine is substituted for a pyrimidine or a pyrimidine for a purine, it is called a transversion. Examples of DNA mutations are outlined in Table 2–4.4 Another type of mutation that can have a deleterious effect on the peptide sequence is called a missense point mutation. A missense mutation results in a change in a codon, which alters the amino acid in the corresponding peptide. These changes cannot be accommodated by the peptide while still maintaining its function. Typical examples of missense mutations include the alterations in the hemoglobin molecule at a single base pair, resulting in different types of inherited anemias.5 A very specific type of serious mutation, called a nonsense mutation, results when a point change in one of the nucleotides of a DNA sequence causes one of the three possible stop codons to be formed. The three stop codons are amber (UAG), opal (UGA), and ochre (UAA), and these terminate the reading of the DNA sequence, so the resulting peptide is truncated at its 3′ end. A more severe type of mutation happens when there is an insertion or deletion of one or more (but never multiplicities of three) nucleotides in the DNA sequence. The result of this

Table 2–4 Examples of DNA Mutations in Blood Groups TRANSITION S antigen

s antigen

Amino acid

Methionine

Threonine

mRNA code

AUG

ACG

DNA code

TAC

TGC

TRANSVERSION N antigen

He antigen

Amino acid

Leucine

Tryptophan

mRNA code

UUG

UGG

DNA code

AAC

ACC

2682_Ch02_026-044 22/05/12 11:38 AM Page 38

38

PART I

Fundamental Concepts

type of mutation is a change in the triplet codon sequence and therefore an alteration in the frameshift reading so that a large change in the amino acid sequence occurs. Remember that the DNA sequence is read three nucleotides at a time, called codons, and each codon can be charged with a specific amino acid. In transfusion medicine, it has been shown that there is a single base pair deletion in the gene encoding for the transferase protein of the A blood group.6 The frameshift mutation results in a nonfunctional transferase protein that is seen phenotypically as the O blood group. Unusual genetic changes can also happen that cause gross mutations in the DNA sequence. Duplications, recombinations, and large deletions have a lower frequency rate than the mutations in the replication of DNA noted above. Duplications can occur quite frequently and give rise to pseudogenes and other so-called junk DNA that does not code for proteins. A large part of DNA consists of such junk DNA without apparent ill effects and may even be necessary to some extent for the structural integrity of DNA and chromosomes. Also, there are sequences “left over” from earlier evolution that are still present in human DNA, such as Alu sequences. In addition, there may be evolutionary pressures forcing duplications to occur. DNA contains short tandem repeats of various lengths throughout the entire DNA molecule. In blood banking, there are two good examples of duplications. The first involves the glycophorin A and B genes; the second involves the genes RHD and RHCE. The Chido and Rodgers blood group antigens, carried on the complement components of the C4A and C4B genes, arose from duplications and mutations of the C4 genes (refer to Chapter 8). In addition to these mutations, exchanges occasionally occur between chromosomes, such as the Philadelphia chromosome present in myelogenous leukemia. Mutations involving recombination or crossing over take place during the process of meiosis in the formation of gametes. It is very important to generate sex cells that are different from the parental cells. Recombination involves breaking both double-stranded DNA homologues, exchanging both strands of DNA, and then resolving the new DNA duplexes by reconnecting phosphodiester bonds. Crossing over can be single, double, or triple events (Fig. 2–13). An example of such an event resulting in a hybrid formation is seen in the MNSs blood group system. Crossover events have formed the genes for the Dantu and Mi V blood groups. One of the most important events in the immune system is the recombination of the D, V, and J genes, which gives rise to the vast array of immunoglobulin genes that are necessary to form the antibodies of the humoral system. Deletion of large segments of DNA sequences covering hundreds and possibly even thousands of nucleotides is also possible. It is a type of mutation that is not capable of being corrected by any of the DNA repair systems due to the size and complexity of the mutation. Such mutations can result in complete loss of a peptide, a severely truncated peptide, or the formation of a nonfunctional peptide. An example of this type of mutation in transfusion medicine is the Rodgers negative phenotype, which results from a 30 kD deletion of both the complete CD4 (Rodgers) and 21-hydroxylase genes.7

Crossing-over occurs at the 4-strand stage

Figure 2–13. Crossing over of DNA strands and chiasma formation to create new sequences. (From Lewin B: Genes VIII. Prentice Hall/Pearson Education, New York, 2004, p 20. Reprinted with permission of the author.)

Isolation The ability to successfully isolate DNA from cell cultures, blood, and other clinical specimens is fundamental to optimal performance of other molecular procedures described in Chapter 4. Common methods used for the isolation of nucleic acids use alkaline denaturation and precipitation with alcohol and high salt concentrations. They can be further purified from other unwanted cellular components, such as the cytoplasmic membrane, by use of specific columns or beads that will bind nucleic acids based on charge-charge interactions. Magnetic bead technology has become an efficient and popular way to isolate DNA and other molecules or even specific cell types, and it can be automated. Column chromatography has been in use for many years, and different materials are used to prepare columns, depending on the nature of the materials to be separated. In more traditional methods, DNA was isolated after treatment of cells with harsh mechanical or chemical agents often necessary to break open cell walls and disrupt proteins and fatty acids. Sonication, phenol, and chloroform, or various chaotropic agents were used to disrupt cells, then followed by highspeed centrifugation on cesium chloride or sucrose gradients to isolate the nucleic acids. This was necessary to separate the high and low molecular weight DNA and RNA molecules within the cell. RNA requires greater care than DNA, as it is a single-stranded molecule and much more labile. Chemicals that will inactivate RNase enzymes must be used to obtain RNA that is not readily degraded and has its sequence intact. As mRNA is only a small part of the total RNA isolated, it can be purified by nature of its poly-A tail using a column that contains poly-T attached to resin bead molecules. Methods such as complementary DNA (cDNA) synthesis, in which RNA is converted into a DNA copy in vitro, allows

2682_Ch02_026-044 22/05/12 11:38 AM Page 39

Chapter 2 Basic Genetics

greater study of RNA sequences by making a more stable version of it. RNA isolation also requires greater disruption of the cellular material, usually with chaotropic agents such as guanidine thiocyanate, lithium salts, and mechanical means to disrupt cell membranes, such as douncing or shearing with a needle and syringe. Once DNA or RNA has been isolated, they can be stored in low salt buffers at the respective correct pH at –20°C or lower for DNA and RNA at –80°C for many months to many years. Storage in water is not recommended because the nucleic acids are polymers, hydrolysis reactions will degrade them, and water can contain contaminates that can degrade nucleic acids over time, even at low temperatures. Important is the pH of the buffer used in nucleic acid isolation and storage, as acidic pH can result in degradation of DNA and alkaline pH can degrade RNA.

Ribonucleic Acid Ribonucleic acid (RNA) is similar to DNA in structure but has certain key differences. It has a very different role to play in the cell. One of the key structural differences is that unlike DNA, which is usually a double-stranded helix, RNA occurs most often as a single-stranded structure, although internal hydrogen bonding occurs frequently, probably to stabilize the RNA molecules. Both DNA and RNA are made up of nucleotides, but in place of thymine in DNA there is uracil in RNA. Uracil is very similar to thymine except that it lacks a methyl group. Another major difference is the substitution of the sugar ribose for deoxyribose in the backbone structure. The sugar in DNA, deoxyribose, lacks a hydroxyl group (-OH) at the 2′ carbon position (thus, the deoxyribonucleic acid, or DNA, name). Ribose in RNA has the hydroxyl group at this carbon position, whereas DNA has hydrogen. In eukaryotes, RNA used to transmit genetic information (stored as DNA) from the nucleus to the cytoplasm is translated into peptides and proteins. DNA is copied into RNA by transcription, modified and transported out of the nucleus to the ribosomes, where it is translated into protein, which is then modified if necessary for its proper function. Therefore, RNA is the “go-between” of DNA, which stores genetic information and protein, which is the final product of the expression of that genetic information. It is worth mentioning that certain viruses can store genetic information as RNA, whereas others use DNA, either single- or double-stranded; some viruses use both during the different parts of their infectious cycles. In eukaryotes there are four major types of RNA; each has a specific function as well as its own corresponding polymerase. The first class of RNA molecule is ribosomal RNA (rRNA), which makes up a large part of the ribosomal structure on the endoplasmic reticulum in the cytoplasm. It is here that RNA is translated into peptide. RNA polymerase I transcribes rRNA. It is the most abundant and consistent form of RNA in the cell. The second class of RNA is messenger RNA (mRNA); it is this form that is transcribed from DNA that encodes specific genes, such as those determining the various blood groups. RNA polymerase II transcribes mRNA. Unlike rRNA, mRNA molecules are very different

39

from each other, depending on the gene they were transcribed from. In addition, mRNA undergoes postsynthesis processing before it can be transferred out of the nucleus and translated. The third major class of RNA is transfer RNA (tRNA); it is involved in bringing amino acids to the mRNA bound on the ribosome. Each tRNA molecule can be charged with only one species of amino acid. However, as mentioned, the genetic code is redundant, and many amino acids have more than one type of tRNA that codes for them. In addition, tRNA has considerable internal hydrogen bonding to acquire its formal structure. This hydrogen bonding stabilizes tRNA as well. The fourth major type of RNA includes small RNA molecules, which have other various functions within the cell. These RNA molecules, such as silencing RNA molecules, are necessary for proper gene expression and are altered in amount and type during cellular growth and differentiation. Transcription Transcription is the cellular process by which DNA is copied into RNA. Although mRNA accounts for only a small percent of the total RNA inside a eukaryotic cell, it has the extremely important role of being a “transportable” and disposable form of the genetic code. Messenger RNA allows for highly efficient processing of the genetic code into the proteins that play nearly all the functional roles within a cell. Transcription begins when the enzyme RNA polymerase II binds to the region upstream (to the left of the 5’ start site) of a gene. Certain DNA short sequences, called consensus sequences, such as the CAAT box and TATA box, are located at specific sections upstream of the gene to be transcribed; these are used to position RNA polymerase properly so transcription of a gene is started correctly. This region is referred to as the promoter and is important in how and when a gene is expressed. Promoter regions also contain specific sequences that allow certain proteins, transcription factors, to bind to them preferentially. This allows for certain genes to be more or less active than other genes. Transcription factors are very critical to proper cell growth and differentiation. Upstream sequences are not part of the mRNA itself and are never transcribed; rather, they function to control transcription of mRNA. In addition to the promoter regions that can positively or negatively regulate various transcription factors and other transcription-specific protein effectors, there are regions of DNA sequence called enhancers that can affect transcription rates. Unlike promoters, these enhancer regions can have such effects without being close to the coding regions of the genes they influence. RNA is synthesized in a 5′ to 3′ direction; transcription starts at the 3′ end of the coding (or template) strand of the DNA duplex after it is opened to two single strands and proceeds to the 5′ end. In this way, a 5′ to 3′ coding strand is generated with U in place of T. The RNA transcript is complementary to the template strand and is equivalent to the coding strand of the DNA molecule. Transcription is illustrated in Figure 2–14.

2682_Ch02_026-044 22/05/12 11:38 AM Page 40

40

PART I

Fundamental Concepts

One strand of DNA is transcribed into RNA

Eukaryotic mRNA is modified and exported

5' TACGCGGTACGGTCAATGCATCTACCT 3' ATGCGCCATGCCAGTTACGTAGATGGA

5' UACGCGGUACGGUCAAUGCAUCUACCU

Figure 2–14. Transcription of RNA from DNA. (From Lewin B: Genes VIII. Prentice Hall/Pearson Education, New York, 2004, p 241. Reprinted with permission of the author.)

After RNA is transcribed, it is further processed before it is transported to the ribosome and translated into protein. One major modification to eukaryotic mRNA is the 5′ 7-methyl guanosyl cap that is added to protect the mRNA from degradation by nucleases. The 3′ end of mRNA is modified by the addition of a string of adenines that form a polyadenylation signal (poly-A tail), which can vary in length from about 20 to 200 nucleotides and is believed to increase mRNA stability. In addition to these steps, eukaryotic mRNA has intervening sequences called introns that do not code for protein or peptide and must be removed before translation can begin. The process by which introns are removed from mRNA is called RNA splicing. Specific nucleotide sequences at the beginning and end of each intron signal the necessary enzymes to remove the introns from the mRNA and degrade them. The remaining sequences, which contain only exons that code for peptides and proteins, are joined together by ligation to form a mature mRNA molecule. The mature mRNA is then transported out of the nucleus and to the ribosomes, where translation takes place. Translation Translation is the cellular process by which RNA transcripts are turned into proteins and peptides, the structural and functional molecules of the cell (Fig. 2–15). Like DNA and RNA, proteins have a direction, reading their sequences left to right from the amino (NH2-) terminal to the carboxy (-COOH) terminal. Peptides are composed of amino acids (aa) joined to make a linear chain. Peptides consist of one strand of amino acids, and polypeptides (proteins) consist of more than one strand. Many peptide strands have only primary and secondary structure. Proteins can also have more complicated tertiary and quaternary structure. The making of the peptide chain(s) in the correct sequence is complicated and requires multiple steps and many molecules to carry it out. Translation takes place on the rough endoplasmic reticulum (ER) in the cytoplasm. Also called the rough ER, it is the site of the ribosomes, which are organelles composed of proteins and ribosomal RNA (rRNA). In eukaryotic organisms, translation is monocistronic in that only one ribosome reads the mRNA transcript at any time as compared to polycistronic mRNA, which has coding regions representing more than one gene and is read differently.

Figure 2–15. Translation of RNA into protein. (Lewin B: Genes VIII. Prentice Hall/Pearson Education, New York, 2004, p 122. Reprinted with permission of the author.)

Translation is a complicated process and involves three major steps: initiation, elongation, and termination. The first event of the initiation sequence is the attachment of a free methionine to a transfer RNA molecule called tRNAmet, which requires the presence of a high-energy molecule called guanine triphosphate (GTP) and a special protein called initiation factor IF2. When GTP, IF2, and factors IF1 and IF3 are present at the ribosome, tRNAmet is able to bind the small 40S subunit of the ribosome to form an initiation complex. The larger subunit of the ribosome, the 60S, also binds to the complex and hydrolyzes the GTP, and then the IFs are released. Translation is illustrated in Figures 2–16 and 2–17. There are two sites present on the 60S ribosome unit— the A site and the P site. During translation, the charged tRNAmet must occupy the P site, and the A site next to the P site must have a charged tRNA with its correct matching amino acid in position. Peptide bond formation occurs by transferring the polypeptide attached to the tRNA in the P site to the aminoacyl-tRNA in the A site. All tRNA molecules are long, single-stranded RNAs with a similar secondary structure with intramolecular hydrogen bonding. They are often described as having a cloverleafshaped conformation no matter which aa they are carrying to the translation machinery. There are two major functional areas of the tRNA molecule. The first is the anticodon; it consists of three nucleotides that hydrogen-bond to the corresponding correct site codon on the mRNA. It is this

2682_Ch02_026-044 22/05/12 11:38 AM Page 41

Chapter 2 Basic Genetics

Peptide bond synthesis involves transfer of polypeptide to aa-tRNA

Figure 2–16. Peptide bond synthesis in translation. (Lewin B: Genes VIII. Prentice Hall/Pearson Education, New York, 2004, p 137. Reprinted with permission of the author.)

hydrogen bonding that makes sure the correct aa is joined in the peptide chain by allowing only the correct tRNA molecule with the right anticodon to bond to the correct mRNA codon. The second part of the tRNA molecule is at the 3′ hydroxyl end and binds an amino acid. Only one aa can bind to one tRNA molecule; specificity is determined by the 3′ hydroxyl end. According to the recognition region, an aminoacyl synthase enzyme adds the specific aa to the correct tRNA molecule. Only when the tRNA is charged

Protein synthesis has 3 stages Initiation 40s subunit on mRNA binding site is joined by 60s subunit, and aminoacyl tRNA binds next

41

with an amino acid can it transport it to the ribosome for translation. During the elongation step of translation, the incoming tRNA binds to the A site in presence of the elongation factor called E2F. Again, GTP is hydrolyzed as the energy source to move the tRNA in the A site to the P site. As the tRNA in the A site is moved to the P site, the tRNA in the P site is released back to the cytoplasm to pick up another amino acid. In this way, tRNA molecules are conserved. The ribosomes move down the codons on the mRNA one at a time, adding a correct amino acid to the growing peptide chain. As the ribosome moves down the mRNA, it eventually comes to one of the three stop codons—UAA, UGA, or UAG—and translation of that mRNA is finished. Termination factors help the ribosome units to separate, and the peptide chain is further processed. Post-translational processing can consist of glycosylation, the addition of sugar groups, or the removal of leader peptide sequences that are used to traffic proteins to the cell membrane. Processing can also consist of complicated folding schemes that ensure the protein is in its correct tertiary form, such as the formation of disulfide bonds via cysteine aa residues. A large family of proteins called heat-shock proteins assists new proteins to be folded correctly by binding to hydrophobic (water-avoiding) sections of the nascent protein chain. Hydrogen bonding, van der Waals forces, and hydrophilic (water-attracting) regions of proteins also help to give the new protein its correct three-dimensional conformation. After translation is complete, the mRNA is rapidly degraded by enzymes (a process that helps to control gene expression) or attaches to another ribosome, and the entire translation process starts all over again. See Figure 2–18.

tRNA is an adaptor Amino acid linked to 3’ end of tRNA

Arm consists of: Base-paired stem

Singlestranded loop Anticodoncodon pairing

Figure 2–17. Stages of protein synthesis in translation. (Lewin B: Genes VIII. Prentice Hall/Pearson Education, New York, 2004, p 137. Reprinted with permission of the author.)

Figure 2–18 Schematic illustration of tRNA molecule and base pairing. (Lewin B: Genes VIII. Prentice Hall/Pearson Education, New York, 2004, p 115. Reprinted with permission of the author.)

2682_Ch02_026-044 22/05/12 11:38 AM Page 42

42

PART I

Fundamental Concepts

Common Steps in Modern Genetics Techniques Over the past three decades, the knowledge of genetics has advanced exponentially. Understanding the biochemical and biophysical nature of DNA, RNA, and peptides and proteins has allowed techniques to be developed to study these important molecules in great detail and to define the ways in which they interact in cells, groups of cells, complex multicellular organisms, and even in an entire human being. Most of the techniques used in molecular biology (the science of studying and manipulating genetic material) are based on the biochemical and biophysical properties of genes and chromosomes. The following steps are common to most techniques used in molecular biology: 1. Any material that is to be studied must first be isolated intact without structural damage. This is often done with chemicals that interact with one part of the cellular material and not another. The methods to do this can be based on pH changes, salt gradients, detergent lysis, and enzyme activation.

2. There must be a way to visualize and locate the molecular species to be studied. This is often done with probes that act as signals or beacons that will bind specifically to the molecule being analyzed; for example, DNA, by interaction with parts of the molecule, such as hybridization with the hydrogen bonds of DNA. The probes can be synthesized with radiolabels, chemiluminescence molecules, fluorochromes, or nanoparticles. 3. A method to separate out different species and subspecies being studied, such as different sequences of DNA, must be available. An example of this involves running nucleic acids through gels, binding them to columns, hybridizing them to membranes, or binding them to other molecules. 4. A method to quantify the isolated and studied species has to be used to get differences in amount as exact as possible in the process studied. Changes in optical density when exposed to UV radiation, radioisotope emission levels, fluorescence energy detection, chemiluminescence emission that can be detected with optical imaging instruments can all be used to obtain data. Several techniques used in molecular biology are reviewed in Chapter 4.

SUMMARY CHART

 

Genetics is defined as the study of inheritance or the transmission of characteristics from parents to offspring. It is based on the biochemical structure of chromatin, which includes nucleic acids and the structural proteins that constitute the genetic material as well as various enzymes that assist in genetic processes such as replication. All living organisms have specific numbers of chromosomes. Humans have 22 pairs of autosomes and one set of sex chromosomes, females (XX) and males (XY), giving a total of 46 chromosomes in diploid cells. Mendel’s law of independent assortment states that factors for different characteristics are inherited independent of each other if they reside on different chromosomes. Human chromosomes are composed of the genetic material chromatin, a complex of the nucleic acid polymer DNA wrapped around highly basic proteins called histones. The helical structure of DNA allows a lot of information to be packaged in a very small amount of space. Replication of DNA is semiconservative and is accomplished via the enzyme DNA polymerase, which produces a complementary duplicate strand of nucleic acid. Therefore, each strand of DNA can act as a template to be copied to make the opposite strand. DNA has a direction and is always read and written in the 5′ (left) to 3′ (right) direction unless specified differently for certain applications. Mutation refers to any structural alteration of DNA in an organism (mutant) that is caused by a physical or chemical agent (mutagen). Mutations can be beneficial or deleterious. Some mutations are lethal and therefore

cannot be passed on to another generation. Some mutations are silent and have no consequence on the organism in which they occur and therefore have no selective pressure against them in the population. Transcription is an enzymatic process whereby genetic information in a DNA strand is copied into an mRNA complementary strand. Eukaryotic mRNA is modified after it is made by various processing steps, such as the removal of introns and addition of a poly-A tail to the 3′ end. These processing steps take place in the nucleus of the cell before the mRNA is exported to the cytoplasmic ribosomes for translation. Translation is the complex process by which mRNA, which contains a mobile version of the DNA template encoding the genes for an organism, is turned into proteins, which are the functional units of an organism and the cells that it consists of. Translation occurs on the ribosomes, and additional steps may be necessary to get a specific protein into its final correct form, such as proteins that require disulfide linkages and proteins that are positioned within the cell membrane. Proteins are made of strings of amino acids and are always read in an amino terminal (left) to carboxyl terminal (right) direction. The polymerase chain reaction (PCR) is an in vitro method for enzymatic synthesis and amplification of specific DNA sequences using a pair of primers, usually short nucleotide sequences, that hybridize to opposite DNA strands and flank the region of interest. Various modifications have made the PCR reaction more efficient and specific and allow more complex analysis.

2682_Ch02_026-044 22/05/12 11:38 AM Page 43

Chapter 2 Basic Genetics

Review Questions 1. Which of the following statements best describes mitosis? a. Genetic material is quadruplicated, equally divided

between four daughter cells

9. Transcription can be defined as: a. b. c. d.

b. Genetic material is duplicated, equally divided

between two daughter cells c. Genetic material is triplicated, equally divided

between three daughter cells d. Genetic material is halved, doubled, then equally divided between two daughter cells 2. When a recessive trait is expressed, it means that: a. b. c. d.

One gene carrying the trait was present. Two genes carrying the trait were present. No gene carrying the trait was present. The trait is present but difficult to observe.

3. In a pedigree, the “index case” is another name for: a. b. c. d.

Stillbirth. Consanguineous mating. Propositus. Monozygotic twins.

4. Which of the following nitrogenous bases make up DNA? a. b. c. d.

Adenine, leucine, guanine, thymine Alanine, cytosine, guanine, purine Isoleucine, lysine, uracil, leucine Adenine, cytosine, guanine, thymine

5. Proteins and peptides are composed of: a. b. c. d.

Golgi bodies grouped together. Paired nitrogenous bases. Nuclear basic particles. Linear arrangements of amino acids.

6. Which phenotype(s) could not result from the mating

of a Jk(a+b+) female and a Jk(a-b+) male? a. Jk(a+b–) b. Jk(a+b+) c. Jk(a–b+) d. Jk(a–b-) 7. Exon refers to: a. b. c. d.

The part of a gene that contains nonsense mutations. The coding region of a gene. The noncoding region of a gene. The enzymes used to cut DNA into fragments.

8. PCR technology can be used to: a. b. c. d.

Amplify small amounts of DNA. Isolate intact nuclear RNA. Digest genomic DNA into small fragments. Repair broken pieces of DNA.

43

Introduction of DNA into cultured cells. Reading of mRNA by the ribosome. Synthesis of RNA using DNA as a template. Removal of external sequences to form a mature RNA molecule.

10. When a male possesses a phenotypic trait that he passes

to all his daughters and none of his sons, the trait is said to be: a. X-linked dominant. b. X-linked recessive. c. Autosomal dominant. d. Autosomal recessive. 11. When a female possesses a phenotypic trait that she

passes to all of her sons and none of her daughters, the trait is said to be: a. X-linked dominant. b. X-linked recessive. c. Autosomal dominant. d. Autosomal recessive. 12. DNA is replicated: a. b. c. d.

Semiconservatively from DNA. In a random manner from RNA. By copying protein sequences from RNA. By first copying RNA from protein.

13. RNA is processed: a. b. c. d.

After RNA is copied from DNA template. After protein folding and unfolding on the ribosome. Before DNA is copied from DNA template. After RNA is copied from protein on ribosomes.

14. Translation of proteins from RNA takes place: a. b. c. d.

On the ribosomes in the cytoplasm of the cell. On the nuclear membrane. Usually while attached to nuclear pores. Inside the nucleolus of the cell.

15. Meiosis is necessary to: a. Keep the N number of the cell consistent within

populations. b. Prepare RNA for transcription. c. Generate new DNA sequences in daughter cells. d. Stabilize proteins being translated on the ribosome.

References 1. Watson, JD, and Crick, FHC: Molecular structure of nucleic acids: A structure for deoxyribose nucleic acid. Nature 171:737, 1953. 2. Garrett, RH, and Grisham, CM: Structure of nucleic acids. In Garret, RH, and Grisham, CM: Biochemistry, 4th ed. Brooks/Cole, Cengage Learning, Boston, 2010, pp 316–353.

2682_Ch02_026-044 22/05/12 11:38 AM Page 44

44

PART I

Fundamental Concepts

3. Knippers, R, and Ruff, J: The initiation of eukaryotic DNA replication. In DNA Replication and the Cell Cycle. Springer-Verlag, New York, 1992, pp 2–10. 4. Antonarakis, SE, and Cooper, DN: Human gene mutation: mechanisms and consequences. In Speicher, MR, Antonarakis, SE, Motulsky, AG (eds): Vogel and Motulsky’s Human Genetics: Problems and Approaches, 4th ed. Springer-Verlag, Berlin Heidelberg, 2010, pp 319–351. 5. Caskey, CT, et al: Triplet repeat mutations in human disease. Science 256:784–789, 1992. 6. Yamamoto, F, et al: Molecular genetic basis of the histo-blood group ABO system. Nature 345:229, 1990. 7. Le Van Kim, C, et al: Molecular cloning and primary structure of the human blood group RhD polypeptide. Proc Natl Acad Sci USA 89(22):10929, 1992.

Bibliography Alberts, B, et al: Molecular Biology of the Cell, 4th ed. Garland Science, New York, 2002. Calladine, CR, Drew, HR, Luise, BF, and Travers, AA: Understanding DNA, the Molecule and How it Works, 3rd ed. Elsevier, San Diego, CA, 2004.

Clark, DP, and Russell, LD: Molecular Biology Made Simple and Fun, 2nd ed. Cache River Press, St. Louis, MO, 2000. Glick, BR, Pasternak, JJ, and Patten, CL: Molecular Biotechnology: Principles and Applications of Recombinant DNA, 4th ed. ASM Press, Washington, DC, 2009. Harmening, DM: Modern Blood Banking and Transfusion Practices, 5th ed. FA Davis, Philadelphia, PA, 2005. Hillyer, CD, Silberstein, LE, Ness, PM, Anderson, KC, and Roback, J: Blood Banking and Transfusion Medicine, Basic Principles and Practice. Churchill Livingstone, Philadelphia, PA, 2007. Lewin, B: Genes VIII. Prentice Hall, New York, 2003. Quinley, ED: Immunohematology: Principles and Practice, 3rd ed. Lippincott Williams & Wilkins, Philadelphia, PA, 2010. Roback, J, Combs, M, Grossman, B, and Hillyer, C: Blood Group Genetics: Technical Manual, 16th ed. American Association of Blood Banks, Bethesda, MD, 2009. Roback, J, Combs, M, Grossman, B, and Hillyer, C: Molecular Biology and Immunology in Transfusion Medicine: Technical Manual, 16th ed. American Association of Blood Banks Bethesda, MD, 2009. Trent, RJ: Molecular Medicine, 3rd ed. Elsevier Academic Press, Burlington, MA, 2005.

2682_Ch03_045-076 28/05/12 2:32 PM Page 45

Chapter

3

Fundamentals of Immunology Lorraine Caruccio, PhD, MT(ASCP)SBB, and Scott Wise, MHA, MLS(ASCP)SBB

Introduction Overview of the Immune System Cellular and Humoral Immunity Innate and Acquired Immunity Cells and Organs of the Immune System B Cells T Cells Antigen-Presenting Cells Immune System Organs Immune Maturation Cell Lineages and Markers Cytokines and Immunoregulatory Molecules Immune System Genetics Characteristics of Immunoglobulins Immunoglobulin Structure Immunoglobulins Significant for Blood Banking Immunoglobulin Variations Immunoglobulin FC Receptors Complement System Classical Complement Pathway Alternative Complement Pathway Lectin Complement Pathway Membrane Attack Complex

Binding of Complement by RBC Antibodies Characteristics of Antigens Characteristics of Blood Group Antibodies Polyclonal and Monoclonal Antibodies Naturally Occurring and Immune Antibodies Unexpected Antibodies Alloantibodies and Autoantibodies Characteristics of Antigen-Antibody Reactions Intermolecular Binding Forces Antibody Properties Host Factors Tolerance Detection of RBC Antigen-Antibody Reactions Blood Samples Required for Testing Traditional Laboratory Testing Methods Factors That Influence Agglutination Reactions Centrifugation Antigen-Antibody Ratio Effect of pH Temperature Immunoglobulin Type Enhancement Media

Protein Media Low Ionic Strength Solution Media Polyethylene Glycol and Polybrene Proteolytic Enzymes Antihuman Globulin Reagents Chemical Reduction of IgG and IgM Molecules Monoclonal Versus Polyclonal Reagents Nontraditional Laboratory Methods Flow Cytometry Diseases Important in Blood Bank Serologic Testing Immunodeficiency Hypersensitivity Monoclonal and Polyclonal Gammopathies Autoimmune Disease Hemolytic Disease of the Newborn Blood Product Transfusions and the Immune System Summary Chart Review Questions References

OBJECTIVES 1. Outline the different components of the immune system and identify their functions. 2. Describe the characteristics of the major cells of the immune system and their functions. 3. List the major effector molecules and the roles they play in the immune response. 4. Outline the basic steps of hematopoiesis in the immune system. 5. Explain the function of the major histocompatibility complex (MHC) class I and II molecules. 6. Describe the physical characteristics of immunoglobulins in relation to structure and list the different subtypes. 7. Explain the activation sequences of the three major complement pathways and describe how they come to a common starting point. 8. List the methods used in the blood bank to detect antibodies and complement bound to red blood cells. 9. Describe the immune response, including antigen-antibody reactions, lymphocyte functions, and host factors that can activate and suppress the immune system. Continued 45

2682_Ch03_045-076 28/05/12 2:32 PM Page 46

46

PART I

Fundamental Concepts

OBJECTIVES—cont’d 10. List the traditional laboratory techniques used in blood bank testing. 11. Identify the various factors that affect agglutination reactions. 12. Describe some of the common diseases that can affect blood bank testing.

Introduction The immune system (IS) is complicated, tightly controlled, and includes tissues, organs, cells, and biological mediators that coordinate to defend a host organism against intrusion by a foreign substance or abnormal cells of self-origin. Immunity refers to the process by which a host organism protects itself from attacks by external and internal agents. Immunity also confers protection from nonself and abnormal self-elements, which are controlled at different levels. The number of different types of nonself organisms includes unicellular and multicellular organisms, such as viroids, viruses, bacteria, mycoplasma, fungi, and parasites. Tumor cells, which are too old or misshapen to function, and cells destined for termination within the host must be recognized and eliminated. The response and elimination of organisms and unwanted cells is accomplished through cellular and/or humoral mechanisms. The cellular defense mechanism is mediated by various cells of the IS, such as macrophages, T cells, and dendritic cells, which function to eliminate viruses, bacteria, cancer cells, and other cellular pathogens. In the humoral mechanism, specific antibodies and complement components are produced in plasma, saliva, and other bodily secretions. These antibodies bind to specific receptor sites on cells. Complement may also bind to immunoglobulin molecules that have specific complement receptor sites. The extent of activation and the amount of damage that occurs to red blood cells is dependent upon the complement pathway involved and on several other host factors. Immunoglobulins, or antibodies, have special significance for transfusion medicine, because antigens present on transfused cells may cause reactions in the recipient and complicate therapy. The majority of blood bank testing is focused on the prevention, detection, and identification of blood group antibodies and on the typing of RBC antigens. Antigen characteristics, as well as host factors, have an impact on the immune response. Knowledge of these characteristics enables testing problems to be resolved. Understanding the IS and its responses is essential to understanding the factors that can affect agglutination reactions between RBCs and antibodies and various testing modifications. Detection of alloantibodies or autoantibodies in routine blood bank testing procedures is of the utmost importance in providing compatible blood to patients. This detection is dependent upon several factors, including binding forces between antigens and antibodies, properties of the antibody itself, and individual host characteristics. Antigen-antibody reactions are influenced by a number of factors, including distance, antigen-antibody ratio, pH, temperature, and immunoglobulin type (Box 3–1).

BOX 3–1

Factors Affecting Antigen-Antibody Reactions • • • • •

Distance Antigen-antibody ratio pH Temperature Immunoglobulin type

Both traditional and nontraditional laboratory testing methods are currently utilized in the transfusion service. These methods focus on either the detection of antigens or on the detection of antibodies. This chapter provides an introduction to the many areas of immunology and how they impact transfusion medicine. It will include a brief introduction to the biology and biochemistry of the immune system, and the application of testing procedures used in evaluating the immune response as related to blood transfusion. A brief description of immune-mediated diseases important to transfusion medicine is included at the end of the chapter.

Overview of the Immune System Basic Concepts All organisms at all levels of life are challenged constantly by various factors from their environment and must protect against them. The host organism is a rich source of nutrients and protection for an organism that is able to avoid the host’s IS. One of the most fundamental concepts in immunology is the idea of self versus nonself and how the IS distinguishes between the two. The two terms have now been broadened in meaning. Self refers to anything that is derived from the host genome and the rearrangement of host genes. It includes cells, fluids, molecules, and more complex structures of a host organism. Anything put into the host body, even a close genetic match, can be regarded as nonself and therefore can be rejected by a response of the IS. Nonself refers to anything physically outside the host, whether a living organism (parasites, fungus) or nonliving toxin (poison ivy fluid, insect venom). When foreign objects or damaged host cells are detected by the IS, an immune response occurs. Immune responses occur at different levels and are either primary (natural, innate) or secondary (adaptive, acquired). The overall mechanisms and components of each are outlined in Table 3–1 and Table 3–2. The innate immune response consists of physical barriers, biochemical effectors, and immune cells. The first step of

2682_Ch03_045-076 28/05/12 2:32 PM Page 47

Chapter 3 Fundamentals of Immunology

Table 3–1 Comparison of the Major Mechanisms of the Immune System INNATE OR NATURAL IMMUNITY

ACQUIRED OR ADAPTIVE IMMUNITY

• Primary lines of defense

• Supplements protection provided by innate immunity

• Early evolutionary development

• Later evolutionary development—seen only in vertebrates

• Nonspecific

• Specific

• Natural—present at birth

• Specialized

• Immediately available

• Acquired by contact with a specific foreign substance

• May be physical, biochemical, mechanical, or a combination of defense mechanisms

• Initial contact with foreign substance triggers synthesis of specialized antibody proteins resulting in reactivity to that particular foreign substance

• Mechanism does not alter on repeated exposure to any specific antigen

• Memory

• Response improves with each successive encounter with the same pathogen • Remembers the infectious agent and can prevent it from causing disease later • Immunity to withstand and resist subsequent exposure to the same foreign substance is acquired

innate defense is external, including skin and enzymes present on the skin’s surface. The second line of innate defense is internal and can recognize common invaders with a nonspecific response, such as phagocytosis that does not have to be primed. The last line of defense is the acquired immune response that needs time and reorganization to mount an effective and specific reaction and that protects against a repeat attack by the same organism using immune memory. The IS’s specificity also prevents the host from becoming attacked and damaged during an immune response. The localized nature of an immune reaction also prevents systemic damage throughout the host organism. The wide variety of potential organisms and substances that can invade the host requires a vast array of means to recognize and remove them. The acquired immune response must be capable of generating a near-infinite level of specific responses to all the different complex organisms and substances that the host can encounter over its lifetime.

47

Cellular and Humoral Immunity The two major components of the vertebrate IS are cellular and humoral immunity. Cellular immunity is mediated by various IS cells, such as macrophages, T cells, and dendritic cells. Lymphokines are other effector molecules that play critical roles in the cellular system by activating and deactivating different cells, which allows cells to communicate throughout the host body. Lymphokines are powerful molecules that include cytokines and chemokines. Humoral immunity consists of the fluid parts of the IS, such as antibodies and complement components found in plasma, saliva, and other secretions. One of the most important parts of humoral immunity is the antibody. Antibodies are also called immunoglobulins—immune because of their function, and globulin because they are a type of globular soluble protein. They are found in the gamma globulin portion of plasma or serum when it is separated by fractionation or electrophoresis. The function of the antibody is to bind to foreign molecules called antigens. Most antigens are found on the surface of foreign cells or on damaged internal cells. A key feature of antigen-antibody reactions is their specificity. Only one antibody reacts with one antigen, or one part (an epitope or antigenic determinant) of a complex antigen. An immune reaction against an antigen stimulates the production of antibodies that will match the epitope of the antigen. The binding reaction of antigen and antibody has often been called a lock and key mechanism, referring to its specific conformation. Antigenantibody complex formation inactivates the antigen and elicits a number of complicated effector mechanisms that will ultimately result in the destruction of the antigen and the cell to which it is bound. The laboratory study of antigen-antibody reactions is called serology and has been the basis of blood bank technology for many years. Antibody screening methods such as the indirect antibody test and crossmatching techniques rely on the detection of antigen-antibody complexes by screening for antibodies in the plasma or sera. The direct antiglobulin (Coombs) test relies on the detection of antibodies (and complement) bound to the surface of RBCs.

Innate and Acquired Immunity One of the ways to characterize the immune system is by its cellular and humoral components. Another way is by the two major parts of the IS, which work to prevent infection and damaged cells from destroying the host; namely, innate and acquired immunity. The innate part of the system is less complicated and more primitive and does not function in a specific way; rather, it recognizes certain complex repeating patterns present on common invading organisms. The innate part can function immediately to stop host organisms from being infected. The acquired immune response is more advanced and was developed after vertebrates had evolved. It relies on the formation of specific antigen-antibody complexes and specific cellular responses. Acquired immunity allows for a specific

2682_Ch03_045-076 28/05/12 2:32 PM Page 48

48

PART I

Fundamental Concepts

Table 3–2 Cellular and Humoral Components of the Immune System INNATE OR NATURAL IMMUNITY

ACQUIRED OR ADAPTIVE IMMUNITY

First Line of Defense

Second Line of Defense

Third Line of Defense

Internal Components

Internal Components

Internal Components

PHYSICAL

CELLULAR

CELLULAR

• Intact skin

• Phagocytic cells

• Lymphocytes

• Mucous membranes

• Macrophages-Dendritic cells

• T cells

• Cilia

• Monocytes

• TH

• Cough reflex

• PMNs: Large granular leukocytes

• TC

BIOCHEMICAL

• NK cells

• T memory cells

• Secretions

HUMORAL (FLUID)/BIOCHEMICAL

• B cells

• Sweat

• Complement-alternate pathway

• B memory cells

• Tears

• Cytokines

• Plasma cells

• Saliva

• Interferons

HUMORAL

• Mucus

• Interleukins

• Antibodies

• Very low pH of vagina and stomach

• Acute inflammatory reaction

• Complement-classic pathway • Cytokines

response, and IS memory allows resistance to a pathogen that was previously encountered. Innate immunity is the immediate line of immune defense. There are two important features of innate immunity. First, the innate immune system is nonspecific. The same response is used against invading organisms, no matter what the source is, as long as the innate IS can recognize them as nonself. Innate immunity is present at birth and does not have to be learned or acquired. Second, it does not need modifications to function and is not altered with repeated exposure to the same antigen. Because innate immunity functions so well as a first line of defense, it was maintained in the IS of vertebrates during evolution. Physical and biochemical barriers and various cells make up the innate IS. Physical barriers include intact skin, mucous membranes, cilia lining the mucous membranes, and cough reflexes. Biochemical barriers of the innate system include bactericidal enzymes such as lysozyme and RNases, fatty acids, sweat, digestive enzymes in saliva, stomach acid, and low pH. Innate immune cells include phagocytic leukocytes and natural killer (NK) cells. Phagocytic cells of different types are found in most tissues and organs of individuals, including the brain, liver, intestines, lungs, and kidneys. Phagocytes include circulating monocytes in the blood and peripheral macrophages (activated monocytes) that can move between vessel walls. Phagocytes recognize complex molecular structures on the surface of invading cells or in the secretions and fluids of the host body. They remove the

invading organisms by engulfing and digesting them with vesicle enzymes. Two major cells that can use phagocytosis to remove pathogens are the polymorphonuclear cells (which include neutrophils, basophils, and eosinophils) and the mononuclear cells (which include the monocytes in plasma and the macrophages in tissues). Various molecules of the IS collaborate with the innate IS’s cells. Opsonins are factors that include antibodies and complement components in plasma that coat pathogens and facilitate phagocytosis. When phagocytes ingest foreign cells and destroy them, they can become activated to release soluble polypeptide substances called cytokines that have various effects on other cells of the immune and vascular systems (Table 3–3 lists important cytokines). There are a large number of different cytokines; some have unique functions and others have overlapping functions. Some work together, and some oppose the functions of other cytokines. Many are secreted, and some are membrane receptors. Cytokines help to regulate the immune response in terms of specificity, intensity, and duration. Another important component of the innate immune system is the complement system. Complement has three major roles in immunity: (1) the final lysis of abnormal and pathogenic cells via the binding of antibody, (2) opsonization and phagocytosis, and (3) mediation of inflammation. The proteins of the complement system are enzymes that are normally found in the plasma in a proenzyme inactive state. Three ways the complement proteins can be activated are the

2682_Ch03_045-076 28/05/12 2:32 PM Page 49

Chapter 3 Fundamentals of Immunology

49

Table 3–3 Cytokines and Their Functions CYTOKINE

SOURCE

STIMULATORY FUNCTION Interleukins

IL-1

Mf, fibroblasts

Proliferation-activated B cells and T cells

IL-2

Induction PGE2 and cytokines by Mf

IL-3

Induction neutrophil and T-cell adhesion molecules on endothelial cells

IL-4

Induction IL-6, IFN-b1, and GM-CSF

IL-5

Induction fever, acute phase proteins, bone resorption by osteoclasts

IL-6

T

Growth-activated T cells and B cells; activation NK cells

IL-7

T, MC

Growth and differentiation hematopoietic precursors

IL-8 IL-9

Mast cell growth CD4, T, MC, BM stroma

Proliferation-activated B cells, T cells, mast cells, and hematopoietic precursor

IL-10

Induction MHC class II and FC on B cells, p75 IL-2R on T cells

IL-11

Isotype switch to IgG1 and IgE

IL-12

Mf APC and cytotoxic function, Mf fusion (migration inhibition)

IL-13

CD4, T, MC

Proliferation-activated B cells; production IgM and IgA Proliferation eosinophils; expression p55 IL-2R

CD4, T, Mf, MC, fibroblasts

Growth and differentiation B-cell and T-cell effectors and hemopoietic precursors Induction acute phase proteins

BM stromal cells

Proliferation pre-B cells, CD4 cells, CD8 cells, and activated mature T cells

Monocytes

Chemotaxis and activation neutrophils Chemotaxis T cells Inhibits IFN-g secretion

T

Growth and proliferation T cells

CD4, T, B, Mf

Inhibits mononuclear cell inflammation

BM stromal cells

Induction acute phase proteins

T

Activates NK cells

T

Inhibits mononuclear phagocyte inflammation Colony-Stimulating Factors

GM-CSF

T, Mf, fibroblasts, MC, endothelium

Growth of granulocyte and Mf colonies

G-CSF

Fibroblasts, endothelium

Activated Mf, neutrophils, eosinophils

M-CSF

Fibroblasts, endothelium, epithelium

Growth of mature granulocytes Growth of macrophage colonies

Steel factor

BM stromal cells

Stem cell division (c-kit ligand) Tumor Necrosis Factors

TNF-a

Mf, T

TNF-b

T Continued

2682_Ch03_045-076 28/05/12 2:32 PM Page 50

50

PART I

Fundamental Concepts

Table 3–3 Cytokines and Their Functions—cont’d CYTOKINE

SOURCE

STIMULATORY FUNCTION Interferons

IFN-a

Leukocytes

IFN-b

Fibroblasts

IFN-g

T

Antiviral; expression MHC I

Other TGF-b

T, B

LIF

T

Adapted from Delves, PJ, Martin, SJ, Burton, DR, Roitt, IM: Roitt’s Essential Immunology, 8th ed. Wiley-Blackwell, Malden, 2011. APC = antigen-presenting cells; BM = bone marrow; CSIF = cytokine synthesis inhibitory factor, Fc = immunoglobulin Fc receptor for IgE; G-CSF = granulocyte colony-stimulating factor; GM-CSF = granulocyte monocyte/macrophage colony-stimulating factor; IFN = interferon; IL = interleukin; LIF = leukocyte inhibitory factor; MC = mast cell; M-CSF = monocyte colonystimulating factor; MHC = major histocompatibility complex; Mf = macrophage; NK = natural killer cells; PGE2 = prostaglandin E2; T = T lymphocyte; TGF = transforming growth factor; TNF = tumor necrosis factor.

classic, alternative, and lectin pathways; all have essentially the final result of cell lysis and inflammation. The classic pathway uses antigen-antibody binding and therefore is a specific activator of complement. The alternative pathway activates complement by recognizing polysaccharides and liposaccharides found on the surfaces of bacteria and tumor cells; therefore, it uses nonspecific methods of activation. The lectin pathway is activated by mannose binding proteins bound to macrophages. Inflammation is also a critical component of the innate IS and is familiar to most people when they have a minor wound that has redness and warmth at the abrasion site. Inflammation is initiated by any type of tissue damage, whether it be to the skin or to an internal organ. Burns, infections, fractures, necrosis, and superficial wounds all elicit an inflammatory response that is characterized by an increase in blood flow to the wounded area, increased blood vessel permeability at the site to allow for greater flow of cells, a mobilization of phagocytic cells into the site, and a possible activation of acute phase and stress response proteins at the site of tissue damage. Eventually the wound is repaired, new tissue grows in place of the damaged tissue, and inflammation is stopped. Uncontrolled inflammation can result in unwanted damage to healthy tissues. The regulation of inflammation is tightly controlled and requires signals to effectively turn it on and off. Acquired immunity is the other major arm of the host’s IS and is the most highly evolved. It is also the most specific and allows the IS to have memory of pathogens it has encountered previously. The acquired system is present only in vertebrates. The term acquired refers to the fact that the immunity is acquired via specific contact with a pathogen or aberrant cell. The term adaptive refers to the ability to adapt to and destroy new complex pathogens, although it must first react to them through complex recognition processes. Acquired immunity is specific in recognition of new

pathogens and has specific responses, depending on the type of pathogen it encounters. The acquired IS uses antibodies as specific immune effectors. Antigen specificity and uniqueness determine the particular antibody that will bind to it. The antigenantibody complex is a three-dimensional interaction that does not allow recognition of near misses. For example, antibodies against one blood group antigen do not react against another blood group antigen. An antigen that an antibody is made against is sometimes referred to as its antithetical antigen. The fact that acquired immunity has memory means medical histories of patients that require transfusions are absolutely critical. Antibodies do not always remain in plasma at levels observable with serologic testing, and if antigen-positive RBC units are transfused in a sensitized patient, the second antibody response against the transfused cell antigens can be more vigorous, resulting in intravascular RBC hemolysis.

Cells and Organs of the Immune System The different types of immune system cells can be distinguished by the membrane markers they possess. These are referred to as clusters of differentiation (CD) markers and are detected by immunotyping methods. The immunization process requires many different types of cells and tissues, including phagocytic granulocytes of the innate system and monocytes and macrophages. Lymphocytes are also important in acquired immunity. They are divided into two major types, the T lymphocyte (T cell) and the B lymphocyte (B cell). The T lymphocyte matures in the thymus gland and is responsible for making cytokines and destroying virally infected host cells. B lymphocytes mature in the bone marrow, and when stimulated by an antigen, evolve into plasma cells that secrete antibody. Natural killer cells are a type of lymphocyte that plays a role

2682_Ch03_045-076 28/05/12 2:32 PM Page 51

Chapter 3 Fundamentals of Immunology

in immune protection against viruses. Dendritic cells are present throughout many systems of the body and are responsible for antigen processing. Macrophages can also process antigens. T and B cells communicate with each other and are both necessary for antibody production. B cells undergo gene rearrangement in order to have the correct antibody made that can react with the correct antigen. T cells also have receptors that undergo gene rearrangement. The receptors on the cell membranes of T and B lymphocytes allow them to recognize foreign substances. Lymphocytes recognize only one specific antigen, which is determined by the genetic programming of that lymphocyte. Because there are so many different antigens that pathogens can carry, the IS has adapted to recognize millions of different antigens, with a specific antibody that will match only one particular antigen. Therefore, if a foreign antigen is present, only a small percentage of the host’s antibodies and T-cell receptors will recognize it. In cases where an antigen is recognized by more than one antibody, a process of clonal selection happens, in which the different cells that recognize the different epitopes of the antigen are expanded. In transfusion medicine, this plays a role in selecting the best antibody reagents for testing, as not all epitopes of a complex antigen, including blood group antigens, will be equally reactive. The maturation of B and T cells occurs after an antigen is encountered. Both B and T cells mature into what are called effector cells, which are the functional units of the IS. The final effect that B and T cells can cause is the elimination of pathogens and foreign cells. Immune memory is also acquired when lymphocytes mature into memory cells after antigenic stimulation; this allows the IS to recognize antigens from previous encounters. Once an infection is cleared, some of the cells that can recognize the antigen remain in circulation. The lymphocytes are permanently set to respond to the same antigen again by the process of memory. The second time this antigen is encountered, memory allows for a more effective and rapid immune response. Memory cells can persist for the lifetime of the host. It is one of the reasons that some immunizations with vaccines do not have to be repeated, except on a cautionary basis to keep the immunization active.

B Cells Antibodies can be secreted or membrane-bound. Antibodies are secreted by mature B cells called plasma cells and bind to antigens in a specific manner. The antigens are usually in soluble form in the plasma. The receptor on the B cell that recognizes the antigen is a membrane-bound antibody. When the receptor antibody on the B cell reacts with a specific antigen and recognizes it, the B cell is activated to divide. The cells produced from this rapid division mature into plasma cells and memory B cells. Memory B cells have antibody on their surfaces that is of the same conformation as that of the B cell from which they were derived. Plasma cells are antibody factories that make large amounts of one specific type of antibody in a soluble form

51

that remains in circulation in the plasma, body secretions, and lymphatics. Antibodies can neutralize toxic substances and antigens that are encountered by binding to them and therefore preventing them from interacting with the host. When the antigenic site is nonreactive because of antibody binding, it cannot interact with host cells to infect them or damage them. Also, binding of antigen by antibody brings about opsonization, which aids in the direct killing of pathogens by cell lysis. When complement is activated by an antigen-antibody complex, the pathogen can be destroyed. Pathogens can be destroyed intra- or extravascularly. Antibodies are one of the most important components of the IS and blood bank testing procedures.

T Cells T cells are another very important component of the cellular part of acquired immunity. One of the major differences of cellular immunity compared to humoral immunity is that T cells recognize antigens that are internalized within a host cell. The antigens are then processed and presented on the host cell surface in small peptide fragments. T cell–mediated immunity is involved in the response against fungal and viral infections, intracellular parasites, tissue grafts, and tumors. T-cell receptors do not recognize foreign antigen on their own, as B cells do; they require help in the form of cell membrane proteins known as major histocompatibility complex (MHC) molecules. Therefore, there is a certain level of restriction placed on the acquired cellular branch of the IS, as determined by the inherited MHC molecules on host cells. The MHC genes determine the human leukocyte antigens (HLA) present on leukocytes and other cells; they have been known for many years to cause rejection of tissue grafts.

Advanced Concepts There are two major classes of MHC genes and antigens: MHC class I and MHC class II. MHC class I antigens are found on most nucleated cells in the body, and MHC class II antigens are found on most antigen presenting cells. In humans, MHC class I genes code for the HLA-A, HLA-B, and HLA-C antigens; whereas MHC class II genes code for HLA-DR, HLA-DQ, and HLA-DC antigens. MHC classes I and II are important in the recognition of foreign substances and the immune reactions against them. There are two major functions of T cells. The first major function is to produce immune mediating substances such as cytokines, which influence many immune functions throughout the body. The second major function is to kill cells that contain foreign antigen. When T cells are activated by antigen, they start to secrete cytokines and change their cellular interactions (see Table 3–3). T cells are also grouped into two major categories with two major functions: T helper (TH) cells and T cytotoxic (TC) cells. TH cells are also distinguished by the membrane marker CD4; TC cells are distinguished by the marker CD8. TH cells are further grouped into TH1 and TH2 and respond to

2682_Ch03_045-076 28/05/12 2:32 PM Page 52

52

PART I

Fundamental Concepts

different cytokines. TH cells have the ability to recognize antigen, along with MHC class II molecules, and provide help to B cells to evolve into plasma cells and make antibodies. TH cells therefore determine which antigens become IS targets, as well as which immune mechanisms will be used against them. TH cells aid in the proliferation of immune cells after they encounter antigen.

Antigen-Presenting Cells There are several types of leukocytes that function as antigenpresenting cells (APCs), including macrophages, neutrophils, and some B cells. In addition to leukocytes, there are specialized immune cells capable of antigen presentation. These include the different types of dendritic cells present in the skin (Langerhans cells), nervous tissue (glial cells), lymph nodes, spleen, intestines, liver (Kupffer cells), bone (osteoclasts), and thymus. These APCs first phagocytize the foreign antigen, process it internally, and then with the help of MHC molecules, present short peptide sequences of the antigen on their cell membranes. TH cells can then recognize the antigen in the context of MHC presentation and respond to it by the appropriate immune reaction.

Immune System Organs Basic Concepts The organs of the IS are divided into primary and secondary systems. The primary lymphoid organs are the thymus and bone marrow, where immune cells differentiate and mature. The secondary lymphoid organs include the lymph nodes and spleen, in which immune cells interact with each other and process antigens (Table 3–4).

always possible. It usually takes days to months for all the aspects of an efficient immune response to happen from the moment an antigen is first encountered. The lag phase, until an appropriate immune response occurs, is called the latency, preseroconversion, or window period. It is during this time that antibody cannot be detected with serologic testing. During the latency period, however, T and B cells are very active in processing antigen and initiating the primary response to the antigen. The first antibodies made against the new antigen are different from the antibodies of the secondary response. The primary antibodies are the immunoglobulin M (IgM) subclass, whereas the antibodies of the secondary response are the immunoglobulin G (IgG) subclass and have a different structure. Figure 3–1 depicts the primary and secondary antibody responses. After the antigen is cleared, memory cells are stored in immune organs of the host. When the same antigen is encountered again, the memory cells are activated and produce a stronger and more rapid response. IgG antibodies are formed during the secondary response and are made in great quantities, and although IgM is made during the primary response, there is a period when it overlaps with the production of IgG antibodies at the beginning of the secondary response. IgG secondary antibodies have a higher avidity for antigen and can be produced by much lower concentrations of antigen. Secondary antibodies can usually be measured within 1 to 2 days. For example, a primary antibody may require more than 100-fold excess of antigen to initiate the first response. Many of the antigens that stimulate the primary response have multiple repeating epitopes such as polysaccharides and therefore are good immune stimulators at lower concentrations.

Cell Lineages and Markers Immune Maturation Because of the complexity and diversity of immune responses, a specific immediate immune response is not

Table 3–4 Lymphoid Organs Associated with the Acquired Immune System PRIMARY LYMPHOID ORGANS

SECONDARY LYMPHOID ORGANS

• Thymus

• Lymph nodes

• Bone marrow

• Spleen • Mucosa-associated tissues

Site of maturation for T and B cells

Site of cell function for mature T and B cells

Lymphocytes differentiate from stem cells, then migrate to secondary lymphoid organs

Cells interact with each other and with accessory cells and antigens

Advanced Concepts Nearly all cells of the host’s body, especially the various leukocytes, have specific cell receptors that interact with other cells and receive signals from cellular messenger systems. Macrophages, NK cells, T and B cells, and APCs can interact directly with cell-to-cell communication or indirectly with soluble mediators through a complex system. These cell surface molecules are classified by complex in vitro testing using monoclonal antibodies. They specify cellular definitions and functions, including maturation levels and lineage specificity and are designated as CD markers. These markers on cells can change during the lifetime of the cell or in response to infection or activation. Currently, there are more than 200 different CD markers known. The first were identified on immune cells. CD markers are critical to identifying hematopoietic cell maturation stages and lineages. All immune cells originate from pluripotent hematopoietic progenitors (or CD34-positive cells) through one of two pathways of lineage, the myeloid and the lymphoid. Various growth factors are responsible for differentiating

2682_Ch03_045-076 28/05/12 2:32 PM Page 53

Antibody Concentration in Serum

Chapter 3 Fundamentals of Immunology

53

SECONDARY

PRIMARY

Total Ab Steady state IgG

Total Ab Logarithmic increase

IgG

Decline

IgM Negative phase

Inductive period

Primary immunogenic stimulation

IgM

Secondary immunogenic stimulation

IgM

IgM IgG

IgG Figure 3–1. Schematic representation of primary and secondary antibody responses. Note the enhanced antibody production and expanded antibody-producing cell population during the secondary antibody response. (From Herscowitz, HB: Immunophysiology. In Bellanti, JA [ed]: Immunology III. WB Saunders, Philadelphia, 1985, p 117, with permission.)

and maturing stem cells into the many different cells of the IS. Growth factors also allow progenitor stem cells to reproduce and differentiate. The cells of the myeloid lineage consist of phagocytic cells such as the monocytes and macrophages, often referred to as the mononuclear phagocytic system (MPS); the granulocytes or polymorphonuclear cells (PMNs), the neutrophils, eosinophils, and the basophils; and the APCs such as the dendritic cells in the skin and liver. Erythrocytes and platelets originate from this system. The lymphoid lineage consists of the various subpopulations of lymphoid cells, the T cells, B cells, and NK cells. The myeloid-monocyte precursors originate in the bone marrow and then differentiate into circulating blood monocytes. When monocytes encounter antigen, they can differentiate into tissue macrophages. Phagocytic cells process antigens for acquired immunity and can directly kill many pathogens such as bacteria and fungi as part of innate immunity. MPS cells present antigen to lymphocytes and interact with other immune cells via cell membrane receptors. The FC part of the antibody receptor and the complement receptor CR1 are used by phagocytes during opsonization.1 When these cells are functioning as APCs, they express the MHC class II molecules on their membranes and lack the FC receptor. Granulocytes originate in the bone marrow. They are the predominant leukocyte in the circulation of the mature adult (60% to 70%). Granulocytes all have granules in their cytoplasm and are of three types, distinguished by the hematologic

"Memory" cells

"Memory" cells

staining of their granules. The neutrophils stain a faint purple or neutral color (neutral granules), the eosinophils a reddish orange color (acidic granules), and the basophils a bluish black color (basic granules). The main role of these cells is phagocytosis; they function primarily in acute inflammatory responses and have enzymes that allow them to destroy engulfed pathogens. All three types of granulocytes possess receptors for the FC portion of IgG (CD16) and complement receptors C5a, CR1(CD35), and CR3(CD11b). Additionally, eosinophils possess low-affinity FC receptors for IgE and therefore play a critical role in allergic reactions and inflammation in parasitic infections. Basophils and mast cells (a type of tissue basophil) possess high-affinity FC immunoglobulin E (IgE) receptors, are powerful effectors of inflammation and allergic reactions, and can cause the release of localized histamine. Lymphocytic cells are generated in the thymus or bone marrow and travel through the circulatory system to the lymph nodes and spleen, where they mature and differentiate. In a mature adult, the lymphocytes account for about 20% to 30% of the circulating leukocytes. In primary organs, these cells acquire receptors that enable them to interact with antigens and to differentiate between self and nonself antigens, a very critical part of lymphocyte maturation and the acquired IS in general. In the secondary organs, immune cells are provided with a highly interactive environment in which immune responses are exchanged and made specific. Remember,

2682_Ch03_045-076 28/05/12 2:32 PM Page 54

54

PART I

Fundamental Concepts

there are two primary classifications of lymphocytes, T and B cells, and these similar-looking cells can be distinguished by the presence of specific cell markers by means of using sophisticated immunologic methods of testing, such as flow cytometry (discussed later in this chapter). Specific to the T cell is the T-cell receptor (TCR), which is in proximity to and usually identified with the CD3 complex on the T-cell membrane. It associates in cell-to-cell contacts and interacts with both antigenic determinants and MHC proteins. In addition to CD3 on T cells, there is the separate CD2 marker, which is involved in cell adhesion. It has the unique ability to bind with sheep erythrocytes in vitro.2 Remember that TH cells have the CD4 marker and recognize antigen together with the MHC class II molecules, and TC cells possess CD8 markers and interact with MHC class I molecules.3 The ratios of T cells with CD4 versus CD8-positive cells can be a marker for particular diseases. One of the defining features of AIDS is a reversal of the typical CD4 to CD8 ratio, which helped to explain some of the pathology of this illness. There are also compounds referred to as superantigens, which can stimulate multiple T cells, causing them to release large amounts of cytokines. Certain bacteria toxins are superantigens and can lead to lethal reactions in the host if the immune system is overstimulated. B cells are defined by the presence of immunoglobulin on their surface; however, they also possess MHC class II antigens (antigen presentation); the complement receptors CD35 and CD21; FC receptors for IgG; and CD19, CD20, and CD22 markers, which are the CD markers used to identify B cells. Membrane-bound immunoglobulin may act as an antigen receptor for binding simple structural antigens or antigens with multiple repeating determinants (referred to as T cell–independent antigens, meaning they do not require the intervention of T-cell help). When T cell–dependent antigens (structurally complex and unique substances) are encountered, B cells require the intervention of T cells to assist in the production of antibody. When B cells become activated, they mature and develop into plasma cells, which produce and secrete large quantities of soluble Ig into tissue or plasma. The third major class of lymphocytes, the NK cells, are sometimes referred to as third population cells because they originate in the bone marrow from a developmental line distinct from those of T and B lymphocytes. They are also referred to as large granular lymphocytes. Unlike B cells, NK cells do not have surface Ig or secrete Ig, nor do they have antigen receptors like the TCR of T cells. NK cells have the CD56 and CD16 markers and do not require the presence of an MHC marker to respond to an antigen. They are thymus-independent and are able to lyse virally infected cells and tumor cells directly in a process known as antibody-dependent cellmediated cytotoxicity (ADCC) by anchoring immunoglobulin to the cell surface membrane through an FC receptor.

Cytokines and Immunoregulatory Molecules Cytokines are soluble protein or peptide molecules that function as powerful mediators of the immune response.

There are two main cytokine types: lymphokines, which are produced by lymphocytes, and monokines, which are produced by monocytes and macrophages. Cytokines function in a complex manner by regulating growth, mobility, and differentiation of leukocytes. One cytokine may act by itself or together with other cytokines. Other cytokines oppose the actions of one or more cytokines and function to quantitatively increase or decrease a particular immune reaction. Some cytokines are synergistic and need each other to have their full effect. The effects of cytokines can be in the immediate area of their release, or they can travel through the plasma to affect distant cells and tissues. There is often significant overlap in how cytokines function. Major classes of cytokines include interleukins (IL), interferons (IFN), tumor necrosis factors (TNF), and colonystimulating factors (CSF). Each class has several members (see Table 3–3). Cytokines act by binding to specific target cell receptors. When cytokines bind to their receptors on cells, the number of receptors is often increased as the cell is stimulated. Internal cellular signaling pathways become activated. The cell is no longer in a resting state and can have a new function. After cytokine binding, both the receptor and the cytokine become internalized, which induces the target cell to grow and differentiate. Differentiated cells have specialized functions such as secreting antibodies or producing enzymes. Immune cells and other host cells respond to cytokines and can react with chemoattraction, as well as antiviral, antiproliferation, and immunomodulation processes. Cytokines fine-tune the IS and also function as critical cell activators. In addition to the cytokines, other mediator substances of the IS, including chemokines, immunoglobulins, complement proteins, kinins, clotting factors, acute phase proteins, stress-associated proteins, and the fibrinolytic system, are cellular products that can have powerful cellular effects. Cytokines typically communicate between cells through the plasma. Chemokines are attractant molecules that interact between cells, immunoglobulins, and complement proteins and are important in destroying pathogens. Acute phase proteins and fibrinolytic proteins play a role in inflammation, a process that recruits appropriate cells to an immune site and modifies the vascular system. In addition to inflammation and cell-to-cell communication, some cytokines are immunosuppressive. One of the important chemokine receptors in blood banking is the Duffy antigen group present on RBCs. The lack of these antigens can prevent certain types of malaria parasites from infecting the host. The Duffy antigen may also modulate immune response by acting as a sink for extra cytokines of the IL-8 family.

Immune System Genetics Basic Concepts Individuals have a unique immune response based on their genetic inheritance, and there are familial patterns of susceptibility and resistance. In blood banking this is

2682_Ch03_045-076 28/05/12 2:32 PM Page 55

Chapter 3 Fundamentals of Immunology

important because not all transfusion recipients make antibodies to alloantigens on transfused RBCs. Responders are people who have a tendency based on their inheritance to make antibodies. The terms high responders and low responders describe individual responses to antigen challenges. When antigenic stimulation occurs, one B cell forms an antibody with a single specificity. During the lifetime of the cell, the cell can switch to make a different isotypic class of antibody that has the same antigen specificity. Isotype switching requires further DNA rearrangement in mature B cells. Class switching is dependent on antigenic stimulation and on the presence of cytokines released by T cells; this reflects the further adaptation of the immune response. Isotype switching is seen in blood banking when antibodies react at different temperatures and phases.

55

factor B. The genes for MHC classes I through III molecules are located on the short arm of chromosome 6 and are highly polymorphic in nature with multiple alleles.

Characteristics of Immunoglobulins Immunoglobulin (Ig), also called antibody, is a complex protein produced by plasma cells, with specificity to antigens (or immunogens), that stimulate their production. An Ig is a specific self protein produced by the host in response to a specific foreign, nonself protein, or other complex molecule not tolerated by the host. Immunoglobulins make up a high percentage of the total proteins in disseminated body fluids, about 20% in a normal individual. Antibodies bind antigen, fix complement, facilitate phagocytosis, and neutralize toxic substances in the circulation. Thus, antibodies have multiple functions, some more highly specialized and specific than others. Immunoglobulins are classified according to the molecular structure of their heavy chains. The five classifications are IgA (α [alpha] heavy chain), IgD (δ [delta] heavy chain), IgE (ε [epsilon] heavy chain), IgG (γ [gamma] heavy chain), and IgM (µ [mu] heavy chain). Table 3–5 illustrates some of the various differences in the classes of immunoglobulins, such as molecular weight, percentage in serum, valency (number of antigen-binding sites), carbohydrate content, half-life in the blood, and whether they exist as monomers or multimers. IgG is the most concentrated in serum, comprising approximately 80% of the total serum Ig; next is IgA, at about 13% (although it is the major Ig found in body secretions); IgM is 6%; IgD is 1%; and IgE is the least common, present at less than 1%.4

Advanced Concepts The major histocompatibility complex (MHC) is the region of the genome that encodes the human leukocyte antigen (HLA) proteins. (Refer to Chapter 21, “The HLA System.”) The MHC is critical in immune recognition and regulation of antigen presentation in cell-to-cell interactions, transplantation, paternity testing, and specific HLA patterns. It also correlates with susceptibility to certain diseases. HLA molecules are categorized into two classes: MHC classes I and II. Class I molecules are found on all nucleated cells except trophoblasts and sperm, and they play a key role in cytotoxic T-cell function. Class II molecules are found on antigen-presenting cells such as B lymphocytes, activated T cells, and the various dendritic cells. Class II molecules on APCs are essential for presenting processed antigen to CD4 T cells and are necessary for T-cell functions and B-cell help. In addition, there are class III molecules that encode complement components such as C2, C4, and

Immunoglobulin Structure All classes and subclasses of immunoglobulins (Igs) have a common biochemical structural configuration with similarities and are probably derived from a common evolutionary

Table 3–5 Characteristics of Serum Immunoglobulins CHARACTERISTIC

IgA

IgD

IgE

IgG

IgM

Heavy chain type

Alpha

Delta

Epsilon

Gamma

Mu

Sedimentation coefficient(s)

7–15*

7

8

6.7

19

Molecular weight (kD)

160–500

180

196

150

900

Biologic half-life (d)

5.8

2.8

2.3

21

5.1

Carbohydrate content (%)

7.5–9

10–13

11–12

2.2–3.5

7–14

Placental transfer

No

No

No

Yes

No

Complement fixation (classical pathway)

No

No

No

+

+++

Agglutination in saline

+

±

++++

Heavy chain allotypes

Am

None

None

Gm

None

Proportion of total immunoglobulin (%)

13

1

0.002

80

6

*May occur in monomeric or polymeric structural forms. d = days; kD = kilodaltons; 0 = negative reactivity; ± = weak reactivity; + = slight reactivity; +++ = strong reactivity; ++++ = very strong reactivity.

2682_Ch03_045-076 28/05/12 2:32 PM Page 56

56

PART I

Fundamental Concepts

immunoglobulins are known as the variable regions, because they are structured according to the great variation in antibody specificity. Structurally and functionally, the Fab fragments encompass the portions of the Ig from the hinge region to the amino terminal end and are the regions responsible for binding antigen (see Fig. 3–2). The domains of immunoglobulins are the regions of the light and heavy chains that are folded into compact globular loop structures (see Fig. 3–3). The domains are held together by intrachain covalent disulfide bonds; the V region of the domain specifies the variable region, and the C is the constant region. The domains are also specified according to light and heavy chains. Looking at one half of an Ig molecule, one domain (VL) is the variable region, one domain (CL) is in the constant region of each light chain, and one variable domain (VH) is on each heavy chain. The number of domains is determined by the isotype. There are three constant domains, CH1 to CH3, on the heavy chains of IgA, IgD, and IgG, and four constant domains, CH1 to CH4, on the heavy chains of IgE and IgM. The antigen-binding, or idiotypic, regions (which distinguish one V domain from all other V domains) are located within the three-dimensional structures formed by the VL and VH domains together. Certain heavy chain domains are associated with particular biological properties of immunoglobulins, especially those of IgG and IgM, and include complement fixation. They are identified with the CH2 domain and the CH3 domains, which serve as attachment sites for the FC receptor of monocytes and macrophages.

molecular structure with well-defined function. In Figure 3–2, the basic Ig structural unit is composed of four polypeptide chains: two identical light chains (molecular weights of approximately 22,500 daltons) and two identical heavy chains (molecular weights from approximately 50,000 to 75,000 daltons). In Figure 3–3, covalent disulfide bonding holds the light and heavy chains together, and the covalent disulfide linkages in Ig molecules provide greater structural strength than do hydrogen bonding and van der Waals forces. However, they limit the flexibility of the Ig molecule. The heavy chains are also interconnected by disulfide linkages in the hinge region of the molecule. Although there are five types of heavy chains, there are only two types of light chains: κ (kappa) and λ (lambda). Both types are found in all classes of immunoglobulins, regardless of heavy chain classification. Ig molecules are proteins and therefore have two terminal regions: the amino (-NH2) terminal and the carboxyl (-COOH) terminal. The carboxyl region of all heavy chains has a relatively constant amino acid sequence and is named the constant region. Like the heavy chain, the light chain also has a constant region. Due to certain common Ig structures, enzyme treatment yields specific cleavage products of defined molecular weight and structure. The enzyme papain splits the antibody molecule at the hinge region to give three fragments: one crystallizable FC fragment and two antigenbinding fragments, Fab. The FC fragment encompasses that portion of the Ig molecule from the carboxyl region to the hinge region and is responsible for complement fixation and monocyte binding by FC receptors on cells. The FC fragment on IgG antibody only is also responsible for placental transfer. In contrast to the carboxyl terminal regions, the amino terminal regions of both light and heavy chains of

Immunoglobulins Significant for Blood Banking

A Bi ntig nd e Si in n te g

N H2

NH 2

N H2

NH 2

All immunoglobulins can be significant for transfusion medicine; however, IgG, IgM, and IgA have the most significance

Hinge Region

S

S S

S

Heavy Chain Variable region Light Chain Variable region Heavy Chain Constant region Light Chain Constant region

S

S S

b

Fa

Fa b

S

Figure 3–2. Schematic representation of basic immunoglobulin structure. The inset shows formation of Fab and FC fragments after enzymatic cleavage of the IgG molecule by papain.

S

SS

COOH

COOH

S

SS

Fc

2682_Ch03_045-076 28/05/12 2:32 PM Page 57

Chapter 3 Fundamentals of Immunology

57

Heavy Chain

Light Chain

Hinge Region

Complement (C1q) Attachment Site

Attachment Site for Macrophage Fc Receptor Figure 3–3. Schematic illustration of the domain structure within the IgG molecule.

for the blood bank. Most clinically significant antibodies that react at body temperature (37°C) are IgG isotype and are capable of destroying transfused antigen-positive RBCs, causing anemia and transfusion reactions of various severities. IgM antibodies are most commonly encountered as naturally occurring antibodies in the ABO system and are believed to be produced in response to commonly occurring antigens like intestinal flora and pollen grains. (Refer to Chapter 6, “The ABO Blood Group System.”) Other blood groups such as Lewis, Ii, P, and MNS may also produce IgM antibodies, which usually react best at ambient temperature (22°C to 24°C). The primary testing problem encountered with IgM antibodies is that they can interfere with the detection of clinically significant IgG antibodies by masking their reactivity. Unlike IgG, IgM exists in both monomeric and polymeric forms (as pentamers) containing a J (joining) chain (Fig. 3–4).

Advanced Concepts The pentameric form can be dissociated through cleavage of covalent bonds interconnecting the monomeric subunits and the J chain by chemical treatment with sulfhydryl reducing reagents such as β-2-mercaptoethanol (2-ME) or dithiothreitol (DTT). These reagents can distinguish a mixture of IgM and IgG antibodies, because only IgM is removed by the use of these compounds; therefore, the removal allows unexpected IgG antibodies to be detected. IgG antibodies are significant in transfusion medicine, because they are the class of immunoglobulins that are made in response to transfusion with nonself antigens on blood products. IgG antibodies are important in hemolytic

disease of the newborn (HDN), because antibodies can be formed in response against alloantigens on fetal RBCs that enter the mother’s circulation, usually during delivery. HDN can be fatal. It is one area of medicine where immunohematology has provided prevention and treatment. Antibody screening, Rh typing, and passive anti-D antibody have prevented HDN from developing in D-negative mothers who give birth to D-positive babies. IgG has the greatest number of subclasses: IgG1, IgG2, IgG3, and IgG4, and all four are easily separated by electrophoresis. The small differences in the chemical structure

J Chain

IgM Monomer

Figure 3–4. Schematic representation of the pentameric configuration of the IgM immunoglobulin.

2682_Ch03_045-076 28/05/12 2:32 PM Page 58

58

PART I

Fundamental Concepts

within the constant regions of the gamma heavy chains designate the various subclasses, and the number of disulfide bonds between the two heavy chains in the hinge region of the molecule constitutes one of the main differences between subclasses. Functional differences between the subclasses include the ability to fix complement and cross the placenta (Table 3–6). IgG blood group antibodies of a single specificity are not necessarily one specific subclass; all four subclasses may be present, or one may predominate. For example, the antibodies to the Rh system antigens are mostly of the IgG1 and IgG3 subclasses, whereas anti-K (Kell), and anti-Fy (Duffy) antibodies are usually of the IgG1 subclass. Anti-Jk (Kidd) antibodies are mainly IgG3 and may account for the unusual nature of these different antibodies with regard to testing and clinical significance. The purpose for the existence of biological differences in subclass expression is still not completely understood. Especially important in blood banking, severe HDN has been most often associated with IgG1 antibodies.5 Like IgM, IgA exists in two main forms—a monomer and polymer form—as dimers or trimers composed of two or three identical monomers, respectively, joined by a J chain. IgA is located in different parts of the IS, depending on subclass. Serum IgA is found in both monomeric and polymeric forms; however, secretory IgA is usually found in the mucosal tissues of the body. Its polymer form acquires a glycoprotein secretory component as it passes through epithelial cell walls of mucosal tissues and appears

in nearly all body fluids. IgA is important in immunohematology, because about 30% of anti-A and anti-B antibodies are of the IgA class (the remaining percentages are IgM and IgG).6 Also, anti-IgA antibodies can cause severe anaphylaxis if IgA are transfused in plasma products to patients who are deficient in IgA. Another reason for the importance of IgA is that it can increase the effect of IgGinduced RBC hemolysis.7 IgE is normally found only in monomeric form in trace concentrations in serum, about 0.004% of total immunoglobulins, and is important in allergic reactions. The FC portion of the IgE molecule attaches to basophils and mast cells and facilitates histamine release when an allergen binds to the Fab portion of the molecule and cross-links with a second molecule on the cell surface. Histamine is critical for bringing about an allergic reaction. Although hemolytic transfusion reactions are not caused by IgE, urticaria may occur because of the presence of IgE antibodies. Because IgE causes transfusion reactions by release of histamines, patients who have several allergic reactions to blood products can be pretreated with antihistamines to counteract the response when receiving blood products.2 IgD, present as less than 1% of serum immunoglobulins, appears to have functions that deal primarily with maturation of B cells into plasma cells. IgD is usually bound to the membrane of immature B cells. Therefore, IgD may be necessary for regulatory roles during B-cell differentiation and antibody production but is probably the least significant for blood banking.8

Immunoglobulin Variations

Table 3–6 Biological Properties of IgG Subclasses CHARACTERISTIC

IgG1

IgG2

IgG3

IgG4

Proportion of total serum IgG (%)

65–70

23–28

4–7

3–4

Complement fixation (classic pathway)

++

+

+++

Binding to macrophage FC receptors

+++

++

+++

±

Ability to cross placenta

+

±

+

+

• Anti-Rh

++

+

±

• Anti-factor VII

+

• Anti-dextran

+

• Anti-Kell

+

• Anti-Duffy

+

• Anti-platelet

+

Biological half-life (days)

21

21

7–8

21

Dominant antibody activities:

0 = negative reactivity; ± = weak (or unusual) reactivity; + = slight (or usual) reactivity; ++ = moderate (or more common) reactivity; +++ = strong reactivity.

There are three main types of antibody-inherited variation: isotype, allotype, and idiotype. Isotype variation (or class variation) refers to variants present in all members of a species, including the different heavy and light chains and the different subclasses. All humans have the same Ig classes and subclasses. Allotypic variation is present primarily in the constant region; not all variants occur in all members of a species. Idiotypic variation, which determines the antigen-binding specificity (or complementary determining regions, [CDRs]) of antibodies and T-cell receptors, is found only in the variable (and hypervariable) regions and is specific for each antibody molecule. The allotypes of a growing fetus may cause the maternal IS to become immunized to paternal allotypic determinants on fetal immunoglobulins.4 Just as alloimmunization can occur during pregnancy, it can occur from transfusions, especially in patients who have received multiple transfusions of blood, plasma, or gamma globulin. Idiotypes can be seen as nonself because they are often present at concentrations too low to induce selftolerance. Idiotypes are determined by the antigens that react with them and exist in a type of equilibrium with anti-idiotypic antibodies. The presence of antigen disrupts this equilibrium and may be important in controlling an immune response.

Immunoglobulin FC Receptors Macrophages and monocytes have receptors for the attachment of IgG and can bind the CH3 domain of the FC portion.

2682_Ch03_045-076 28/05/12 2:32 PM Page 59

Chapter 3 Fundamentals of Immunology

Only the IgG1 and IgG3 subclasses are capable of attachment to phagocytic receptors. This is one way that incompatible RBCs coated with IgG antibody are removed by phagocytosis. The other phagocytic cells with FC receptors include neutrophils, NK cells, and mature B cells.4,9

Complement System Basic Concepts The complement system, or complement, is a complex group of over 20 circulating and cell membrane proteins that have a multitude of functions within the immune response. Primary roles include direct lysis of cells, bacteria, and enveloped viruses as well as assisting with opsonization to facilitate phagocytosis. Another role is production of peptide fragment split products, which play roles in inflammatory responses such as increased vascular permeability, smooth muscle contraction, chemotaxis, migration, and adherence. Complement components circulate in inactive form as proenzymes, with the exception of factor D of the alternate pathway. The complement proteins are activated in a cascade of events through three main pathways: the classical, alternative, and lectin pathways. The three pathways converge at the activation of the component C3. The classical pathway is activated by the binding of an antigen with an IgM, IgG1, or IgG3 antibody. The alternative pathway is activated by high molecular weight molecules with repeating units found on the surfaces of target cells. The lectin pathway is activated by attachment of plasma mannose-binding lectin (MBL) to microbes. MBL in turn activates proteins of the classical pathway.

Advanced Concepts Complement components are sequentially numbered C1 through C9, but this refers to their discovery date, not to their activation sequence. The four unique serum proteins of the alternative pathway are designated by letters: factor B, factor D, factor P (properdin), and IF (initiating factor). Some activation pathways require Ca2+ and Mg2+ cations as cofactors for certain components. In certain nomenclature, complement components that are active are designated by a short bar placed over the appropriate number or letter. The cleavage products of complement proteins are distinguished from parent molecules by suffixes such as C3a and C3b. The complement system is able to modulate its own reactions by inhibitory proteins such as C1 inhibitor (C1INH), factor H, factor I, C4-binding protein (C4BP), anaphylatoxin inactivator, anaphylatoxin inhibitor, membrane attack complex (MAC) inhibitor, and C3 nephritic factor (NF). This regulation of complement is important so that complement proteins do not destroy healthy host cells and inflammation is controlled. The evaluation of C3b and C3d complement components in transfusion medicine testing procedures is useful in the investigation of hemolytic transfusion reactions and autoimmune hemolytic anemias.

59

Classical Complement Pathway The activation of the classical complement pathway is initiated when antibody binds to antigen. This allows the binding of the complement protein C1 to the FC fragment of an IgM, IgG1, or IgG3 subclass antibody. Complement activation by IgG antibody depends on concentration of cell surface antigen and antigen clustering, in addition to antibody avidity and concentration. IgM is large and has FC monomers close to each other on one immunoglobulin molecule; therefore, only one IgM molecule is necessary to activate complement. The C1 component is actually a complex composed of three C1 subunits, C1q, C1r, and C1s, which are stabilized by calcium ions. Without calcium present, there is no stabilization of the C1q, r, s complex, and complement is not activated. In the C1 complex bound to antigen antibody, C1q is responsible for catalyzing the C1r to generate activated C1s. Activated C1s is a serine-type protease. The C1q, r, s complex (actually as a C1q[r, s]2 unit) acts on C2 and C4 to form C4b2a. C4b2a uses component C3 as a natural substrate. Byproducts that result from the activation of the classical sequence include C3a; C4b, which binds to the cell surface; C4a, which stays in the medium and has modest anaphylatoxin activity; and C3b, which attaches to the microbial surface. Note that complement fragments that have the b type are usually bound to membranes, whereas the a fragments often have anaphylatoxic activity. Human RBCs have CR1 receptors for C4d and C3b, and some of the cleavage products will attach to the RBC membrane. Eventually these fragments are further degraded to C4d and C3d through the action of C4BP, factor H (which binds C3b), and factor I (which degrades both C4b and C3b). Some of C3b binds to the C4b2a complex, and the resulting C4b2a3b complex functions as a C5 convertase. The C5 convertase then acts on C5 to produce C5a (a strong stimulator of anaphylatoxins) and C5b, which binds to the cell membrane and recruits C6, C7, C8, and C9 to the cell membrane. When C5b along with C6, C7, C8, and C9 are bound, the membrane attack complex forms; this causes cell lysis. Figure 3–5 shows the sequential activation of the complement system via the classical and alternative pathways. Figure 3–6 illustrates the mechanism of antibody-dependent cell-mediated cytotoxicity (ADCC).

Alternative Complement Pathway The alternative pathway is older in evolution and allows complement to be activated without acquired immunity. The alternative pathway is activated by surface contacts with complex molecules and artificial surfaces such as dialysis membranes and dextran polymers. There are four important proteins in this pathway: factor D, factor B, properdin, and C3. In this pathway, complement component factor D is analogous to C1s in the classical pathway; factor B is analogous to C2; and the cleavage product C3b is analogous to C4. Also, factor C3bBbP is analogous to C4b2a, and C3b2BbP is analogous to C4b2a3b in the classical pathway. Activation of the alternative pathway requires that a C3b molecule be bound to the surface of a target cell. Small

2682_Ch03_045-076 28/05/12 2:32 PM Page 60

60

PART I

Fundamental Concepts ALTERNATIVE PATHWAY

CLASSIC PATHWAY

C4b, 2C

MEMBRANE ATTACK MECHANISM C5b67

C5b6789

Figure 3–5. Schematic diagram illustrating the sequential activation of the complement system via the classical and alternative pathways.

CELL LYSIS

amounts of C3b are generated continuously, owing to the spontaneous hydrolytic cleavage of the C3 molecule. When C3b encounters normal cells, it is rapidly eliminated through the combined interactions of factors H and I. The accumulation of C3b on microbial cell surfaces is associated with attachment of C3b to factor B. The complex of C3b and factor B is then acted on by factor D. As a result of this action, factor B is cleaved, yielding a cleavage product known as Bb. The C3bBb complex is stabilized by the presence of

IgG Antibody

properdin (P), yielding C3bBbP. This complex cleaves C3 into additional C3a and C3b. C3b, therefore, acts as a positive feedback mechanism for driving the alternative pathway. The C3b2BbP complex acts as a C5 convertase and initiates the later steps of complement activation (see Fig. 3–5).

Lectin Complement Pathway The third pathway of activation, the lectin pathway, is activated by the attachment of MBL to microbes. The subsequent reactions are the same as those of the classical pathway. Remember that all three methods of activation lead to a final common pathway for complement activation and membrane attack complex (MAC) formation.

Lysed Target Cell

Membrane Attack Complex Red Cell Antigenic Determinant Site

Effector Cell (Monocyte) C3b Receptor

Fc Receptor

Figure 3–6. Schematic representation of the mechanism of antibody-dependent cell-mediated cytotoxicity (ADCC). Note the role of effector cell surface receptors for the FC fragment of IgG.

The final step of complement activation is the formation of the MAC, which is composed of the terminal components of the complement sequence. There are two ways in which the MAC is initiated. In either classical or alternative pathways, the formation of C5 convertase is necessary. In the activation of the classical pathway, the MAC is initiated by the enzymatic activity of component C4b2a3b on C5. In the alternative pathway, it is C3b2Bb that has the ability to cleave C5. The next step in either pathway is the same. Component C5 is split into the fragments C5a (a potent anaphylatoxin) and C5b; the C5b fragment attaches to cell membranes and can continue the complement cascade by initiating the membrane attachment of C6, C7, and C8. After the attachment of C9

2682_Ch03_045-076 28/05/12 2:32 PM Page 61

Chapter 3 Fundamentals of Immunology

to the C5b678 complex, a small transmembrane channel or pore is formed in the lipid bilayer of the cell membrane, and this allows for osmotic lysis and subsequent death of the cell.

Binding of Complement by RBC Antibodies Basic Concepts Disruption in the activation of either complement pathway can result in damage to the host’s cells. Transfusion medicine specialists are concerned with the formation of antibodies with complement capacity that can bring about the destruction of RBCs. Recall that in order to initiate activation, C1 molecules bind with two adjacent Ig FC regions. A pentameric IgM molecule provides two FC regions side by side, thereby binding complement. A monomeric IgG molecule, on the other hand, binds C1q less efficiently, and two IgG molecules are needed in close proximity to bind complement. For example, as many as 800 IgG anti-A molecules may need to attach to one adult group A RBC to bind a single C1 molecule, so there is little complement activation by IgG anti-A immunoglobulins.4 Antibodies against the Rh antigens usually do not bind complement due to the low level of Rh antigens on RBC surfaces. Antibodies to the Lewis blood group system are generally IgM, and they can activate complement but rarely cause hemolytic transfusion reactions due to their low optimal reactivity temperature. Therefore, in blood banking, with the exception of the ABO system, only a few antibodies activate the complement sequence that leads to complement mediated intravascular hemolysis. However, extravascular hemolysis usually occurs as a result of antibody coating of RBCs, and the split products of complement activation can stimulate the reticuloendothelial system and cause anaphylatoxic effects. Antibody-coated RBCs, either self or nonself, are removed by cells of the mononuclear phagocyte system and by the cells lining the hepatic and splenic sinusoids. These phagocytic cells are able to clear antibody-coated RBCs because they have cell surface receptors for complement CR1 (C3b) and Ig FC receptors (see Fig. 3–6). IgM-coated RBCs are not eliminated through FC receptor–mediated phagocytosis, but if erythrocytes are coated with IgG and complement, they will be cleared rapidly from circulation by monocytes and macrophages. If RBCs are coated with only C3b, they may not be cleared but only sequestered temporarily.

by several biochemical and physical characteristics of the immunogen. Properties such as size, complexity, conformation, charge, accessibility, solubility, digestibility, and biochemical composition influence the amount and type of immune response (Box 3–2). Molecules that are too small cannot stimulate antibody production. Immunogens having a molecular weight (MW) less than 10,000 daltons (D), for example, are called haptens and usually do not elicit an immune response on their own; however, coupled with a carrier protein having a MW greater than 10,000 D, they can produce a reaction. Antibodies and cellular responses are very specific for an antigen’s physical conformation as opposed to its linear sequence. Overall charge is important, as antibody response is also formed to the net charge of a molecule, whether it is positive, negative, or neutral. Obviously, an antigen must be seen by the IS, and so the accessibility of epitopes influences the immune response. Also, antigenic substances that are less soluble are less likely to elicit an immune response. The biochemical composition of the stimulus plays a role in immune stimulation. Remember that RBC antigens are very diverse in structure and composition and may be proteins (such as the Rh, M, and N blood group substances) or glycolipids (such as the ABH, Lewis, Ii, and P blood group substances). Human leukocyte antigens (HLAs) are glycoproteins. Because of these differences in structure, conformation, and molecular nature, not all blood group substances are equally immunogenic in vivo (Table 3–7).

Characteristics of Blood Group Antibodies There are many different and important characteristics of blood group antibodies, such as whether they are polyclonal or monoclonal, naturally occurring or immune, and alloantibodies or autoantibodies.

Polyclonal and Monoclonal Antibodies In laboratory testing, there are two types of antibody (reagent antibodies are called antisera) that are available for use; they are manufactured differently and have different properties. An antigen usually consists of numerous epitopes, and it is the epitopes and not the entire antigen that a B cell is

BOX 3–2

Characteristics of Antigens: Properties That Influence Immune Response Characteristics of Antigens The immune response is initiated by the presentation of an antigen (initiates formation of and reacts with an antibody) or immunogen (initiates an immune response). The term antigen is more commonly used in blood banking because the primary testing is the detection of antibodies to blood group antigens. The immune reaction to any immunogen, including antigens, is determined by the host response and

61

• • • • • • • •

Size Complexity Conformation Charge Accessibility Solubility Digestibility Chemical composition

2682_Ch03_045-076 28/05/12 2:32 PM Page 62

62

PART I

Fundamental Concepts

Table 3–7 Relative Immunogenicity of Different Blood Group Antigens

today are monoclonal in nature or are a blend of monoclonal antisera.

BLOOD GROUP ANTIGEN

BLOOD GROUP SYSTEM

Naturally Occurring and Immune Antibodies

D (Rho)

Rh

50

K

Kell

5

c (hr’)

Rh

2.05

E (rh’’)

Rh

1.69

k

Kell

1.50

e (hr’’)

Rh

0.56

Fya

Duffy

0.23

C (rh’)

Rh

0.11

Jka

Kidd

0.07

S

MNSs

0.04

Jkb

Kidd

0.03

s

MNSs

0.03

IMMUNOGENICITY (%)*

Adapted from Kaushansky, K, et al: Williams Hematology, 8th ed. McGraw-Hill Professional, New York, 2010. *Percentage of transfusion recipients lacking the blood group antigen (in the first column) who are likely to be sensitized to a single transfusion of red cells containing that antigen.

stimulated to produce antibody against. Therefore, these different epitopes on a single antigen induce the proliferation of a variety of B-cell clones, resulting in a heterogeneous population of serum antibodies. These antibodies are referred to as polyclonal or serum antibodies and are produced in response to a single antigen with more than one epitope. In vivo, the polyclonal nature of antibodies improves the immune response with respect to quality and quantity. Antibodies against more than one epitope are needed to give immunity against an entire antigen, such as a pathogen. However, this diversity is not optimal in the laboratory, and in vitro reagents produced by animals or humans can give confusing test results. Consistency and reliability are needed in laboratory testing, and polyclonal sera can vary in antibody concentration from person to person and animal to animal. Sera from the same animal can also vary somewhat, depending on the animal’s overall condition. Individual sera also differ in the serologic properties of the antibody molecules they contain, the epitopes they recognize, and the presence of additional nonspecific or crossreacting antibodies. One way to avoid this problem is to use monoclonal antibodies produced by isolating individual B cells from a polyclonal population and propagating them in cell culture with hybridoma technology. The supernatant from the cell culture contains antibody from a single type of B cell, clonally expanded, and therefore has the same variable region and a single epitope specificity. This results in a monoclonal antibody suspension. Monoclonal antibodies are preferred in testing because they are highly specific, well characterized, and uniformly reactive. Most reagents used

There are two types of antibodies that concern blood banking: one is naturally occurring and the other is immune. Both are produced in reaction to encountered antigens. RBC antibodies are considered naturally occurring when they are found in the serum of individuals who have never been previously exposed to RBC antigens by transfusion, injection, or pregnancy. These antibodies are probably produced in response to substances in the environment that resemble RBC antigens such as pollen grains and bacteria membranes. The common occurrence of naturally occurring antibodies suggests that their antigens are widely found in nature and have a repetitive complex pattern. Most naturally occurring antibodies are IgM cold agglutinins, which react best at room temperature or lower, activate complement, and may be hemolytic when active at 37°C. In blood banking, the common naturally occurring antibodies react with antigens of the ABH, Hh, Ii, Lewis, MN, and P blood group systems. Some naturally occurring antibodies found in normal serum are manufactured without a known environmental stimulus.10 In contrast to natural antibodies, RBC antibodies are considered immune when found in the serum of individuals who have been transfused or who are pregnant. These antigens have a molecular makeup that is unique to human RBCs. Most immune RBC antibodies are IgG antibodies that react best at 37°C and require the use of antihuman globulin sera (Coombs’ sera) for detection. The most common immune antibodies encountered in testing include those that react with the Rh, Kell, Duffy, Kidd, and Ss blood group systems.10

Unexpected Antibodies Naturally occurring anti-A and anti-B antibodies are routinely detected in human serum and depend on the blood type of the individual. Blood group A has anti-B; blood group B has anti-A; blood group O has both and anti-A, B. Blood group AB has neither antibody present in their serum. These naturally occurring antibodies, or isoagglutinins, are significant and useful in blood typing. They are easily detected by use of A and B reagent RBCs with a direct agglutination technique. In normal, healthy individuals, anti-A and anti-B are generally the only RBC antibodies expected to be found in a serum sample. People with an IS that does not function normally may not have the expected naturally occurring antibodies. All other antibodies directed against RBC antigens are considered unexpected and must be detected and identified before blood can be safely transfused, no matter their reaction strength or profile. The reactivity of unexpected antibodies is highly varied and unpredictable, as they may be either isotype IgM or IgG; rarely, both may be present in the same sample. These antibodies may be able to hemolyze, agglutinate, or sensitize RBCs. Some antibodies require special reagents to enhance their reactivity and detection, especially if more than one antibody occurs in

2682_Ch03_045-076 28/05/12 2:32 PM Page 63

Chapter 3 Fundamentals of Immunology

the sample. Due to the enormous polymorphism of the human population, a diversity of RBC alleles and antigens exist, requiring a variety of standardized immunologic techniques and reagents for their detection and identification. The in vitro analysis of unexpected antibodies involves the use of antibody screening procedures to optimize antigenantibody reactions. The majority of these procedures include reacting unknown serum from a donor or patient sample with known reagent cells at various amounts of time, temperature, and media. All routine blood bank testing requires the use of samples for both expected and unexpected antibodies.

Alloantibodies and Autoantibodies Antibodies can be either alloreactive or autoreactive. Alloantibodies are produced after exposure to genetically different, or nonself, antigens, such as different RBC antigens after transfusion. Transfused components may elicit the formation of alloantibodies against antigens (red cell, white cell, and platelets) not present in the recipient. Autoantibodies are produced in response to self-antigens. They can cause reactions in the recipient if they have a specificity that is common to the transfused blood. Some autoantibodies do not have a detectable specificity. Autoantibodies can react at different temperatures, and cold or warm autoantibodies may both be present. Patients with autoantibodies frequently have autoimmune diseases and may require considerable numbers of blood products and special techniques to find compatible units. A potentially serious problem for blood bankers is transfused patients who have alloantibodies that are no longer detectable in the patient’s plasma or serum. If these individuals are transfused with the immunizing antigen again, they will make a stronger immune response against those RBC antigens, which can cause severe and possibly fatal transfusion reactions. These recipients will then have a positive autocontrol or direct antiglobulin test (DAT), which may also be referred to as the direct Coombs’ test. This is why the previous history of any patient is a critical part of the testing. Autoantibodies can be removed from RBCs by special adsorption and elution techniques and then tested against reagent RBCs. Remember that in order to transfuse blood safely, the identity of antibodies should be determined and recorded.

Characteristics of Antigen-Antibody Reactions There are many complex properties of antigen and antibody reactions that influence serologic and other testing methods involving antibodies. The antigen-binding site of the antibody molecule is uniquely designed to recognize a corresponding antigen; this antibody amino acid sequence cannot be changed without altering its specificity. The extent of the reciprocal relationship, also called the fit between the antigen and its binding site on the antibody, is often referred to as a lock and key mechanism. Factors influencing antigen-antibody reactions include intermolecular binding forces, antibody properties, host factors, and tolerance.

63

Intermolecular Binding Forces Intermolecular binding forces such as hydrogen bonding, electrostatic forces, van der Waals forces, and hydrophobic bonds are all involved in antigen-antibody binding reactions. Stronger covalent bonds are not involved in this reaction, although they are important for the intramolecular conformation of the antibody molecule. Hydrogen bonds result from weak dipole forces between hydrogen atoms bonded to oxygen or nitrogen atoms in which there is incomplete transfer of the electronic energy to the more electronegative oxygen or nitrogen. When two atoms with dipoles come close to each other, there is a weak attraction between them. Although hydrogen bonds are singularly weak, many of them together can be strong. They are found in complex molecules throughout the human body. Electrostatic forces result from weak charges on atoms in molecules that have either a positive or negative overall charge (like charges repel and unlike charges attract). This is seen in the formation of salt bridges. Van der Waals forces are a type of weak interaction between atoms in larger molecules. Hydrophobic (water-avoiding) bonds result from the overlap of hydrophobic amino acids in proteins. The hydrophobic amino acids bury themselves together to avoid water and salts in solution. The repulsion of these amino acids to prevent contact with water and aqueous solutions can be very strong collectively. In addition, there are hydrophilic (water-loving) bonds that allow for the overlap of amino acids that are attracted to water. Hydrophobic and hydrophilic bonds repel each other, and these repulsive forces also play a role in the formation of the antigen-antibody bond. All of these bonds affect the total conformation and strength of antigen-antibody reactions and IS molecules.

Antibody Properties There are many important terms that refer to the properties of antibody reactions. The first is antibody affinity; it is often defined as the strength of a single antigen-antibody bond produced by the summation of attractive and repulsive forces. The second term is avidity, which is used to express the binding strength of a multivalent antigen with antisera produced in an immunized individual. Avidity, therefore, is a measure of the functional affinity of an antiserum for the whole antigen and is sometimes referred to as a combination of affinities. Avidity can be important in blood banking because high-titer, low-avidity antibodies exhibit low antigenbinding capacity but still show reactivity at high serum dilutions.11 The specificity of an antiserum (or antibody) is one of its most important characteristics and is related to its relative avidity for antigen. Antibody specificity can be further classified as a specific reaction, cross-reaction, or no reaction (Fig. 3–7). A specific reaction implies reaction between similar epitopes. A cross-reaction results when certain epitopes of one antigen are shared by another antigen and the same antibody can react with both antigens. No reaction occurs when there are no shared epitopes.

2682_Ch03_045-076 28/05/12 2:32 PM Page 64

64

PART I

Fundamental Concepts

Specific Reaction

Cross-Reaction

No Reaction

Immunizing Antigen Determinant Shared No Shared Determinant Figure 3–7. Types of antigen-antibody reactions: specific reaction, cross-reaction, and no reaction.

In some instances, an individual’s race may be a factor in susceptibility to certain diseases. A dramatic example of this is seen in malaria infection. The majority of African Americans who do not inherit the Duffy blood system antigens Fya or Fyb are resistant to malarial invasion with Plasmodium knowlesi and Plasmodium vivax. The absence of these antigens may make these individuals ideal donors for those who have developed Duffy system antibodies. (Refer to Chapter 8, “Blood Group Terminology and the Other Blood Groups.”) This illustrates once again the importance of the historical record of the patient or donor.

Tolerance In addition, there is the valency of an antibody, which is the number of antigen-binding sites on an antibody molecule or the number of antibody binding sites on an antigen. Antigens are usually multivalent, but antibodies are usually bivalent. IgM and IgA antibodies can have higher valences due to the multimeric nature of some of their structures. Because the biochemistry controlling the forces of antibody binding are well understood, the influence of these forces can be manipulated by using various reagents and methods to enhance the reactivity of certain RBC antigens with antibodies. When more than one antibody is present in a blood bank sample, it is often necessary to use special techniques to identify all the antibodies. These techniques and reagents were developed with an understanding of antibody reactivity.

Host Factors Various host factors play a key role in an individual’s immune response (Box 3–3). These factors are important in the host’s overall immune response and in various specific immune reactions. Each individual’s immune system is unique and determines how that individual is able to resist disease. Host factors include nutritional status, hormones, genetic inheritance, age, race, sex, physical activity level, environmental exposure, and the occurrence of disease or injury. It is also believed that immune function decreases as age increases; this may be one reason why so many diseases such as cancer and autoimmune conditions are seen at a later time in life. A decrease in antibody levels in older individuals may result in falsenegative reactions, especially in reverse ABO blood typing.

BOX 3–3

Host Factors: Properties of the Host That Influence Immune Response • • • • • • • •

Nutritional status Hormones Genetics Age Race Exercise level Disease Injury

Advanced Concepts Tolerance is defined as the lack of an immune response or an active immunosuppressive response. It has been observed post-transfusion for many years, but its mechanism is still unclear. Tolerance can be either naturally occurring or experimentally induced. Exposure to an antigen during fetal life usually produces tolerance to that antigen. An example of this type of tolerance is found in the chimera, an individual who receives an in utero cross-transfusion of ABO-incompatible blood from a dizygotic (fraternal) twin.2 The chimera does not produce antibodies against the A and B antigen of the twin, and the ABO group of such an individual may appear as a testing discrepancy. The induction of tolerance is used to prevent D-negative mothers from developing anti-D antibodies after delivering Rh-positive infants. When a D-negative woman gives birth to a D-positive infant, she is exposed to D-positive RBCs, most of which occurs during delivery. Approximately 50% to 70% of Rh-negative mothers develop anti-D antibodies on first exposure to D-positive cells. These antibodies can result in HDN upon later pregnancies with a D-positive fetus. Use of passive immunization to prevent the formation of these antibodies can prevent HDN. This is accomplished by administering IgG Rh-immune globulin (RHIG) within 48 to 72 hours after the birth of the infant. About 25% to 30% of D-negative individuals are nonresponders and do not produce anti-D antibodies, even when subjected to repeated exposure to D-positive cells. Because it is not known who will respond, it is recommended that all D-negative mothers who deliver D-positive newborns receive RHIG to prevent immunization.

Detection of RBC Antigen-Antibody Reactions Basic Concepts Various factors influence detection of RBC antigen-antibody reactions. These include having a correct sample and the proper reagents performing the correct test and understanding how the test should be done and interpreted.

2682_Ch03_045-076 28/05/12 2:32 PM Page 65

Chapter 3 Fundamentals of Immunology

Blood Samples Required for Testing One of the most important steps in obtaining the correct and valid results of an analytical or diagnostic test is to have the correct sample. Different tests in the blood bank may require different samples. Some tests require the use of serum to ensure that adequate amounts of viable complement are available for fixation by blood group antibodies. Serum is obtained when no anticoagulant is used in the sample collection tube. The sample clots and is centrifuged to separate the clotted cells and the liquid serum fraction. An anticoagulated sample would not be conducive to complement activation studies, because anticoagulants bind divalent Ca2+ and Mg2+ ions and inhibit complement activity. The commonly used anticoagulant ethylenediaminetetraacetic acid (EDTA) at a ratio of 2 mg to 1 mL of serum will totally inhibit complement activation by binding calcium and, to a lesser extent, magnesium. Another anticoagulant, sodium heparin, inhibits the cleavage of C4. These problems can be avoided by using serum instead of plasma for blood bank procedures that require fresh complement. Currently, however, plasma is used routinely in place of serum. Years of testing with both samples have shown that for most tests, plasma is comparable to serum. Plasma samples are preferred for DAT and elution studies because they lack fibrin strands, which can cause false-positives. Serum should be removed as soon as possible from a clotted blood sample. If testing cannot begin immediately, then serum should be removed and stored at 4°C for no longer than 48 hours. After this time, serum should be frozen at –50°C or lower to retain complement activity. The complement system may become activated during storage of preserved RBC products. For example, in citrate phosphate dextrose adenine (CPDA-1)–preserved RBCs, activation of the alternate pathway can be caused by contact of plasma C3 with plastic surfaces of blood bags. This may cause hemolysis that will become visible as the RBCs settle upon storage.12

Traditional Laboratory Testing Methods The various complex immunologic responses that are important to blood banking have been studied by a number of immunologic methods. These in vitro testing methods were developed with an understanding of the biochemistry and biophysics of the IS. Many of the methods used today are modifications of previous blood bank techniques or more generalized immunologic testing methods that have been adapted to the needs of immunohematology laboratories. The routine methods used today have to be highly efficient to meet clinical laboratory requirements.

Advanced Concepts Many different types of tests are available, and it is important to be familiar with the different purposes of each. In vitro testing for the detection of antigens or antibodies may be accomplished by commonly used techniques, including

65

hemagglutination (a special type of agglutination), precipitation, agglutination inhibition, and hemolysis. Other techniques that quantify antigen or antibody with the use of a radioisotope, enzyme, or fluorescent label—such as radioimmunoassay (RIA), enzyme-linked immunosorbent assay (ELISA) or enzyme immunoassay (EIA), Western blotting (WB), and immunofluorescence (IF)—may be used in automated or semiautomated blood banking instrumentation.2 These techniques are very important in testing for viral pathogens in donor units and patient samples. Recently, blood bank automated methods for the typing of whole blood units and patient samples have become more popular and may become routine in the near future. In most transfusion laboratory testing, hemagglutination reactions are the major technique used. Hemagglutination methods for the analysis of blood group antigen-antibody responses and typing for ABO, Rh, and other blood group antigens is accomplished by red cell agglutination reactions. Agglutination is a straightforward process and can be shown to develop in two stages. In the first stage, sensitization, antigen binding to the antibody occurs. Epitopes on the surfaces of RBC membranes combine with the antigencombining sites (Fab region) on the variable regions of the immunoglobulin heavy and light chains. Antigen and antibody are held together by various noncovalent bonds, and no visible agglutination is seen at this stage. In the second stage, a lattice-type structure composed of multiple antigen-antibody bridges between RBC antigens and antibodies is formed. A network of these bridges forms, and visible agglutination is present during this stage. The development of an insoluble antigen-antibody complex, resulting from the mixing of equivalent amounts of soluble antigen and antibody, is known as a precipitation reaction. Agglutination inhibition is a method in which a positive reaction is the opposite of what is normally observed in agglutination. Agglutination is inhibited when an antigenantibody reaction has previously occurred in a test system. The antigen and antibody cannot bind because another substrate has been added to the reaction mixture and blocks the formation of the agglutinates. Inhibition reactions are used in secretory studies to determine whether soluble ABO substances are present in body fluids and secretions. The secreted substrate can combine with the antibody and block RBC antigen-antibody reactions. People who have blood group antibodies in their body fluids are called secretors. Hemolysis represents a strong positive result and indicates that an antigen-antibody reaction has occurred in which complement has been fixed and RBC lysis occurs. The Lewis blood group antibodies anti-Lea and anti-Leb may be regarded as clinically significant if hemolysis occurs in their in vitro testing reactions. RIA, ELISA (or EIA), WB, and IF techniques are immunologic methods based on detection and quantification of antigen or antibody by the use of a radioisotope, enzyme, or fluorescent labels. Either the antigen or the antibody can be labeled in these tests. These techniques measure the interaction of the binding of antigen with antibody and

2682_Ch03_045-076 28/05/12 2:32 PM Page 66

66

PART I

Fundamental Concepts

are extremely sensitive. Most of these techniques employ reagents that use either antigen or antibody, which is bound in a solid or liquid phase in a variety of reaction systems ranging from plastic tubes or plates to microscopic particles or beads. These methods use a separation system and washing steps to isolate bound and free fractions and a detection system to measure the amount of antigen-antibody interaction. The values of unknown samples are then calculated from the values of standards of known concentration.

Factors That Influence Agglutination Reactions Basic Concepts Various factors can influence reactivity of antigen-antibody RBC agglutination reactions. Typical of most biochemical reaction systems, agglutination reactions are influenced by the concentration of the reactants (antigen and antibody) and by factors such as pH, temperature, and ionic strength. The surface charge, antibody isotype, RBC antigen dosage, and the use of various enhancement media, antihuman globulin reagents, and enzymes are all important in antigenantibody reactions. The most important factors are discussed in the following sections. Centrifugation Centrifugation is an effective way to enhance agglutination reactions because it decreases reaction time by increasing the gravitational forces on the reactants and bringing reactants closer together. High-speed centrifugation is one of the most efficient methods used in blood banking. Under the right centrifugation conditions, sensitized RBCs overcome their natural repulsive effect (zeta potential) for each other and

agglutinate more efficiently. Having RBCs in closer physical proximity allows for an increase in antigen-antibody lattice formation, which results in enhanced agglutination.

Antigen-Antibody Ratio Antigen and antibody have optimal concentrations; in ideal reactive conditions, an equivalent amount of antigen and antibody binds. Any deviation from this decreases the efficiency of the reaction and a loss of the zone of equivalence between antigen and antibody ratio that is necessary for agglutination reactions to occur. An excess of unbound immunoglobulin leads to a prozone effect, and a surplus of antigen leads to a postzone effect (Fig. 3–8). In either situation, the lattice formation and subsequent agglutination may not occur, which can give false-negative results. If this is suspected, simple steps can be taken to correct it. If the problem is excessive antibody, the plasma or serum may be diluted with the appropriate buffer. The problem of excessive antigen can be solved by increasing the serum-to-cell ratio, which tends to increase the number of antibodies available to bind with each RBC. Therefore, antigen-antibody test systems can be manipulated to overcome the effects of excessive antigen or antibody. Another reason antigen amount may be altered is due to weak expression of antigen on RBCs (dosage effect). Weak expression occurs as a result of the inheritance of genotypes that give rise to heterozygous expression of RBC antigens and resultant weaker phenotypes. For example, M-positive RBCs from an individual having the genotype MM (homozygous) have more M antigen sites than M-positive cells from an individual having the MN (heterozygous) genotype. In the Kidd system, Jka homozygous inheritance has greater RBC antigen expression than Jka heterozygous. The same is true for Jkb homozygous and heterozygous expression. In the Rh system, the C, c, E, and e antigens also show dosage

Figure 3–8. Schematic representation of the effects of varying concentrations of antigen and antibody on lattice formation.

Antibody Excess (Prozone)

Equivalence (Optimum Proportions of Antigen and Antibody)

Antigen Excess (Postzone)

2682_Ch03_045-076 28/05/12 2:32 PM Page 67

Chapter 3 Fundamentals of Immunology

effects. Dosage effect is sometimes used when preparing reagent RBCs for testing.

Effect of pH The ideal pH of a test system for antigen-antibody reactions ranges between 6.5 and 7.5, which is similar to the pH of normal plasma or serum. Exceptions include some anti-M and some Pr(Sp1) group antibodies that show stronger reactivity below pH 6.5.13 Acidification of the test serum may aid in distinguishing anti-M and anti-Pr(Sp1) antibodies from other antibodies.

Temperature Different isotypes of antibodies may exhibit optimal reactivity at different temperatures. IgM antibodies usually react optimally at ambient temperatures or below 22°C at the immediate spin (IS) phase of testing, whereas IgG antibodies usually require 37°C incubation and react optimally at the antihuman globulin (AHG) phase of testing. Because clinically significant antibodies may be in both these temperature ranges, it is important to do testing with a range of temperatures (Fig. 3–9).

Immunoglobulin Type Examples of IgM antibodies that have importance in blood banking include those against the ABH, Ii, MN, Lewis (Lea, Leb), Lutheran (Lua), and P blood group antigens. Important IgG antibodies are those directed against Ss, Kell (Kk, Jsa, Jsb, Kpa, Kpb), Rh (DCEce), Lutheran (Lub), Duffy (Fya, Fyb), and Kidd (Jka, Jkb) antigens (see Fig. 3–8). IgM antibodies are generally capable of agglutinating RBCs suspended in a 0.85% to 0.90% saline medium. The IgM antibody is 160 Å larger than an IgG molecule and approximately 750 times as

Types of Antibodies Reaction Phases

Immediate Spin Phase

IgM

Antiglobulin Phase (37ºC)

IgG

Figure 3–9. Types of antibodies and reaction phases. (From Kutt, SM, Larison, PJ, and Kessler, LA: Solving Antibody Problems, Special Techniques. Ortho Diagnostic Systems, Raritan, NJ, 1992, p 10, with permission.)

67

efficient as IgG in agglutination reactions. This allows it to easily bridge the distance between two RBCs.13 Another factor that contributes to the difference in reactivity between the IgM and IgG molecules is the number of antigen-combining sites on each type of immunoglobulin. The IgM molecule has the potential to bind 10 separate antigen sites; however, an IgG molecule has only 2 binding sites per molecule, which implies that an IgG molecule would have to bind 2 RBCs with only 1 binding site on each cell.13 IgM molecules rarely bind 10 sites, owing to the size and spacing of antigens in relation to the size and configuration of the IgM molecule. Typically, when the IgM molecule attaches to two RBCs, probably 2 or 3 antigen-combining sites attach to each RBC. Agglutination reactions involve more than one immunoglobulin molecule, and these conditions are multiplied many times in order to represent the agglutination reaction. Because of the basic differences in the nature of reactivity between IgM and IgG antibodies, different serologic systems must be used to optimally detect both classes of clinically significant antibodies. An overview of the serologic methods traditionally used for antibody detection in the blood bank laboratory is outlined in Table 3–8.

Enhancement Media Agglutination reactions for IgM antibodies and their corresponding RBC antigens are easily accomplished in saline medium, as these antibodies usually do not need enhancement or modifications to react strongly with antigens. However, detection of IgM antibodies may not have the same clinical significance as the detection of most IgG antibodies, because IgG antibodies react best at 37°C and are generally responsible for hemolytic transfusion reactions and HDN. To discover the presence of IgG antibodies, there are many enhancement techniques or potentiators available (Table 3–9). One of the key ways to enhance the detection of IgG antibodies is to increase their reactivity. Many of the commercially available enhancement media accomplish this by reducing the zeta potential of RBC membranes. The net negative charge surrounding RBCs (and most other human cells) in a cationic media is part of the force that repels RBCs from each other and is due to sialic acid molecules on the surface of RBCs. Most acids have a negative charge, and the large concentration of these molecules on RBCs creates a “zone” of negative charge around the RBC. This zone is protective and keeps RBCs from adhering to each other in the peripheral blood. A potential is created because of the ionic cloud of cations (positively charged ions) that are attracted to the zone of negative charges on the RBC membrane (Fig. 3–10).13 This potential around the RBC is called the zeta potential and is an expression of the difference in electrostatic charges at the RBC surface and the surrounding cations. IgM and IgG antibodies have differences in how they react to the same zeta potential. Reducing the zeta potential allows the more positively charged antibodies to get closer to the negatively charged RBCs and therefore increases RBC agglutination by IgG molecules.

2682_Ch03_045-076 28/05/12 2:32 PM Page 68

68

PART I

Fundamental Concepts

Table 3–8 Serologic Systems Used in Traditional Laboratory Methods for Red Cell Antibody Detection

REACTION PHASE

Ig CLASS COMMONLY DETECTED

PURPOSE AND MECHANISM OF REACTION

TESTS THAT USE SEROLOGIC SYSTEM

TYPE OF ANTIBODIES COMMONLY DETECTED

Immediate spin

IgM

IgM antibodies react best at cold temperatures.

ABO reverse testing

Expected ABO alloantibodies

IgM is an agglutinating antibody that has the ability to easily bridge the distance between red cells.

Cross-match

Unexpected cold-reacting alloantibodies or autoantibodies

IgG antibodies react best at warm temperatures.

Antibody screening/identification

37°C incubation

IgG

Autocontrol Antibody screening/identification No visible agglutination commonly seen.

Cross-match (if needed)

IgG is sensitizing antibody with fewer antigen binding sites than IgM and cannot undergo the second stage of agglutination, lattice formation.

Autocontrol

Complement may be bound during reactivity, which may or may not result in visible hemolysis. Antiglobulin test

IgG

Antihuman globulin (AHG) has specificity for the FC portion of the heavy chain of the human IgG molecule or complement components.

Antibody screening/identification

Unexpected warm-reacting alloantibodies or autoantibodies

Cross-match (if needed) Autocontrol AHG acts as a bridge cross-linking red cells sensitized with IgG antibody or complement.

Protein Media Colloidal substances, or colloids, are a type of clear solution that contains particles permanently suspended in solution. Colloidal particles are usually large moieties like proteins as compared with the more familiar crystalloids, which usually have small, highly soluble molecules, such as glucose, that are easily dialyzed. The colloidal solutes can be charged or neutral and go into solution because of their microscopic size. There are several colloidal solutions currently utilized in blood bank testing, and they are all used to enhance agglutination reactions. Colloids include albumin, polyethylene

Direct antiglobulin test (DAT)

glycol (PEG), polybrene, polyvinylpyrrolidone (PVP), and protamine. These substances work by increasing the dielectric constant (a measure of electrical conductivity), which then reduces the zeta potential of the RBC.

Low Ionic Strength Solution Media Low ionic strength solutions (LISS), or low salt media, generally contain 0.2% sodium chloride. They decrease the ionic strength of a reaction medium, which reduces the zeta potential and therefore allows antibodies to react more efficiently with RBC membrane antigens. LISS media are

2682_Ch03_045-076 28/05/12 2:32 PM Page 69

Chapter 3 Fundamentals of Immunology

69

Table 3–9 Potentiators REAGENT

ACTION

PROCEDURE

TYPE OF ANTIBODY ID Primarily IgM; IgG if incubated at 37°C

AHG

Cross-links sensitized cells, resulting in visible agglutination

1. DAT: AHG added directly to washed RBCs 2. IAT: serum + screen cells; incubation at 37°C for time determined by additive used; cell washing before addition of AHG

1. Polyspecific; anti-IgG + anticomplement

2. IgG monospecific: anti-IgG only

22% albumin*

Causes agglutination by adjusting zeta potential between RBCs

Incubation at 37°C for 15–60 min; cell washing prior to indirect antiglobulin test (IAT)

IgG

LISS*

Low ionic strength environment causes RBCs to take up antibody more rapidly

Incubation at 37°C for 5–15 min; cell washing before IAT

IgG

PEG*

Increases test sensitivity;

Incubation at 37°C for 10–30 min; cell washing before IAT

IgG

aggregates RBCs causing closer proximity of RBCs to one another, assisting in antibody cross-linking

NOTE: The test mixture cannot be centrifuged and examined reliably for direct agglutination after 37°C incubation.

Reduces RBC surface charge; destroys or depresses some RBC antigens; enhances other RBC antigens

1. One step: enzymes added directly to serum/RBC mixture 2. Two step: RBC pretreated with enzymes before addition of serum

Enzymes

Destroys Fya, Fyb, MNS; enhances reactivity to Rh, Kidd, P1, Lewis, and I antibodies

*All additives should be added after the IS phase immediately before 37°C incubation LISS = low ionic strength solutions; PEG = polyethylene glycol

often used because they result in an increased rate of antibody uptake during sensitization and a decreased reaction incubation time (from 30 to 60 minutes to 5 to 15 minutes as compared with protein potentiators such as albumin).13,14 However, they can result in false-positive reactions and may require testing to be repeated with albumin.

Polyethylene Glycol and Polybrene Advanced Concepts PEG and polybrene are macromolecule additives used with LISS to bring sensitized RBCs closer to each other to facilitate antibody cross-linking and agglutination reactions. They are often used in place of albumin and have some advantages and possible drawbacks. Polybrene can detect ABO incompatibility and clinically significant IgG

alloantibodies, whereas PEG produces very specific reactions with reduction in false-positive or nonspecific reactions. PEG is considered to be more effective than albumin, LISS, or polybrene for detection of weak antibodies. These reagents have been used in automated and manual testing systems.

Proteolytic Enzymes Enzymes are protein molecules that function by altering reaction conditions and bringing about changes in other molecules without being changed themselves. Only a small part of a large enzyme molecule reacts with a small part of another molecule, called its substrate. They are specific for the molecules they target and can modify proteins, nucleic acids, carbohydrates, or lipids. Proteolytic enzymes target protein molecules. Certain enzymes have been found to modify various blood group antigens and are useful in testing,

2682_Ch03_045-076 28/05/12 2:32 PM Page 70

70

PART I

Fundamental Concepts No Agglutination

Erythrocyte

Ionic Cloud IgG 14 nm

25 nm

35 nm

IgM Agglutination

especially in cases in which there are multiple antibodies present in a sample. Enzymes used in the detection and identification of blood group antibodies include ficin (isolated from fig plants), papain (from papaya), trypsin (from pig stomach), and bromelin (from pineapple). It is thought that treating RBCs with enzymes results in the release of sialic acid from the membrane with a subsequent decrease in the negative charges and zeta potential of the RBCs. It has also been suggested that enzyme treatment removes hydrophilic glycoproteins from the membrane of RBCs, causing the membrane to become more hydrophobic, which would allow RBCs to come closer together. Also, because of the removal of glycoproteins from the membrane, antibody molecules may no longer be subject to steric hindrance from reacting with RBC antigens. The use of enzymes provides enhanced antibody reactivity to Rh, Kidd, P1, Lewis, and I antigens and destroys or decreases reactivity to Fya, Fyb, M, N, and S antigens.14

Antihuman Globulin Reagents Basic Concepts When RBCs become coated with antibody or complement or both but do not agglutinate in regular testing, special reagents are needed to produce agglutination. The direct antihuman globulin (AHG) test is designed to determine if RBCs are coated with antibody or complement or both. Polyspecific AHG can determine if RBCs have been sensitized with IgG antibody or complement (components C3b or C3d) or both. Monospecific AHG reagents react only with RBCs sensitized with IgG or complement.14 Refer to Chapter 5, “The Antiglobulin Test.”

Figure 3–10. Schematic representation of the ionic cloud concept and its relevance to hemagglutination induced by IgM and IgG antibodies. Compare the size of the IgG antibody with that of the IgM molecule. The size of the IgG molecule is not large enough to span the distance between two adjacent RBCs.

Blood bank reagents can be either polyclonal or monoclonal in source. In the indirect antiglobulin test, the same AHG reagents are used to detect antibodies or complement that have attached to RBC membranes but with a prior incubation step with serum (or plasma). If the antibodies present in serum cannot cause RBC agglutination but only sensitize the RBCs, then the AHG reagents will allow for agglutination to occur by cross-linking the antibodies on the RBCs. The use of AHG reagents allows blood bank testing to be more sensitive. AHG is one of the most important reagents, and the development of AHG is one of the milestones in blood bank testing (see Tables 3–8 and 3–9).

Chemical Reduction of IgG and IgM Molecules Advanced Concepts There are special reagents available that can be used to help identify the different antibodies present in a mixture of alloantibodies or alloantibodies occurring with autoantibodies. The reagents generally act on covalent sulfhydryl bonds and facilitate antibody identification by removal of either IgG or IgM antibodies. Dithiothreitol (DTT) and ␤-2mercaptoethanol (2-ME) are thiol-reducing agents that break the disulfide bonds of the J (joining) chain of the IgM molecule but leave the IgG molecule intact.10 Another reagent, ZZAP, which consists of a thiol reagent plus a proteolytic enzyme, causes the dissociation of IgG molecules from the surface of sensitized RBCs and alters the surface antigens of the RBC.2 Chemical reduction of the disulfide bond of the IgG molecule is also used to produce chemically modified reagents that react with RBCs in saline. Sulfhydryl compounds reduce the strong but less flexible covalent

2682_Ch03_045-076 28/05/12 2:32 PM Page 71

Chapter 3 Fundamentals of Immunology

disulfide bonds in the hinge region of the IgG molecule, allowing the Fab portions more flexibility in facilitating agglutination reactions.13

Monoclonal Versus Polyclonal Reagents Basic Concepts Traditional polyclonal antisera reagents have been produced by immunizing donors with small amounts of RBCs positive for an antigen that they lack and then collecting the serum and isolating antibodies against that antigen. AHG reagents were originally made by injecting animals (usually rabbits) with human globulin components and then collecting the antihuman antibodies. One antigen can have a number of different epitopes, and polyclonal reagents are directed against multiple epitopes found on the original antigen used to stimulate antibody production. (Refer to Chapter 5.) Monoclonal reagents are directed against specific epitopes and therefore are a potential solution. They are made by hybridoma technology with spleen lymphocytes from immunized mice that are fused with rapidly proliferating myeloma cells. The spleen lymphocytes have single epitope specificity; the myeloma cells (a type of immortalized, cultured cell) make vast amounts of antibody. After extensive screening and testing, these very efficient hybrid cells are selected and cultured to produce lines of immortal cell clones that make a lot of one type of antibody that reacts with one specific epitope. Monoclonal reagents do not use human donors and therefore do not use a human source for reagent purposes. Monoclonal reagents have several important advantages over polyclonal reagents. Because monoclonal reagents are produced from immortal clones maintained in vitro, no batch variation exists, and nearly unlimited high titers of antibodies can be produced. Also, the immortal clones can be kept growing in in vitro culture for years without loss of production and are therefore cost-efficient. Monoclonal antibodies react very specifically and often have higher affinities. For these reasons, monoclonal reagents are not subject to cross-reactivity and interference from nonspecific reactions, and they can react strongly with the small quantities of antigen in some antigen subgroups; therefore, AHG phase testing may not be needed. Unfortunately, there are some disadvantages of monoclonal antisera use, such as overspecificity. The fact that complement may not be fixed in the antigen-antibody reaction may cause false-negative results; problems with oversensitivity may cause false-positive results. Some of the disadvantages of monoclonal reagents may be overcome by using blends of different monoclonal reagents or by using polyclonal reagents and monoclonal reagents together.2 Monoclonal antisera have generally replaced most of the polyclonal antisera and have been used for HLA typing, AHG testing, and RBC and lymphocyte phenotyping.

71

Nontraditional Laboratory Methods Advanced Concepts Sophisticated testing methods used in immunology research laboratories have become more commonplace in transfusion laboratories. These technologies are discussed in more detail in Chapter 12, “Other Technologies and Automation.” Flow Cytometry Some of the most important techniques to study immunologic reactions and systems are fluorescence-assisted cell sorting (FACS) and flow cytometry. Flow cytometry makes use of antibodies that are tagged with a fluorescent dye. Fluorescence occurs when the compound absorbs light energy of one wavelength and emits light of a different wavelength. Cells that are coated with fluorescent-labeled antibody emit a brightly fluorescent color of a specific wavelength. Fluorescent dyes are used as markers in immunologic reactions, and a fluorochrome-labeled antibody can be visualized by an instrument that detects emitted light. There are many different fluorochromes available that have various colors, and they can be coupled to nearly any antibody with minimal problems with spectral overlap. Flow cytometry can be used to obtain quantitative and qualitative data on cell populations and to sort different cell populations. There are direct and indirect procedures for labeling with fluorochromes. In a direct procedure, the specific antibody, called the primary antibody, is directly conjugated with a fluorescent dye and reacts with a specific antigen. Indirect procedures need a secondary antibody that is conjugated to a fluorochrome that reacts with an unlabeled specific primary antibody that has reacted with antigen. Indirect methods often require more complex analysis because these reactions have higher amounts of nonspecificity. The secondary antibody is usually made against the species of the primary antibody. The principle of flow cytometry is based on the scattering of light as cells are bathed in a fluid stream through which a laser beam enters. The cells move into a chamber one at a time and absorb light from the laser. If labeled antibody is bound to the cell, then the light emitted is different from light emitted by cells without antibody. The flow cytometer instrument makes the distinction between different wavelengths of light. The light signal is amplified and analyzed. There are a number of components to the flow cytometry system that include: one or more lasers for cell illumination, photodetectors for signal detection, a possible cell sorting device, and a computer to manage the data.15 Fluorescence is used in place of hemagglutination as the endpoint of the reaction. Immunofluorescent antibodies and flow cytometry have been used to quantify fetomaternal hemorrhage, identify transfused cells and follow their survival in recipients, measure low levels of cell-bound IgG, and distinguish homozygous from heterozygous expression of blood group antigens.2

2682_Ch03_045-076 28/05/12 2:32 PM Page 72

72

PART I

Fundamental Concepts

Diseases Important in Blood Bank Serologic Testing Advanced Concepts A number of diseases that are immune-mediated are important in blood bank testing and merit a brief mention here. For further detail, please refer to the appropriate chapter in this textbook. However, some of these will be discussed within the context of this chapter to emphasize their importance in blood testing. Immunodeficiency Immunodeficiency diseases can result from various defects at many different levels of immune function and may be congenital or acquired. They can result from defects in either innate or adaptive immunity or both; the cause is often not known. Some of the more well-known immunodeficiencies are listed in Box 3–4.16 Immunodeficiencies can influence blood bank test results and transfusion decisions, such as when there is a false-negative reverse grouping for ABO due to low immunoglobulin levels.

Hypersensitivity Hypersensitivity (or allergy) is an inflammatory response to a foreign antigen and can be cell- or antibody-mediated or both. There are four different types of hypersensitive reactions, and the symptoms and treatment required for each are different. All four types can be caused by blood product transfusions and may be the first sign of a transfusion reaction. Type I reaction, also called anaphylaxis or immediate hypersensitivity, involves histamine release by mast cells or basophils with surface IgE antibody. It can occur in IgA-deficient individuals who receive plasma products containing IgA. Urticarial reactions (skin rashes) may also result from transfusion of certain food allergens or drugs in plasma products. A type II reaction can involve IgG or IgM antibody with complement, phagocytes, and proteolytic enzymes. HDN or transfusion reactions caused by blood group antibodies and autoimmune hemolytic reactions are all type II reactions. Like type II reactions, type III reactions involve phagocytes and IgG and IgM and complement. Type III reactions result in tissue damage from the formation of immune complexes of antigen-antibody aggregates, complement, and phagocytes and are therefore very serious. Penicillin and

BOX 3–4

Classification of Immunodeficiency Disorders Antibody (B Cell) Immunodeficiency Disorders • X-linked hypogammaglobulinemia (congenital hypogammaglobulinemia) • Transient hypogammaglobulinemia of infancy • Common, variable, unclassifiable immunodeficiency (acquired by hypogammaglobulinemia) • Immunodeficiency with hyper-IgM • Selective IgA deficiency • Selective IgM deficiency • Selective deficiency of IgG subclasses • Secondary B-cell immunodeficiency associated with drugs, protein-losing states • X-linked lymphoproliferative disease Cellular (T Cell) Immunodeficiency Disorders • Congenital thymic aplasia (DiGeorge syndrome) • Chronic mucocutaneous candidiasis (with or without endocrinopathy) • T-cell deficiency associated with purine nucleoside phosphorylase deficiency • T-cell deficiency associated with absent membrane glycoprotein • T-cell deficiency associated with absent class I or II MHC antigens or both (base lymphocyte syndrome)

• Cellular immunodeficiency with abnormal immunoglobulin synthesis (Nezelof syndrome) • Immunodeficiency with ataxia-telangiectasia • Immunodeficiency with eczema and thrombocytopenia (Wiskott-Aldrich syndrome) • Immunodeficiency with thymoma • Immunodeficiency with short-limbed dwarfism • Immunodeficiency with adenosine deaminase deficiency • Immunodeficiency with nucleoside phosphorylase deficiency • Biotin-dependent multiple carboxylase deficiency • Graft-versus-host disease • Acquired immunodeficiency syndrome (AIDS) Phagocytic Dysfunction • • • • • • • •

Chronic granulomatous disease Glucose-6-phosphate dehydrogenase deficiency Myeloperoxidase deficiency Chediak-Higashi syndrome Job’s syndrome Tuftsin deficiency Lazy leukocyte syndrome Elevated IgE, defective chemotaxis, and recurrent infections

Combined Antibody-Mediated (B Cell) and Cell-Mediated (T Cell) Immunodeficiency Disorders • Severe combined immunodeficiency disease (autosomal recessive, X-linked, sporadic) Ammann, AJ: Mechanisms of immunodeficiency. In Stites, DP, Terr, AI, and Parslow, TG (eds): Basic and Clinical Immunology, 8th ed. Appleton & Lange, Norwalk, 1994, with permission.

2682_Ch03_045-076 28/05/12 2:32 PM Page 73

Chapter 3 Fundamentals of Immunology

other drug-induced antibodies can lead to hemolytic reactions through type III hypersensitivity. The type IV reaction involves only T cell–mediated responses and their cytokines and can be fatal if untreated. The most important type IV reaction is graft-versus-host, of which there is also more than one type. Immunocompromised and immunosuppressed patients must receive irradiated blood products so that T lymphocytes do not engraft and attack the host tissues. Type IV reactions are a problem for bone marrow transplant and stem cell transfusion recipients. (Refer to Chapter 16, “Adverse Effects of Blood Transfusion.”)

Monoclonal and Polyclonal Gammopathies Plasma cell neoplasms result in proliferation of abnormal immunoglobulin from either a single B-cell clone (monoclonal gammopathies) or multiple clones (in polyclonal gammopathies) and may be a specific isotype or only light or heavy chain molecules. Increased serum viscosity is a result of these diseases and can interfere with testing. The increased concentrations of serum proteins can cause nonspecific aggregation (as opposed to agglutination) of erythrocytes called rouleaux, which is seen as a stacking of RBCs. It often occurs in multiple-myeloma patients. If rouleaux is suspected, saline replacement technique may be needed to distinguish true cell agglutination from nonspecific aggregation. Roleaux primarily causes problems in the ABO reverse grouping, antibody screening, and compatibility testing procedures. However, excess immunoglobulin coating red cells can cause spontaneous aggregation to occur also.

Autoimmune Disease Autoantibodies are produced against the host’s own cells and tissues. It is unknown why this loss of tolerance to selfantigens occurs, but there are many possible explanations such as aberrant antigen presentation, failure to obtain clonal deletion, anti-idiotypic network breakdown, and cross-reactivity between self and nonself antigens. Autoimmune hemolytic anemias are an important problem in testing and transfusion. They may produce antibodies that cause RBC destruction and anemia and result in antibody- or complementsensitized RBCs. The direct antiglobulin test should be done to detect sensitized RBCs and determine if the cells are coated with antibody or complement. Special procedures such as elution or chemical treatment to remove antibody from cells may be required to prepare RBCs for antigen typing. Serum autoantibodies may interfere with testing for clinically significant alloantibodies. Special reagents and procedures to denature immunoglobulins may be required to remove autoantibodies from serum so they do not interfere with the testing. (Refer to Chapter 20, “Autoimmune Hemolytic Anemias.”)

Hemolytic Disease of the Newborn Hemolytic disease of the fetus and newborn (HDFN) can result when the maternal IS produces an antibody directed

73

at an antigen present on fetal cells but absent from maternal cells. The mother is exposed to fetal RBCs as a result of fetomaternal transfer of cells during pregnancy or childbirth. Maternal memory cells can cause a stronger response during a second pregnancy if the fetus is positive for the sensitizing antigens. IgG1, IgG3, and IgG4 are capable of crossing the placenta and attaching to fetal RBCs, whereas IgG2 and IgM are not. Severe HDFN is most often associated with IgG1 antibodies and may require exchange transfusion. Antigens of the ABO, Rh, and other blood group systems such as Kell have been shown to cause HDFN. (Refer to Chapter 19, “Hemolytic Disease of the Fetus and Newborn [HDFN].”)

Blood Product Transfusions and the Immune System The immune system may undergo transient depression following the administration of blood and blood products. This is referred to as transfusion-related immunomodulation (TRIM). With a weakened immune system, there is an increased risk of an individual developing infections or cancer. The exact mechanism(s) causing TRIM are not known and have not been fully elucidated, but three major mechanisms seem to have emerged: clonal deletion, induction of anergy, and immune suppression. In clonal deletion, alloreactive lymphocytes are inactivated and removed, thus preventing a potential graft rejection (as in kidney organ). With induction of anergy, there is an unresponsiveness of the immune system most likely due to a failure of T cells to respond. In immune suppression, responding cells appear to be inhibited by some sort of cellular mechanism or cytokine. Immune suppression can be due to a number of factors. Certain cytokines, including interleukins and some growth factors, can decrease immune responsiveness. Suppression of some IS components is critical at certain times, so the IS does not become overactivated and attack host cells. T and B cells that recognize host cells and might destroy them must be removed before they can develop into mature lymphocytes. Specific suppressor cells have recently been isolated. They have unique CD profiles and play a role in modulating lymphocyte function. Immune suppression can also occur when there is too little immunoglobulin made or when too many T and B cells are lost through severe infection, extreme immune stimulation, or IS organ failure. It is believed that some constituents of cellular blood products may be responsible for TRIM. These constituents include allogeneic mononuclear cells, chemicals released by allogenic mononuclear cells as they age, and soluble HLA peptides I that circulate in plasma. Any decision to transfuse blood products must be approached with caution. Obviously, the best way to avoid TRIM is not to transfuse at all. If transfusion is required, the patient’s immune status must be taken into consideration. The use of leukoreduction filters may help to reduce the risk for TRIM. (Refer to Chapter 15, “Transfusion Therapy.”)

2682_Ch03_045-076 28/05/12 2:32 PM Page 74

74

PART I

Fundamental Concepts

SUMMARY CHART

 

   

 

The immune system interacts with other host systems and maintains the host equilibrium. The two major roles for the IS are: • Protection from pathogens and foreign substances • Removal of abnormal and damaged host cells The two major branches of the IS are: • Innate, or natural—the nonspecific primitive IS • Acquired, or adaptive—the specific, evolved IS The two major arms of the acquired IS are: • Humoral, mediated by B cells and antibody production • Cellular, mediated by T cells and lymphokines The basic mechanisms used by the IS are: • Recognition of self and nonself organisms, cells, and tissues • Removal of unwanted organisms, cells, and tissues (self or nonself) • Repair of damaged host tissues The acquired IS demonstrates diversity and uniqueness: • Individual B and T cells have vast arrays of unique membrane molecules that can have configurations to match nearly any antigen in the environment. • Each individual lymphocyte has one unique receptor per cell that recognizes one epitope. • Antibodies and T-cell receptors recognize and react only with the antigen that matches and fits their specific configuration. • Selected T and B cells can remain dormant and later respond more rigorously upon second exposure of a previously recognized antigen. The acquired IS demonstrates tolerance: this indicates that immune responses against the host are either removed or downregulated. There are three types of lymphocytes: T cells, B cells, and NK cells. T cells (or lymphocytes) have the TCR, which is usually associated with the CD3 complex, and T cells require APCs to respond to antigens. There are two well-characterized subpopulations of T cells distinguished by CD markers—T helper (TH, CD4-positive) and T cytotoxic (Tc, CD8-positive) lymphocytes. TH lymphocytes have CD4 markers on their cell membranes, provide B-cell help to stimulate the immune response, release lymphokines when stimulated, and recognize antigens in association with MHC class II molecules. TC lymphocytes have the CD8 marker on their membranes and can eliminate specific target cells without the help of antibody (cytotoxicity). B lymphocytes (or cells) make up about 5% to 15% of circulating lymphocytes and are characterized by their membrane-bound antibodies (or immunoglobulins)

 

 

Membrane-bound antibodies are manufactured by B cells and inserted into their cell membranes, where they act as antigen receptors. Stimulated B cells differentiate into plasma cells to secrete humoral immunoglobulin; B cells receive T-cell help for antibody production and for immunologic memory; a single B cell clone manufactures Ig of a single specificity for a specific antigen for its entire cell lifetime. The primary, or original, immune response occurs after the first exposure to an antigen. The secondary, or anamnestic, immune response happens after a second exposure with the same specific antigen. Complement consists of a large group of different enzymatic proteins (convertases/esterases) that circulate in an inactive proenzyme form. Once the cascade is started, they activate each other in a sequence to form products that are involved in optimizing phagocytosis and cell lysis. Complement can be activated through three pathways: • The classical pathway is initiated by antigenantibody complexes and requires C1q for activation to proceed. • The alternative pathway is activated by certain macromolecules on the cell walls of bacteria, fungi, parasites, and tumor cells and requires C3b, serum factors B, D, properdin, and initiating factor. • The lectin pathway is activated by binding of MBL to microbes. All three pathways meet at a common point in the cascade and result in the formation of the membrane attack complex to remove unwanted cells. There are five classes (or isotypes) of immunoglobulins, all of which have a basic four-chain protein structure consisting of two identical light chains and two identical heavy chains. Disulfide (covalent) bonds link each light chain to a heavy chain and link the two heavy chains to each other. Antibody molecules are isotypic (based on heavy chain subtype), allotypic (based on one heavy chain mutation), or idiotypic (based on hypervariable and variable regions of light and heavy chains) and are reflected in the Ig sequences. Blood group antibodies may be characterized by such factors as epitope and variable region diversity (monoclonal or polyclonal), mode of sensitization (naturally occurring or immune), expected or unexpected presence in routine serum samples, isotype class (IgM, IgG, or, rarely, IgA), activity (warm or cold reactive or both, agglutinating or sensitizing), clinical significance, alloantibody or autoantibody specificity, serum titer, and chemical reactivity (influence of enzymes, sensitivity to pH, DTT, or 2-ME reagents).

2682_Ch03_045-076 28/05/12 2:32 PM Page 75

Chapter 3 Fundamentals of Immunology

Review Questions 1. Which of the following is not involved in the acquired or

adaptive immune response? Phagocytosis Production of antibody or complement Induction of immunologic memory Accelerated immune response upon subsequent exposure to antigen

a. b. c. d.

2. Which cells are involved in the production of antibodies? a. b. c. d.

Dendritic cells T lymphocytes B lymphocytes Macrophages

3. Which of the following cells is involved in antigen recog-

nition following phagocytosis? B lymphocytes T lymphocytes Macrophages Granulocytes

a. b. c. d.

4. The role of the macrophage during an antibody response

is to: Make antibody Lyse virus-infected target cells Activate cytotoxic T cells Process antigen and present it

a. b. c. d.

5. Which of the following immunoglobulins is produced in

the primary immune response? IgA IgE IgG IgM

a. b. c. d.

6. Which of the following immunoglobulins is produced in

the secondary immune response? IgA IgE IgG IgM

a. b. c. d.

7. Which of the following MHC classes are found on

antigen presenting cells? Class I Class II Class III Class IV

a. b. c. d.

8. Which of the following MHC classes encodes complement

components? Class I Class II Class III Class IV

a. b. c. d.

75

9. Which of the following immunoglobulins is most effi-

cient at binding complement? a. IgA b. IgE c. IgG d. IgM 10. Which portion of the immunoglobulin molecules

contains complement binding sites? a. Heavy chain variable region b. Light chain variable region c. Heavy chain constant region d. Light chain constant region 11. Which complement pathway is activated by the forma-

tion of antigen-antibody complexes? a. Classical b. Alternative c. Lectin d. Retro 12. Which of the following is known as the “recognition

unit” in the classical complement pathway? a. C1q b. C3a c. C4 d. C5 13. Which of the following is known as the “membrane

attack complex” in the classical complement pathway? a. C1 b. C3 c. C4, C2, C3 d. C5b, C6, C7, C8, C9 14. Which of the following immunoglobulin classes is

capable of crossing the placenta and causing hemolytic disease of the newborn? a. IgA b. IgE c. IgG d. IgM 15. Which of the following refers to the effect of an excess

amount of antigen present in a test system? a. Postzone b. Prozone c. Zone of equivalence d. Endzone 16. Which of the following refers to the presence of an

excess amount of antibody present in a test system? a. Postzone b. Prozone c. Zone of equivalence d. Endzone

2682_Ch03_045-076 28/05/12 2:32 PM Page 76

76

PART I

Fundamental Concepts

17. Which of the following refers to a state of equilibrium

in antigen-antibody reactions? a. Postzone b. Prozone c. Zone of equivalence d. Endzone 18. Which one of the following properties of antibodies is

NOT dependent on the structure of the heavy chain constant region? a. Ability to cross the placenta b. Isotype (class) c. Ability to fix complement d. Affinity for antigen 19. Molecules that promote the update of bacteria for

phagocytosis are: a. Opsonins b. Cytokines c. Haptens d. Isotypes 20. Select the term that describes the unique confirmation

of the antigen that allows recognition by a corresponding antibody: a. Immunogen b. Epitope c. Avidity d. Clone 21. Which of the following terms refers to the net negative

charge surrounding red blood cells? a. Dielectric constant b. Van der Waals forces c. Hydrogen bonding d. Zeta potential

References 1. Waytes, AT, et al: Pre-ligation of CR1 enhances IgG-dependent phagocytosis by cultured human monocytes. J Immunol 146:2694, 1991. 2. Roback, J, Combs, M, Grossman, B, and Hillyer, C: Technical Manual, 16th ed. CD-ROM. American Association of Blood Banks, Bethesda, MD, 2009.

3. Sunshine, G, and Coico, R: Immunology: A Short Course, 6th ed. John Wiley & Sons, Hoboken, 2009. 4. Stites, DP, Parslow, TG, Imboden, JB, and Terr, AI (eds): Medical Immunology, 10th ed. McGraw-Hill, New York, 2001. 5. Nance, SJ, Arndt, PA, and Garratty, G: Correlation of IgG subclass with the severity of hemolytic disease of the newborn. Transfusion 30:381, 1990. 6. Rieben, R, et al: Antibodies to histo-blood group substances A and B: Agglutination titers, Ig class, and IgG subclasses in healthy persons of different age categories. Transfusion 31:607, 1991. 7. Sokol, RJ, et al: Red cell autoantibodies, multiple immunoglobulin classes, and autoimmune hemolysis. Transfusion 30:714, 1990. 8. Kerr, WG, Hendershot, LM, and Burrows, PD: Regulation of IgM and IgD expression in human B-lineage cells. J Immunol 146:3314, 1991. 9. Klein, HG, and Anstee, DJ (eds): Red cell antibodies against self-antigens, bound antigens and induced antigens. In Mollison’s Blood Transfusion in Clinical Medicine, 11th ed. WileyBlackwell, Oxford, UK, 2007, pp 253–298. 10. Klein, HG, and Anstee, DJ (eds): ABO, Lewis and P groups and Ii antigens. In Mollison’s Blood Transfusion in Clinical Medicine, 11th ed. Wiley-Blackwell, Oxford, UK, 2007, pp 114–162. 11. Turgeon, ML: Fundamentals of Immunohematology, 2nd ed. Lippincott Williams & Wilkins, Philadelphia, 2003. 12. Schleuning, M, et al: Complement activation during storage of blood under normal blood bank conditions: Effects of proteinase inhibitors and leukocyte depletion. Blood 79:3071, 1992. 13. Issitt, PD, and Anstee, DJ: Applied Blood Group Serology, 4th ed. Montgomery Scientific, Durham, NC, 1998, pp 34–35. 14. Kutt, SM, et al: Rh Blood Group System Antigens, Antibodies, Nomenclature, and Testing. Ortho Diagnostic Systems, Raritan, NJ, 1990, pp 13–14. 15. Stevens, CD: Clinical Immunology and Serology: A Laboratory Perspective, 3rd ed. FA Davis Company, Philadelphia, 2009. 16. Ammann, AJ: Mechanisms of immunodeficiency. In Stites, DP, Terr, AI, and Parslow, TG (eds): Basic and Clinical Immunology, 8th ed. Appleton & Lange, Norwalk, 1994.

2682_Ch04_077-100 22/05/12 11:40 AM Page 77

Chapter

4

Concepts in Molecular Biology Maria P. Bettinotti, PhD, dip. ABHI; Lorraine Caruccio, PhD, MT(ASCP)SBB; and Barbara Kraj, MS, MLS(ASCP)CM

Introduction DNA Is the Genetic Material Features Relevant to Molecular Techniques Expression of Genetic Information The Central Dogma of Molecular Biology, Expanded Recombinant DNA The Coding Sequence of a Gene Tools for DNA Cloning Expression of Cloned Genes: Recombinant Proteins in Clinical Use The Polymerase Chain Reaction

DNA Sequencing Detection of Nucleic Acids and Proteins Nucleic Acid Hybridization PCR-Based and Other Amplification Techniques Antibodies as Probes for Proteins Techniques for Studying Gene Polymorphism Restriction Fragment Length Polymorphism PCR and Allele-Specific Probes DNA Sequencing DNA Profiling or “Fingerprinting”

Systems Biology Red Cell Genotyping Genetic Basis of Blood Groups Molecular Basis of Blood Group Polymorphism Clinical Applications of Red Cell Genotyping Summary Chart Review Questions References

OBJECTIVES 1. Refer to the contributions by Griffith, Avery, Hershey, and Chase, and explain how DNA was proven to be the carrier of genetic information. 2. Explain the significance of Chargaff’s rules and x-ray diffraction studies by Wilkins and Franklin in Watson and Crick’s discovery of the DNA double helix structure. 3. Describe DNA features fundamental in the design of molecular assays and define the applicable terms: complementarity, hydrogen bonding, melting point, denaturation, annealing, and polarity. 4. Explain what the central dogma of molecular biology is and how it expanded after the discovery of reverse transcriptase enzyme. 5. Explain what the recombinant DNA technology is and describe the tools used in molecular cloning: restriction endonucleases, vectors, and host cells. 6. Define gene expression and explain how it may be studied and used in manufacturing of recombinant proteins. 7. Summarize the procedures of plasmid DNA isolation and gel electrophoresis. 8. Explain the principles of the polymerase chain reaction as an in vitro molecular procedure mimicking the process of semiconservative DNA replication occurring in vivo. 9. Discuss the differences between classic PCR, reverse-transcriptase, and real-time PCR. 10. Describe the principle of transcription-mediated amplification. 11. Describe Sanger’s sequencing dideoxy chain termination method. 12. Recognize the differences between immunoblotting and hybridization methods: Southern and Northern analysis, microarrays, and fluorescent in situ hybridization. 13. Explain major principles of methods used in studying gene polymorphisms: RFLP, VNTR, SSP, and SSOP. 14. Explain how nucleic acid testing (NAT) in donor blood improves the process of screening for infectious disease. 15. Describe the applications of RBC molecular antigen typing. 77

2682_Ch04_077-100 22/05/12 11:40 AM Page 78

78

PART I

Fundamental Concepts

Introduction Molecular biology is the science that studies the molecular interactions that take place in the living cell. For the molecular biologist, the master molecules are the nucleic acids: the deoxyribonucleic acid (DNA) and the ribonucleic acid (RNA). According to the original central dogma of molecular biology, the basic information of life flows from DNA through RNA to proteins.1 By means of the genetic code, a sequence of nucleotides within a gene is transcribed and translated into a sequence of amino acids that form a peptide or protein. The processes of transcription and translation (reviewed in Chapter 2, “Basic Genetics”) are referred to as gene expression. The key to the chemistry of life is the variety of gene expression products that are unique structural or functional protein molecules. A protein may be shaped into a building component of a cell. For example, spectrin is a main structural protein of the red blood cell (RBC) skeleton. Defects in the spectrin gene lead to hereditary spherocytosis (HS), a condition characterized by fragile, spherical RBCs, which the spleen traps and destroys. A protein may temporarily bind particular substrate molecules, enabling these molecules to chemically react with each other. Proteins that act as catalysts of these chemical reactions are called enzymes. A good example is the ABO blood group system. The H gene codes for protein fucosyl transferase, an enzyme that adds sugar L-fucose to a series of precursor structures. Once L-fucose has been added, the A and B gene–specified enzymes can add sugars to the chains that now carry the H residue. In other words, these genes determine a carbohydrate structure through the action of their encoded proteins acting as enzymes. (Refer to Chapter 6, “The ABO Blood Group System.”) Some proteins may be shaped to bind to DNA at specific nucleotide sequences in the chromatin to influence gene expression. These proteins act as transcription factors. Through all these mechanisms, the genotype of a cell is translated into its phenotype. Transfusion medicine is tied to three branches of molecular biology: (1) molecular genetics, because donor-recipient compatibility depends on the genetic transmission of polymorphic tissue markers, such as blood groups and human leukocyte antigens (HLA); (2) biotechnology, because of the production of recombinant proteins relevant to blood banking, such as growth factors, erythropoietin, and clotting factors; and (3) molecular diagnostics, because of the applications of molecular-based methods in the detection of transfusiontransmitted pathogens. Therefore, blood bankers must learn the basic principles of molecular biology. Chapter 2 describes in detail the biochemistry of gene replication, transcription, and translation. In this chapter, some of the experiments and concepts that led to the discovery and understanding of the mechanisms underlying these phenomena are reviewed. These experiments are direct predecessors of modern benchtop molecular techniques relevant to immunohematology. This chapter provides a brief introduction to molecular biology and supplements the description of molecular applications presented in other sections of

this book. Blood group genotyping, a relatively new and evolving application of molecular technology in transfusion medicine, is introduced at the end of this chapter.

DNA Is the Genetic Material Living organisms can replicate and pass hereditary traits (genes) to successive generations; this is their most distinctive characteristic. Refer to Chapter 2 for an in-depth review of Mendel’s laws and other concepts fundamental to heredity. In 1928, the British microbiologist Frederick Griffith presented a model system that was key to demonstrating that DNA was the material that carried the genetic information responsible for the features of living organisms (Fig. 4–1). He used two naturally occurring strains of Streptococcus pneumoniae bacterium that differed in their infectivity of mice.2 The virulent smooth (S) strain, which has a smooth polysaccharide capsule, kills mice through pneumonia. The nonvirulent rough (R) strain lacks the immunoprotective outer capsule and is nonlethal to mice because it is easily recognized and destroyed by the murine immune system. Injection of S-strain bacteria killed by heat does not cause any disease. However, simultaneous coinjection of the mixture of nonvirulent R strain with heat-killed S strain is lethal, and virulent S-strain bacteria can be recovered from mice infected with this mixture. Some heat-resistant component (a “transforming principle”) from the heat-killed S strain is able to transform the living R strain from innocuous to virulent (S). This experiment has been known as Griffith’s transformation. It is still the basis for transfer of genetic material from one organism to another in the laboratory setting. Griffith

1

2 R Strain

S Strain

Mouse Dies

3

Heat-killed S Strain

Mouse Lives

Mouse Lives

4

Heat-killed S Strain + Live R Strain

Mouse Dies Live S Strain isolated from mouse

Figure 4–1. Griffith’s transformation experiment. Bacterial cells can be transformed from nonpathogenic to virulent by heat-resistant component of the virulent strain: (1) Mice injected with encapsulated Streptococcus pneumoniae strain S die. The strain is virulent. (2) Mice injected with non-encapsulated Streptococcus pneumoniae strain R live. The strain is nonvirulent. (3) Mice injected with heat-killed S strain live. (4) Mice injected with a mixture of R live strain and heat-killed S strain die, and live S strain can be isolated from them.

2682_Ch04_077-100 22/05/12 11:40 AM Page 79

Chapter 4 Concepts in Molecular Biology

was lucky choosing this particular species to demonstrate the transformation, because many cell types are very resistant to this process, which is now facilitated by harsh conditions like use of chemicals (detergents), electricity (electroporation), or liposomes. But how do we know that this genetic transformation occurred due to transfer of DNA? Oswald T. Avery and his group at Rockefeller Institute were able to reproduce Griffith’s transformation in vitro. In 1944, they reported that they had purified the “transforming principle.”3 By molecular composition and weight, it was mainly DNA. Moreover, treatment with RNA or protein hydrolytic enzymes did not degrade it, but treatment with DNase caused loss of activity. Avery’s group’s conclusion that DNA was responsible for the transformation was not accepted immediately. Some in the scientific community suspected that inadequately destroyed proteins that contaminated the isolated DNA caused the transformation. In 1952, Alfred Hershey and Martha Chase reported an experiment that convinced the scientific community that genes are constituted by DNA (Fig. 4–2). They infected in parallel two bacterial cultures with phages (bacterial viruses), in which either the protein capsule was labeled with radioactive sulfur (35S) or the DNA core was labeled with radioactive phosphorus (32P). After dislodging the phage particles from the bacteria with a blender, they pelleted the bacteria by centrifugation. The phage particles were left in the supernatant. Following the centrifugation, 35S (protein) was only in the supernatant and 32P (DNA) was only in the pellet. From this pellet, a new generation of phages arose. The investigators concluded that the phage protein removed from the cells by stirring was the empty phage coat, whose mission was to transport the DNA from cell to cell. The DNA was the material of life, containing the phage genetic information necessary for the viral reproduction inside the bacteria.4

Features Relevant to Molecular Techniques In 1950, Erwin Chargaff of Columbia University reported results of DNA quantitative analysis that became known as Chargaff’s rules.5 Later, Maurice Wilkins and Rosalind Franklin produced x-ray diffraction photographs of DNA that suggested a helical structure. Based on these clues, in 1953, James Watson and Francis Crick published a seminal in which they proposed that the DNA molecule was a double α helix.6 DNA was a helical ladder, the rails of which were built from alternating units of deoxyribose and phosphate. Each rung of the ladder was composed of a pair of nitrogencontaining nucleotides (a base pair) held together by hydrogen bonds. The double helix consisted of two strands of nucleotides that ran in opposite directions (they were antiparallel), designated by polarity (directionality) labels 3’ and 5’, which refer to the number assigned by convention to the deoxyribose carbon atom linked to either the hydroxyl or phosphate group (see Chapter 2 and Fig. 2–10). The 3’ and 5’ ends determine the direction of DNA replication and transcription.

1

79

1 35

S Protein

2

32

P DNA

32

P DNA

2

35

3

S Protein

3

4

4 35

S Protein

32

P DNA

Figure 4–2. The Hershey-Chase phage experiment. DNA is the molecule that carries genetic information: (1) Bacteriophages were labeled with 35S or with 32P; 35S was incorporated into proteins and 32P into DNA. (2) Two Escherichia coli (E. coli) cultures were infected in parallel with the two different phages. (3) Phages were dislodged from bacteria by treatment with a blender. (4) After centrifugation, 35S (proteins) were detected only in the supernatant of the first culture and 32P (DNA) only in the pellet of the second culture. The phages remained in the supernatant and the bacteria in the pellet. From the bacterial pellet, a new generation of viruses could be raised.

Consistent with x-ray diffraction, about 10 base pairs were stacked on top of each other at each turn of a helix. Adenine always paired by two hydrogen bonds with thymine; guanine always paired by three hydrogen bonds with cytosine. Due to this complementarity resulting from formation of noncovalent hydrogen bonds, the nucleotide alphabet of one-half of the DNA helix determined the alphabet of the other half. Chemistry and dynamics of hydrogen bonding is pivotal in understanding the fundamentals of molecular testing methods, as many procedures are based on the processes of DNA strands’ separation (denaturation) and annealing (renaturation). These processes occur at different temperatures, depending on the total number of hydrogen bonds in

2682_Ch04_077-100 22/05/12 11:40 AM Page 80

80

PART I

Fundamental Concepts

the molecule, which determines the DNA melting point (Tm). The value of Tm is necessary in calculations used to choose temperatures for polymerase chain reaction or other hybridization-based assays.7 DNA melting point has nothing to do with the conversion of solid state into liquid, as the term could imply. Rather, it is the temperature at which half of all hydrogen bonds in the molecule are broken, while the other half are still intact. In other words, the Tm determines how much energy is needed to keep the strands of the helix apart. Temperatures above the Tm promote the separation of the strands, while temperatures below Tm keep the strands together. The Watson-Crick model and the chemistry of hydrogen bonding reveal how DNA could replicate. During replication, the hydrogen bonds break, the strands separate, and each one functions as a template for the synthesis of another complementary half molecule. In this enzymatic process, two identical DNA molecules are generated, each containing the original strand and a new complementary strand. Because each daughter double helix contains an “old” strand and a newly synthesized strand, this model of replication is called semiconservative. The mechanism of DNA replication was studied using cellular components to reconstruct, in vitro, the biochemical reactions that occur within the cell. In this way, the whole process was dissected so that molecular testing procedures could be developed that mimicked the natural process that occurred in vivo. In eukaryotes, DNA polymerase III is able to form a new strand using deoxyribonucleoside triphosphates (dNTPs) as substrates, doublestranded DNA as template, and magnesium as an enzyme cofactor. This enzyme can add nucleotides onto the hydroxyl group (OH) at the 3’ end of an existing nucleic acid fragment. Both strands are synthesized at the same time8 (see Fig. 2–12). The examples of techniques mimicking DNA replication are DNA sequencing and polymerase chain reaction (PCR), described later in this chapter.

Expression of Genetic Information Genes act by determining the sequence of amino acids and therefore the structure of proteins. Knowledge of DNA structure revealed that the genetic information must be specified by the order of the four nitrogen-containing bases (A, C, G, and T). Proteins are polymers of 20 different amino acids, the sequence of which determines their structure and function. But how could the sequence of nucleotides determine the sequence of amino acids? The discovery of the molecular basis of sickle cell anemia provided the first experimental evidence that the nucleotide sequence of a DNA molecule indeed determined the amino acid sequence of a protein. Sickle cell anemia is a genetic disease inherited according to an autosomal-recessive pattern. Patients with this disease have two copies of the mutated beta globin chain gene located on chromosome 11. Individuals with only one mutated copy of the gene show mild or no clinical manifestation and are called carriers. In 1949, Linus Pauling and Vernon Ingram showed that the hemoglobin

of individuals with and without sickle cell anemia had different mobility in an electric field (electrophoretic mobility).9 This indicated that hemoglobin from the patients had a different electric charge; therefore, amino acid composition was different from normal hemoglobin. Carriers of the disease had both types of hemoglobin. In 1957, Ingram identified that substituting valine for glutamic acid in the sixth amino acid position from the NH2 end of the β-globin chain was the cause of the defective hemoglobin.10 Thus, a direct link was established between a gene mutation and the structure of a protein. Concurrent research showed that proteins were synthesized in the cytoplasm in eukaryotic cells. These studies established that the microsomal fraction, which we now call ribosomes, was the major cellular component required for protein synthesis.11 Because DNA was in the nucleus, separated from the cytoplasm by the nuclear membrane, an intermediary molecule had to be responsible for conveying the genetic information from the nucleus to the cytoplasm. Ribonucleic acid (RNA) was a good candidate for this role. Its structure suggested that RNA could be produced based on a DNA template, and RNA was located mainly in the cytoplasm where protein synthesis occurred. Experimental evidence supporting the role of RNA as the intermediary molecule came from the studies on bacterial viruses (bacteriophages). When bacteriophage T4 infects E. coli, the synthesis of bacterial RNA stops, and the only new RNA synthesized is transcribed from T4 DNA. Using radioactive labeling, Sidney Brenner, François Jacob, and Matthew Meselson showed that the newly synthesized T4 RNA associated with bacterial ribosomes, unlike ribosomal RNA.12 These RNA molecules, which served as templates for protein synthesis, were given the name messenger RNAs (mRNAs). But how could nucleotides direct the incorporation of an amino acid into a protein? The experimental answer to this question came again from studying cell-free extracts. In these experiments, a third type of RNA molecule, which we now call transfer RNA (tRNA), was isolated. These were short molecules, 70 to 80 nucleotides long, and some displayed the remarkable characteristic of having amino acids covalently attached to their 3’ end. The enzymes responsible for attaching a specific amino acid to a specific tRNA were also isolated from cell-free extracts and were given the name aminoacyl tRNA synthetases. Sequencing of several tRNAs showed that they all had a common three-dimensional structure, but a unique three-nucleotide-long sequence was always present in a loop region. This sequence, which we now call anticodon, provided the specificity for each tRNA, carrying its specific amino acid, to align with the corresponding codon (triplet) in the mRNA.8 (Refer to Chapter 2 and Figs. 2–15 through 2–18 for more information on the process of translation.) The next question was which triplet of nucleotides of the mRNA corresponded to which amino acid; in other words, it was time to decipher the genetic code. By 1966, Marshall Nirenberg and Har Gobind Khorana had cracked the code. Nirenberg used cell-free extracts containing ribosomes,

2682_Ch04_077-100 22/05/12 11:40 AM Page 81

Chapter 4 Concepts in Molecular Biology

amino acids, tRNAs, and aminoacyl tRNA synthetases, and added synthetic mRNA polymer containing only uracil (-UUUUUU-). He was able to produce in vitro a polymer peptide containing only the amino acid phenylalanine. In this way, he showed that UUU was the codon for phenylalanine.13 During the next few years, all possible mRNA combinations were tried. The 61 different triplets were assigned to their corresponding amino acids, and 3 triplets were found to code for a stop signal (refer to Fig. 2–11). The genetic code is called degenerate because one amino acid may be encoded by more than one nucleotide triplet. This serves as a mechanism that protects the code from devastating effects of mutations occurring in the third or second base of the triplet. In most cases, the mutation results in amino acid change only when it affects the first base of the triplet.

The Central Dogma of Molecular Biology, Expanded Deciphering the genetic code confirmed the central dogma of molecular biology. The genetic material is DNA. DNA is self-replicating and is transcribed into mRNA, which in turn serves as a template for the synthesis of proteins. Although the central dogma remains true, the knowledge acquired in the following years has refined and enlarged it, a process that continues now and into the future. A different method of information flow in biological systems was discovered. A particular group of animal RNA viruses called tumor viruses can cause cancer in infected animals. In the early 1960s, Howard Temin discovered that replication of these viruses required DNA synthesis in the host cells. He formulated the hypothesis that RNA tumor viruses, subsequently called retroviruses, replicated via the synthesis of a DNA intermediate or provirus. In 1970, Temin and David Baltimore showed independently that these viruses contain an enzyme that catalyzes the synthesis of DNA using RNA as a template.14,15 The presence of viral DNA in replicating host cells was also demonstrated. The synthesis of DNA from RNA, now called reverse transcription, was thus definitely established as a mode of biological information transfer. In vitro reverse Figure 4–3. In eukaryotes, the coding sequences (exons) are interrupted by noncoding sequences (introns). Newly transcribed RNA (pre-mRNA) is considered heterogenous RNA (hnRNA) and loses the introns in the process of splicing. The mature mRNA is modified by polyadenylation of the 3’ end and addition of 7-methylguanine “cap” at the 5’ end, and it contains only the exons. In vitro reverse transcription procedures will result in cDNA that corresponds only to sequences originally present within exons. Hence, cDNA is a shorter representation of the gene. (Modified from Buckingham, L, and Flaws, ML: Molecular Diagnostics. Fundamentals, Methods and Clinical Applications. F.A. Davis Company, Philadelphia, PA, 2007.)

81

transcription is an important tool in molecular biology techniques. Natural or recombinant enzymes with reverse transcriptase activity can be used to generate DNA copies of any RNA molecule. Using reverse transcriptase mRNAs can be transcribed to its complementary DNA (cDNA) and studied by recombinant DNA techniques. For example, infectious disease screening assays designed to detect HIV in donors’ blood and other specimens start with the process of reverse transcription, because HIV viruses are retroviruses and their genetic material consists of RNA. (Refer to Chapter 18, “Transfusion-Transmitted Diseases.”) The cDNA synthesized during reverse transcription is subsequently amplified in polymerase chain reaction, which allows for creation of enough copies of genetic material to analyze (refer to “Reverse Transcriptase PCR” section in this chapter). Scientists have added further disclaimers to the central dogma: • Genes are not “fixed.” Some of them do not have a designated chromosomal locus and function as transposable genetic elements in the eukaryotic genome. Another mechanism of physical rearrangement is in vivo DNA recombination. The examples are the immunoglobulin chain and T-cell receptor (TCR) gene rearrangements. • DNA sequences and protein amino acid sequences do not exactly correspond to one another. In many organisms, including humans, coding sequences (exons) are interrupted by noncoding sequences (introns) that are excised from the immature RNA shortly after transcription. This introduces the possibility of alternative splicing to create different proteins from the same gene. Also, different reading frames can generate different mRNAs and therefore different proteins. Viruses frequently use this last mechanism. In vitro reverse transcription procedures will result in cDNA that corresponds only to sequences originally present within exons. Hence, cDNA derived from very long genes is a much shorter representation of the gene (Fig. 4–3). Scientists have discovered further roles for RNA. Some RNA molecules display catalytic activity; by RNA interference, small RNA molecules help to regulate gene expression.16

Promoter

Exon 1

Intron 1

Exon 2

Intron 2

Exon 3

5′ 3′ DNA

3′ 5′

Transcription Pre-mRNA

5′

3′ Processing

mRNA

7 Me G 5′

cDNA

AAAAA 3′ Reverse transcription

2682_Ch04_077-100 22/05/12 11:40 AM Page 82

82

PART I

Fundamental Concepts

Recombinant DNA The classic experiments in molecular biology, which we have described, used simple and rapidly replicating organisms (bacteria and viruses) as study models. However, the genomes of eukaryotes are much more complicated, and scientists had to explore new ways to isolate and study individual genes of these organisms. The big breakthrough came with the development of recombinant DNA technology. A fragment of DNA from

one organism can be cut and pasted into a carrier DNA molecule or vector (e.g., a plasmid or bacteriophage). The new DNA molecule, which is a “recombinant” of the original DNA with the vector DNA, can be introduced using various techniques into another, usually simpler, host organism. Because the genetic code is almost universal, the host organism treats the gene as its own and replicates this “transgene” along with its own DNA. This technique is called molecular cloning. The ABO gene was cloned by Yamamoto’s group in 199017 (Table 4–1).

Table 4–1 Major Events Leading to Establishment of Molecular Immunohematology YEAR

MAJOR EVENT

1924

Bernstein, applying the Hardy-Weinberg principle, proposes that the ABO antigens are coded by one gene.

1944

Avery, MacLeod, and McCarty prove DNA as the carrier of inheritance (following Griffith’s transformation in 1928).

1953

Watson and Crick decipher DNA structure based on Chargaff’s rules (A + G = T + C and T = A and C = G) and x-ray studies by R. Franklin (Nobel ‘62 with Wilkins).

1970

Smith and Wilcox isolate the first restriction enzyme from H. influenzae (RFLP method developed in 1978). Temin and Baltimore discover enzyme reverse transcriptase.

1975

Maxam and Gilbert invent the first DNA sequencing method. Sanger improves it in 1977.

1977–78

First demonstration of a molecular basis for blood group polymorphisms: two aa differences in glycophorin A identified as the basis for M and N blood groups (several researchers).

1981

First demonstration of a molecular basis for rare blood group polymorphisms: basis for Mg and Mc rare blood group variants identified (H. Furthmayr and O. O. Blumenfeld groups).

1986

Kary Mullis publishes polymerase chain reaction (PCR) to amplify DNA fragments using thermostable Taq enzyme.

1986

Glycophorin A and glycophorin C are cloned.

1987

CD55 (DAF) responsible for the Cromer system and glycophorin B are cloned.

1990

F. Yamamoto and colleagues clone the ABO gene. R. D. Larsen and colleagues clone the FUT1 gene (H/h system).

1991

RHD and RHAG genes of the Rh system and KEL gene are cloned.

1992

Higuchi and others at Roche Molecular Systems and Chiron demonstrate real-time PCR (simultaneous amplification and detection).

1994

Genes responsible for the Lutheran system, Colton blood group antigens, and Kidd (JK) system are cloned.

1996

S. Iwamoto and colleagues identify promoter mutations as responsible for the Duffy a-b phenotype.

1999

The Blood Group Antigen Gene Mutation Database (BGMUT) is set up by O. Bloomenfeld and S. K. Patnaik. Moved in 2006 to National Center for Biotechnology Information site at www.ncbi.nlm.nih.gov/gv/mhc/xslcgi.cgi?cmd=bgmut/home.

2000

Complete sequence of the human genome is published.

2004

Consortium for Blood Group Antigens established with the purpose to “provide education for laboratories involved in DNA/RNA testing”; initiative by NYBC (M. Reid). First International Workshop of Molecular Blood Group Genotyping (ISBT initiative).

2005

Microarray-based blood group typing is described by multiple researchers (Transfusion, vol. 45).

2006

Ortho sponsors Rh molecular workshop in Heidelberg. FDA workshop Molecular Methods in Immunohematology (Transfusion, July 2007 suppl) www.fda.gov/downloads/ BiologicsBloodVaccines/NewsEvents/WorkshopsMeetingsConferences/TranscriptsMinutes/UCM054428.pdf. AABB Annual Meeting—BioArray Solutions technology

2007

AABB News publishes “The Omics Revolution”

Modified from: dbRBC, Blood Group Antigen Gene Mutation Database. Historical landmarks in the field of study of blood group systems. Available at www.ncbi.nlm.nih.gov/projects/gv/rbc/xslcgi.fcgi?cmd=bgmut/landmarks

2682_Ch04_077-100 22/05/12 11:40 AM Page 83

Chapter 4 Concepts in Molecular Biology

Cloning is the reproduction of daughter cells from one single cell by fission or mitotic division, giving rise to a population of genetically identical clones. Successive divisions of the host cell create a population of clones containing the DNA fragment of interest. The gene or genes of interest can be studied using the techniques available for the host organism. These techniques have allowed detailed molecular studies of the structure and function of eukaryotic genes and genomes.18

The Coding Sequence of a Gene In humans and most other eukaryotes, the coding part of a gene consists of exons, which in the genomic DNA alternate with noncoding introns. Newly transcribed RNA (pre-mRNA) is considered heterogenous RNA (hnRNA) and loses the introns in the process of splicing. The mature mRNA contains only the exons, the coding sequence of nucleotides that directs the process of translation into the amino acid sequence of the corresponding protein.19 Both the genomic DNA and the coding sequence of a gene can be cloned. First, the mRNA is reverse transcribed in vitro to its cDNA, using either synthetic or retroviral enzyme reverse transcriptase. Because eukaryotic mRNAs end with a poly-A tail, a short synthetic oligo-dT nucleotide can be used as a universal primer starting the cDNA synthesis (this process may also be achieved using the random hexamers or sequence-specific primers, depending on the application). The final product is a hybrid double strand of mRNA and cDNA. The mRNA is degraded, and a DNA strand complementary to the cDNA is synthesized using DNA polymerase. The cDNA, which has the information for the coding gene sequence, can be subjected to the same techniques as genomic DNA.18

Tools for DNA Cloning The following sections describe the essential tools for molecular cloning: restriction endonucleases, gel electrophoresis, vectors, and host cells. An example of gene cloning follows. Restriction Endonucleases The first breakthrough in the production of recombinant DNA came with the discovery and isolation of restriction endonucleases. These enzymes cleave DNA at specific sequences and allow scientists to “cut” a DNA fragment in a controlled and predictable fashion and “paste” it into another fragment using other enzymes (ligases). Restriction endonucleases are isolated from bacteria. From the early 1950s, it was observed that certain strains of E. coli were resistant to infection by various bacteriophages. This form of primitive bacterial immunity was called restriction because the host was able to restrict the growth and replication of the virus. The resistant bacteria had enzymes that selectively recognized and destroyed foreign DNA molecules by cutting it into pieces (endonuclease activity). At the same time, these enzymes modified (by methylation) the host’s chromosomal DNA, protecting it from self-destruction.

83

Numerous restriction endonucleases have been isolated from different bacteria. These enzymes have been classified as type I, II, and III according to their mechanism of action. Only the type II enzymes are relevant for our description of molecular cloning. In 1970, Hamilton Smith and Kent Wilcox at Johns Hopkins University isolated the first type II restriction endonuclease. Type II restriction enzymes are extremely useful for the molecular biologist; they cut DNA at a precise position within its recognition sequence and have no modifying activity.20 More than 200 restriction endonucleases, covering more than 100 different recognition sites, are available commercially. The name given to each enzyme reflects its origin. For example, Smith and Wilcox’s endonuclease was called HindII because it was obtained from Haemophilus influenzae strain Rd. The number II indicates that it was the second endonuclease to be identified in these bacteria. Restriction endonucleases usually recognize sequences 4 to 8 nucleotides in length. The recognition sequences are palindromic; that is, they read the same in the 5’ to 3’ direction on both strands of the double helix. Some enzymes cut both strands in the middle of the target sequence, generating blunt ends. Some enzymes cut both strands off the center, generating staggered ends. For example enzyme EcoRI, isolated from E. coli, recognizes this sequence: 5’GAATTC3’ 3’CTTAAG5’ EcoRI cuts after the first G in both strands, generating fragments with the following ends: 5’G AATTC3’ 3’CTTAA G5’ The single-strand-overhanging ends are complementary to any end cut by the same enzyme. These sticky, or cohesive, ends are extremely useful for “cutting and pasting” DNA from different origins, thus creating recombinant DNA. Examples of other restriction endonucleases and corresponding recognition sequences are listed in Table 4–2. Finding out the sequences in a given DNA recognized by these enzymes, and establishing the distance between such sites, is called restriction enzyme mapping. In case of short sequences (about a few thousand bp long), such as in plasmids, which are bacterial extrachromosomal DNA, the mapping is simple because there are only a few sites recognized by each enzyme. However, restriction maps of long eukaryotic genomes are quite complex. Restriction fragment sizes may be altered by changes in or between enzyme recognition sites. The restriction site may disappear upon various mutations, and a new enzyme recognition site may appear. The discovery of these naturally and pathologically occurring changes contributed to the establishment of the restriction fragment length polymorphism (RFLP) method. The analysis of unique RFLP patterns of various loci proved useful in crime-victim identification and in kinship studies. Blood bank applications of this initially laborious method were expanded greatly after the discovery of polymerase

2682_Ch04_077-100 22/05/12 11:40 AM Page 84

84

PART I

Fundamental Concepts

Table 4–2 Examples of Type II Restriction Endonucleases ENZYME

RECOGNITION SEQUENCE

AluI

AG↓CT

AosI

TGC↓GCA

ApyI

CC↓(A,T)GG

AsuI

G↓GNCC

AsuII

TT↓CGAA

AvrII

C↓CTAGG

BalI

TGG↓CCA

BamHI

G↓GATCC

BclI

T↓GATCA

BglII

A↓GATCT

BstEII

G↓GTNACC

BstNI

CC↓(A,T)GG

BstXI

CCANNNNN↓NTGG

ClaI

AT↓CGAT

DdeI

C↓TNAG

EcoRI

G↓AATTC

EcoRII

↓CC(A,T)GG

Fnu4HI

GC↓NGC

FnuDII

CG↓CG

HaeI

(A,T)GG↓CC(T,A)

HaeII

PuGCGC↓Py

HaeIII

GG↓CC

HhaI

GCG↓C

HincII

GTPy↓PuAC

HindII

GTPy↓PuAC

HindIII

A↓AGCTT

HinfI

G↓ANTC

HpaI

GTT↓AAC

HpaII

C↓CGG

MboI

↓GATC

MstI

TGC↓GCA

NotI

GC↓GGCCGC

PstI

CTGCA↓G

RsaI

GT↓AC

SacI

GAGCT↓C

SacII

CCGC↓GG

chain reaction. For example, the PCR-RFLP method was used to discriminate between RHD+ and RHD genotypes, based on the different number of Pst I enzyme restriction sites in the region flanking the RHD gene (so called Rhesus box).21 Gel Electrophoresis The restriction patterns mentioned in the previous section may be examined by gel electrophoresis (Fig. 4–4), another technique fundamental for DNA cloning. It allows not only for visual analysis of DNA fragments’ length, but also for its isolation and purification for further applications.18 The word electrophoresis means “to carry with electricity.” Agarose gel electrophoresis is a simple and rapid method of separating DNA fragments. The DNA sample is introduced into a well in a gel immersed in buffer and is exposed to electric current. The DNA molecules run at different speeds according to their size. After staining with a fluorescent dye, bands of DNA of specific length can be seen under ultraviolet (UV) light and isolated from the gel. In solution, at a neutral pH, DNA is negatively charged because of its phosphate backbone. When placed in an electric field, DNA molecules are attracted toward the positive pole (anode) and repelled from the negative pole (cathode). To make a gel, molten agarose (a seaweed extract) is poured into a mold where a plastic comb is suspended. As it cools, the agarose hardens to form a porous gel slab with preformed wells. The gel has a consistency similar to gelatin and is placed in a tank full of buffer and with electrodes at opposing ends. The samples containing the DNA fragments are pipetted into the wells, after mixing them with a loading solution of high density, such as sucrose or glycerol. The dense solution helps the DNA sink when loaded into the wells and allows for monitoring of the progress of electrophoresis due to presence of bromophenol blue dye (a tracer). When electric current (80 to 120 V) is applied to electrodes on the tank, the DNA fragments migrate toward the anode. The porous gel matrix acts as a sieve through which larger molecules move with more difficulty than smaller ones. The distance run by a DNA fragment is inversely proportional to its molecular weight and therefore to its length or number of nucleotides. DNA bands can be detected in the gel upon staining with a fluorescent dye, such as ethidium bromide (EB) or SYBR Green. The gel may be soaked in a diluted fluorescent dye solution, or, alternatively, the electrophoresis is run with a gel and buffer containing the dye. EB is a planar molecule, which intercalates between the stacked nucleotides of the DNA helix. This feature makes it a mutagenic factor, which calls for cautious handling of gels, equipment exposed to this agent, and waste. SYBR Green dye isn’t mutagenic, and many facilities have adopted this dye in their staining procedures to assure laboratory safety.22 When the gel is exposed to ultraviolet light of 300 nm, the stained DNA fragments are seen as fluorescent orange (EB) or green (SYBR) bands and can be documented by photography. Each band of DNA is formed by millions of DNA molecules of equal length, which is established by comparison with standard bands of size marker reagents. Gel

2682_Ch04_077-100 22/05/12 11:40 AM Page 85

Chapter 4 Concepts in Molecular Biology Cathode (–)

Anode (+)

EB UV

GEL Figure 4–4. Agarose gel electrophoresis. Negatively charged DNA molecules migrate toward the positive pole. The agarose gel acts as a molecular sieve: The shorter the DNA molecule, the longer the distance of migration. DNA bands are detected by exposure to ultraviolet light (UV) after staining with the fluorescent dye ethidium bromide (EB) or SYBR Green.

85

Direction of DNA Migration

DNA Length

electrophoresis, in low melting point agarose, is used in molecular cloning to isolate and purify the vector and insert, which will be used to form a recombinant DNA vector. Vectors A vector is a DNA molecule of known nucleotide sequence that is used to carry a foreign DNA fragment into a host organism. Vectors can be used to produce large quantities of a target DNA fragment. They can also be used to get a foreign gene expressed in a host cell to study the function of the gene or to manufacture large quantities of the encoded protein product.18 Plasmids. Plasmids are the simplest kind of vectors. They are bacterial, circular genetic elements that replicate independently from the chromosome. The plasmid vectors used in molecular cloning are “designer plasmids,” modified to make perfect recombinant DNA carriers. A vast selection of plasmids are commercially available that are useful for different purposes, such as DNA sequencing, protein expression in bacteria, and protein expression in mammalian cells. All plasmids contain an origin of replication. Plasmid vectors can be under “stringent” control of replication, in which case they replicate only once per cell division. By contrast, the “relaxed” plasmids replicate autonomously and can grow as hundreds of copies per cell. Relaxed plasmids are used to amplify large amounts of cloned DNA. Naturally occurring plasmids contribute significantly to bacterial genetic diversity by encoding functions, such as resistance to certain antibiotics, which provides the bacterium with a competitive advantage over antibiotic-sensitive strains. Plasmids used as vectors also contain genes that encode for antibiotic resistance. When bacteria grow in a culture medium with the given antibiotic, only host cells containing the plasmid will survive. Thus, a pure population of bacteria can be obtained. Examples of antibiotics used for bacterial cloning are listed in Box 4–1. Cloning a DNA fragment requires inserting it into the plasmid vector. Plasmids are designed to contain one or more cloning sites, also called polylinkers, which are a series of recognition sequences for different restriction endonucleases. Most commonly, these are recognition sites for enzymes that cut both strands off the center, which generates cohesive

D N A L E N G T H

(“sticky”) ends. Otherwise, the procedure is called “blunt end cloning.” The circular DNA of the plasmid is cut (or linearized) with a chosen restriction enzyme. The DNA fragment to be inserted is cut with the same enzyme. The sticky ends of the linearized plasmid can form hydrogen bonds with the complementary nucleotides in the overhang of the DNA fragment to be inserted (hence called an insert). Both fragments are run in a preparative, low-melting-point agarose gel. The bands corresponding to the expected size of the linearized plasmid and insert are cut out, and the purified DNA fragments are isolated. Both fragments are “pasted” together with DNA ligase, which forms phosphodiester bonds between adjacent nucleotides (Fig. 4–5). Typical plasmid vectors consist of DNA 2 to 4 kb long and can accommodate inserts up to 15 kb long. Several other vectors are available for cloning fragments of DNA of different sizes. Other Vectors. Lambda (␭) vectors contain the part of the bac-

teriophage’s genome necessary for lytic replication in E. coli and one or more restriction endonuclease sites for insertion of the DNA fragment of interest. They can accommodate foreign DNA 5 to 14 kb long. The recombinant DNA is “packaged” into viral particles and used to infect E. coli. Cosmids are vectors that can accept DNA 28 to 45 kb long. They are useful for producing large-insert genomic libraries. Cosmids have a small region of bacteriophage ␭ necessary for packaging viral DNA into ␭ particles. The linear genomic DNA fragment is inserted into the vector and packaged into bacteriophage particles. After infecting the E. coli cells, the

BOX 4–1

Antibiotics Used in Bacterial Cloning • • • • • •

Ampicillin Carbenicillin Chloramphenicol Hydromycin B Kanamycin Tetracycline

2682_Ch04_077-100 22/05/12 11:40 AM Page 86

86

1

PART I

Fundamental Concepts

EcoRI Digestion Target Gene

GAATTC CTTAAG

Circular Plasmid

r

Amp

GAATTC CTTAAG

ATTC ¬GA TAAG T C ¬

i

Or 5'AATT 3'

Insert

3' TTAA5'

5'AATT 3'

Linearized Plasmid

3' TTAA5'

2 Agarose Gel Electrophoresis (–)

t Targe Gene

T AATAA TT

tract, including carbohydrates, amino acids, nucleotide phosphates, salts, and vitamins. To isolate individual colonies, cells are spread on the surface of agar plates containing an antibiotic used as a selectable marker. A suspension of the cells is diluted enough so that each cell will give rise to an individual colony. Plates are incubated at 37°C. After 12 to 24 hours (at the maximum rate, cells divide every 22 minutes), visible colonies of identical daughter cells appear. Individual colonies are picked and further propagated in liquid culture medium with antibiotic. The incubation proceeds with continuous shaking to maintain the cells in suspension and to promote aeration and production of cell mass that may be used for efficient isolation of vector DNA containing the insert.

Host Cells The recombinant DNA molecule, which was produced in vitro, must then be introduced into a living cell to reveal if it is functional. The typical host organisms are various strains of E. coli. As we have previously described using the Griffith’s experiment, the uptake and expression of foreign DNA by a cell is called transformation.2 However, natural transformation that was observed due to DNA uptake by the rough (nonencapsulated) strain of Streptococcus pneumoniae is a rare event. The efficiency of the bacterial transformation can be increased by chemical or electrical (electroporation) methods that modify the cellular membrane.18 The bacteria treated by these methods are called competent. Because E. coli is a normal inhabitant of the human colon, it grows best in vitro at 37°C in a culture medium containing nutrients similar to those available in the human digestive

DNA Cloning: An Example To summarize the process of DNA cloning, we will describe a hypothetical example in which a gene of interest, or target gene, is obtained from genomic DNA for sequencing purposes. In Figure 4–5, the target gene, flanked by two EcoRI restriction sites, is cut from genomic DNA and inserted into a plasmid vector. The plasmid contains an origin of replication (Ori) so it can be copied by the bacteria’s DNA replication machinery. It also contains a gene that provides resistance to the antibiotic ampicillin (Ampr); therefore, the bacteria that have the plasmid will be able to grow in culture medium with the antibiotic, whereas the bacteria that did not get the plasmid will die. In Figure 4–6, competent E. coli are transformed with the plasmid and plated at a very low dilution in a Petri dish in solid LB medium with ampicillin. Only the bacteria containing

A TT ATT AA

Bacterial artificial chromosomes (BACs) are circular DNA molecules that contain a unit of replication, or replicon, capable of carrying fragments as large as a quarter of the E. coli chromosome. BACs can maintain DNA inserts of up to 350 kb. A typical BAC library contains inserts of 120 kb.

Plasmid Isolation Plasmids can be easily separated from the host’s chromosomal DNA because of their small size and circular structure. A rapid method for making a small preparation of purified plasmid from 1 to 5 mL of culture is called miniprep. The overnight culture is centrifuged, and the pellet containing the bacteria is treated with a solution that includes sodium dodecyl sulfate (SDS) and sodium hydroxide. SDS is an ionic detergent that lyses the cell membrane, releasing the cell contents. Sodium hydroxide denatures DNA into single strands. Treating the solution with potassium acetate and acetic acid (“salting out”), causes an insoluble precipitate of detergent, phospholipids, and proteins and neutralizes the sodium hydroxide. At neutral pH, the long strands of chromosomal DNA renature only partially and become trapped in the precipitate. The plasmid DNA renatures completely and remains in solution. After centrifugation, the pellet is discarded. Ethanol or isopropanol is added to the supernatant to precipitate the plasmid DNA out of the solution. After centrifugation, the DNA pellet is washed with 70% ethanol and dissolved in water or buffer. RNase is used to destroy the RNA that co-precipitates with the plasmid. A miniprep provides enough material for some downstream applications such as sequencing or subcloning into a different plasmid vector. However, it can be easily scaled up to a “midiprep” or “maxiprep” when more plasmid DNA is needed.

(+)

Recombinant Plasmid

3 Elution of insert and Linearized Plasmid

Insert

+

O ri

r

p

Am

4 Ligation Linearized Plasmid

Figure 4–5. Gene cloning: part 1. (1) The target DNA and the vector plasmid are digested with EcoRI. (2) The insert and linearized plasmid are submitted to agarose gel electrophoresis. (3) The bands containing the insert and linearized plasmid are cut from the gel and the DNA fragments eluted. (4) Insert and linearized plasmid are ligated together and a recombinant plasmid containing the target gene is obtained.

vector circularizes into a large plasmid containing the DNA fragment of interest.

2682_Ch04_077-100 22/05/12 11:40 AM Page 87

Chapter 4 Concepts in Molecular Biology 1¬¬¬Transform E. coli with recombinant plasmid Bacterial Chromosome

r

p Am

O ri

Recombinant Plasmid

2¬¬¬Plate bacteria on LB agar medium with ampicillin

3¬¬¬Isolate and grow bacterial colony in liquid medium with ampicillin

4¬¬¬Lyse bacteria and isolate recombinant plasmids

Miniprep

Figure 4–6. Gene cloning: part 2. (1) The recombinant plasmid is used to transform competent E. coli. (2) E. coli bacteria are plated onto solid agar medium containing ampicillin. Only bacteria containing the plasmid survive. Isolated colonies, each from a single cell, grow after overnight incubation at 37°C. (3) A colony is picked and cultured overnight in 1 to 5 mL of liquid LB medium containing ampicillin. (4) The recombinant plasmid is isolated from the bacterial culture (“miniprep”).

the plasmid are able to grow and form colonies, which are visible after overnight incubation at 37°C. A colony is isolated and grown in liquid LB medium with ampicillin. The plasmid replicates independently from the bacterial chromosome, and several plasmids are formed inside each bacterium. From this cell suspension, the recombinant plasmid is isolated. The resulting miniprep contains abundant copies of the gene of interest (target gene) that can be used as a template for obtaining the sequence of the target gene. Currently, all genes coding for the 30 recognized human blood group systems have been cloned.23 Recombinant DNA Libraries A way of isolating single genes is the production of recombinant DNA libraries. Instead of trying to fish one gene out of a mass of genomic DNA or cDNA, each gene is physically separated and introduced into a vector. The target gene is selected by screening each of the individual pieces with a specific probe. Recombinant DNA libraries are collections of clones that contain all genomic or mRNA sequences of a particular cell type. Clones containing a specific gene are identified by hybridization with a labeled

87

probe, such as a cDNA or genomic clone or a PCR product (see the “Detection of Nucleic Acids and Proteins” section). As seen in the section on vectors, different vectors are useful for isolating DNA fragments of different sizes. For example, the Human Genome Project used BAC vectors to produce recombinant human genomic libraries. Genomic DNA was isolated from cells and partially digested with restriction enzymes, obtaining large fragments of around 100 to 200 kb. Inserts of these cloned BACs were subcloned as smaller fragments into phage or plasmid vectors, which were used for sequencing.24 Complementary DNA libraries can be used to determine gene-coding sequences from which the amino acid sequence of the encoded protein can be deduced. Oligonucleotides can be synthesized on the basis of partial amino acid sequence of the protein of interest and used to screen a recombinant cDNA library. The clones that contain the gene encoding the target protein are isolated and sequenced. The complete protein sequence can thus be obtained by translating the mRNA codons into amino acids. This approach was used in 1990 by Fumi-Chiro Yamamoto and his colleagues to isolate the gene that codes for the group A transferase.17 Another approach for isolating a gene on the basis of the protein that it encodes is using antibodies specific against the target protein to screen expression libraries. In this case, the cDNA library is generated in an expression vector that drives protein synthesis in E. coli.

Expression of Cloned Genes: Recombinant Proteins in Clinical Use The cost and effort necessary to isolate proteins with therapeutic functions from their original source make their use impractical. Also, the risk of viral contamination is a fundamental consideration in any therapeutic product that is purified from mammalian cells, in particular from human tissues. For these reasons, the use of engineered in vitro, recombinant proteins is a major improvement in the treatment of several diseases. Large amounts of recombinant proteins can be obtained for biochemical studies or for therapeutic use by molecular cloning of genes that code for them. The cloned gene is inserted into an expression vector, usually a plasmid, which directs the production of large amounts of the protein in either bacteria or eukaryotic cells. A great variety of expression vectors are available for recombinant protein expression in E. coli, yeast, insect cells, and mammalian cells. The list of recombinant proteins used as therapeutic agents increases constantly. Interferon-α used to treat hairy cell leukemia and hepatitis C and B, recombinant hepatitis B vaccine, recombinant antihemophiliac factor, and recombinant coagulation factor IX are some examples of recombinant proteins useful for transfusion medicine. Granulocyte colony-stimulating factor (GCSF) is used to increase the production of hematopoietic stem cells (HSC) for HSC transplantation (HSCT). Epoetin alfa is used to treat anemia caused by chronic renal failure (Box 4–2).

2682_Ch04_077-100 22/05/12 11:40 AM Page 88

88

PART I

Fundamental Concepts

The Polymerase Chain Reaction

BOX 4–2

Recombinant Proteins Used in Transfusion Medicine • • • • • • • • •

Factor VIII Factor IX Factor VII Factor XIII Thrombopoietin G-CSF GM-CSF Epoetin α Interferon-α

G-CSF = granulocyte colony stimulating factor; GM-CSF = granulocyte macrophage colony stimulating factor

Gene Therapy Gene therapy is the introduction of new genetic material into the cells of an organism for therapeutic purposes. In the United States, only somatic gene therapy is allowed in humans—that is, the treated cells are somatic and not germline cells. The obvious clinical use of gene therapy is the treatment of inherited diseases. In the first clinical trial of that kind, the gene coding for adenosine deaminase was introduced into lymphocytes of children suffering from severe combined immunodeficiency disease.25 However, several current clinical trials are focused on oncology. These treatments seek to enhance the host antitumor responses by overexpression of cytokines or by genetic alteration of the tumor cell. One approach is the use of viral vectors, such as retroviruses, adenoviruses, herpesviruses, and lentiviruses. Most human clinical trials to date have used retroviral vectors. However, the use of these vectors carries serious potential risks that must be weighed against the severity of the underlying illness. The exogenous gene may cause disease if overexpressed or expressed in certain cell types. Contaminants may be introduced during vector manufacture. Also of concern is the potential for recombination of gene therapy vectors with human endogenous sequences. The search for better vectors is under way in animal models and holds promise for a safer and more effective gene therapy.

Sense (plus) strand Template DNA 5′

An alternative to cloning for isolating large amounts of a single DNA fragment or gene is the polymerase chain reaction (PCR), which was developed by Kary Mullis at Cetus Corporation in 1985.26 As opposed to cloning, which is performed in a living cell, PCR is carried out completely in vitro. Provided that some sequence of the DNA molecule is known, PCR can be used to amplify a defined segment of DNA several million times. In PCR, DNA (or cDNA) is replicated in the test tube or on a microtiter-like plate, replacing the steps that normally occur within a cell by adding synthetic or recombinant reagents and by cyclic changes in the reaction temperature. The role of the enzyme primase, which in vivo generates the primers to which DNA polymerase attaches the successive nucleotides, is replaced by synthetic oligonucleotides called forward and reverse primers. These primers are usually 15 to 20 nucleotides long and flank the target region to be amplified. In other words, the primers are designed to anneal to complementary DNA sequences at the 3’ end of each strand of the DNA fragment (Fig. 4–7). The product obtained (the amplicon) will have the sequence of the template bracketed by the primers. The two primers are mixed with a DNA sample containing the target sequence; thermostable DNA polymerase; the four deoxyribonucleoside triphosphates (dNTPs); and magnesium, which acts as enzyme cofactor. Thermus aquaticus, a bacterium that grew in hot springs, was the original source of heat-resistant polymerase, consequently named Taq. Currently, numerous recombinant enzymes are on the market. The thermostability of the enzyme is of utmost importance because the first step of the PCR is heat denaturation. Applying high temperatures breaks the hydrogen bonds between the complementary nucleotides and plays the role of the helicases and gyrases that unwind the DNA so that the DNA polymerase complex can reach the template. At 94°C, the double helix is denatured into single strands. In the second step, annealing of the primers to the target sequences flanking the fragment of interest is achieved by cooling to a temperature of 50° to 60°C, which promotes renaturation (reestablishment of hydrogen bonds). The exact optimum temperature of annealing is determined by the number of G and C residues in the primers: The more GC, the more hydrogen bonds to break and the higher melting

Region under investigation

3′ G A A T CG T CG AGC T GC T AGC T T T G T T CG A G A A A C A A Forward 3′ 5′ Primer Primer Reverse 5′ 3′ A T CG T C C T T AGC AGC T CG A CG A T CG A A A C A AGC T 3′ 5′ Template DNA Antisense (minus) strand PCR

Figure 4–7. The FORWARD primer always anneals to the minus strand (also called antisense strand). It is complementary to the 3’ end of the minus strand (and identical to the 5’ end of the plus strand). The REVERSE primer always hybridizes with the plus strand (also called the sense strand). It is complementary to the 3’ end of the plus strand and is identical to the 5’ end of the minus strand. (Modified from Buckingham, L, and Flaws, ML: Molecular Diagnostics. Fundamentals, Methods and Clinical Applications. F.A. Davis Company. Philadelphia, PA, 2007.)

2682_Ch04_077-100 22/05/12 11:40 AM Page 89

Chapter 4 Concepts in Molecular Biology

during PCR is not indefinite; therefore, the theoretical number of product molecules is not reached. After a certain number of cycles, the accumulation of product reaches a plateau, the level of which depends on the initial number of target sequences, the quantity of reagents, and the efficiency of extension. Aside from cloning, the PCR has numerous applications in immunohematology—for example, various modifications of this method have been used in the detection of infectious agents in donors’ blood.27,28 (Refer to Chapter 18.)

point Tm of the molecule. Typically, the optimum annealing temperature is 5 degrees Celsius below the Tm. The third step, primer extension by DNA polymerase, is done at 72°C. This is the optimal temperature for the polymerase, which incorporates nucleotides to the 3’ OH end of the primers using the target DNA as template. The cycles of DNA synthesis, which consist of denaturation, annealing, and extension, are repeated simply by repeating the cycle of temperatures. The reaction is carried out in a programmable heating and cooling machine called a thermocycler. The instrument contains a heating block built from materials characterized by high thermal conductivity (e.g., silver) that allow for rapid changes of temperatures and shortens time between the steps of each cycle. Figure 4–8 shows a schematic PCR reaction. In each cycle, an original template strand is copied to generate a complementary strand, which begins at the 5’ end of the primer and ends wherever the Taq or other thermostable polymerase ceases to function. After the second cycle, DNA is synthesized, using the newly copied strands as templates. In this case, synthesis stops when it reaches the end of the molecule defined by the primer. By the end of the third cycle, a new blunt-ended double-stranded product is formed, with its 5’ and 3’ ends precisely coinciding with the primers. These blunt-ended fragments accumulate exponentially during subsequent rounds of amplification, while the original DNA that was outside the region flanked by the primers isn’t amplified. Thus, the majority of fragments in the later PCR cycles have both ends defined. A single DNA molecule amplified through 30 cycles of replication would theoretically yield 230 (approximately 1 billion) progeny molecules. In reality, the exponential phase of product accumulation

Figure 4–8. Polymerase chain reaction (PCR). Each cycle of PCR consists of denaturation of the double-stranded DNA by heating at 94°C, annealing of the forward and reverse primers to the template by cooling to 60°C, and extension at 72°C of the growing complementary strand catalyzed by the enzyme Taq polymerase. The target DNA sequence, bracketed by the forward and reverse primers, is indicated by a black box in the template DNA. In the third cycle, bluntended double-stranded products (also indicated by a black box) are formed with its 5’ and 3’ ends coinciding with the primers. These target DNA fragments continue to grow exponentially with each cycle.

89

DNA Sequencing Individual fragments of DNA can be obtained in sufficient amount for determining their nucleotide sequence either by molecular cloning or by PCR. Current methods of DNA sequencing are rapid and efficient. The easiest way of determining an amino acid sequence within a protein is the sequencing of a cloned gene, as the coding sequence of a gene can be unequivocally translated into the amino acid sequence of its encoded protein. Modern sequencing is based on the chain termination method developed in 1977 by Fred Sanger at the Medical Research Council’s Laboratory of Molecular Biology in Cambridge, England.29 Just like the PCR, the Sanger sequencing method is a controlled in vitro process mimicking DNA synthesis. When a short synthetic primer (complementary to the beginning of the fragment to be sequenced) is hybridized to a single-stranded template in the presence of the four dNTPs, DNA polymerase can synthesize a new strand of DNA complementary to the template. The addition of an incoming nucleotide occurs via the 3’ hydroxyl group in the deoxyribose

DNA Template¬¬¬¬¬¬¬¬¬+¬¬¬¬¬¬¬¬Forward Primer¬¬¬¬¬¬+¬¬¬¬¬¬Reverse Primer¬¬¬¬¬+¬¬¬¬¬Taq¬¬¬+¬¬¬dNTP's 5’

3’ 5’

3’

5’

3’

5’

3’

1st CYCLE 94°C

TARGET DNA

Denature

5’

3’

3’

5’

60°C

3rd CYCLE 5’ 5’ 3’

Anneal

5’

3’ 5’

3’

3’

5’

3’

3’

5’

3’

5’

5’ 3’ 5’

5’

5’

3’

3’

3’

3’ 5’

2nd CYCLE 72°C

5’

Extend

3’

3’ 5’ 5’

3’

3’

3’

5’

5’

5’ 5’

3’ 5’

3’

3’

5’

3’ 3’

5’

5’ 3’

3

5’

3’

3’

5’ 3’

5’

5’

3’ 5’

3’ 5’

3’ 5’

3’

5’ 3’ 5’

2682_Ch04_077-100 22/05/12 11:40 AM Page 90

90

PART I

Fundamental Concepts

necessary to form the phosphodiester linkage. The principle of Sanger method is based on including small amounts of modified dNTPs that are lacking that hydroxyl group into the reaction mix. These modified dNTPs are 2’, 3’-dideoxyribonucleoside triphosphates. They are designated by a double d (ddNTPs). Upon incorporation into the newly synthesized DNA, they cause an immediate chain termination (hence the name of the method), as no new phosphodiester linkage with the following nucleotide is possible. Originally, Sanger sequencing required using radioisotopes and laborious casting of polyacrylamide electrophoretic gels in which the DNA fragments were separated by size in denaturing conditions created by the presence of urea. Currently, most laboratories are using the automated fluorescent cycle sequencing method (Fig. 4–9). The reaction,

Template 5' ACTGCGGCTACGCCCGTATGCG 3' 3' TGACGCCGATGCGGGCATACGC 5'

Taq Polymerase dNTP's Primer (5' ACTGCGG 3') ddTTP

+

O

94 C Denature

ddATP d dCTP

5' ACTGCGGCTACGCCCGTATGCG 3' 3' TGACGCCGATGCGGGCATACGC 5'

ddGTP

65OC Anneal and Extend 5' ACTGCGG 3' 3' TGACGCCGATGCGGGCATACGC 5' 5' ACTGCGG 5' 5' 5' 5' 5' 5' 5' 5' 5' 5' 5' 5' 5' 5'

Detection of Nucleic Acids and Proteins

3' 3'

The concepts of molecular cloning, creating expression DNA libraries and gene therapy, are fundamental in contemporary molecular research and development setting. Yet cloning may seem esoteric to a clinical laboratorian, presented with the task of identifying a specific mutation or confirming the presence of a pathogen. In the following paragraphs, some classical and newer methods for detecting specific nucleic acids and proteins will be described.

3' 3' 3' 3' 3' 3' 3' 3' 3' 3'

Nucleic Acid Hybridization

3' 3' 3' 25 Cycles

C

T

A

which is carried out in a thermocycler, contains a DNA template, a primer, DNA polymerase, the four dNTPs, and four ddNTPs, each labeled with a different fluorescent dye. The reaction is heated to 94°C, which causes DNA denaturation to a single strand, followed by cooling to 65°C to allow annealing of the primer and its extension by enzymatic addition of nucleotides. Several cycles are repeated. Working from the primer, the polymerase adds dNTPs or ddNTPs that are complementary to the DNA template. The ratio of dNTPs to ddNTPs is adjusted so that a ddNTP is incorporated into the elongating DNA chain, approximately once in every 100 nucleotides. Each time a ddNTP is incorporated, synthesis stops and a DNA fragment of a discrete size, labeled fluorescently according to its last nucleotide, is produced. At the end of 20 to 30 cycles of the reaction, millions of copies of the template DNA sequence are terminated at each nucleotide so a mixture of fragments is obtained, each longer by one nucleotide than the previous one. These fragments are separated by size by capillary gel electrophoresis. The fluorescent labels are detected as the terminated fragments pass a laser aimed at the capillary. When the fluorescent terminators are struck by the laser beam, each emits a colored light of a characteristic wavelength, which is collected by the detector and interpreted by the computer software as A (green), T (red), C (blue), or G (yellow). The final output is an electropherogram showing colored peaks corresponding to each nucleotide position.

C

G

C

C

C

G

T

A

T

G

C

G

Figure 4–9. DNA sequencing: automated fluorescent cycle method. The doublestranded DNA template is denatured by heating at 94°C. Cooling to 65°C allows the annealing of the oligonucleotide primer. In the presence of the four dNTPs and the four fluorescently labeled ddNTPs, Taq polymerase incorporates nucleotides into the growing chain, following the template sequence in a 5’ to 3’ direction. Once in approximately 100 nucleotides, a ddNTP will be incorporated and synthesis will stop. A fragment of DNA is generated that contains a fluorescent tag in its last nucleotide. After capillary gel electrophoresis, the fluorescent labels are detected as the terminated fragments pass a laser aimed at the capillary. The final output is an electropherogram showing colored peaks corresponding to each nucleotide position.

Base pairing between complementary strands of DNA or RNA allows the specific detection of nucleic acid sequences. Double-stranded nucleic acids denature at high temperature (90° to 100°C) and renature when cooled to form doublestranded molecules as dictated by complementary base pairing. This process of renaturation is called nucleic acid hybridization. Nucleic acid hybrids can be formed between two strands of DNA, two strands of RNA, or one strand of RNA and one of DNA. DNA or RNA sequences complementary to any purified DNA fragment can be detected by nucleic acid hybridization. The DNA fragment—for example, a cloned gene or a PCR product—is labeled using radioactive, fluorescent, or chemiluminescent tags. The labeled DNA is used as a probe for hybridization with any DNA or RNA complementary sequence. The resulting hybrid double strand will be labeled and can easily be detected by autoradiography or digital imaging.

2682_Ch04_077-100 22/05/12 11:40 AM Page 91

Chapter 4 Concepts in Molecular Biology

Southern Blotting In this technique developed by E. M. Southern, the DNA analyzed is digested with one or more restriction endonucleases, and the fragments are separated by agarose gel electrophoresis.30 Due to an enormous number of some restriction enzyme recognition sites in genomic DNA, there may be hundreds of various-length fragments running on the gel within a short distance from one another, which upon staining is visible as a “smear” rather than well-distinguished bands. To capture only the fragments of interest, the gel is placed over a nitrocellulose or nylon membrane and overlaid with transfer buffer. The DNA fragments are transferred or “blotted,” when vacuum is applied by the flow of a transfer buffer. The membranebound fragments have the same relative positions as the fragments separated by size on the gel. The filter is then incubated with a labeled probe under very specific temperature conditions. Upon hybridization, the fragments containing the sequence of interest are detected as labeled bands. The classical, laborious, and time-consuming Southern blotting is being replaced by PCR-based detection methods (Fig. 4–10). Northern Blotting This technique is a variation of Southern blotting and is used to detect RNA instead of DNA. Total cellular RNAs are extracted and fractioned by size through gel electrophoresis in the presence of substances, preventing RNA degradation by the ubiquitous RNases. The RNAs are then blotted onto a filter and detected by hybridization with a labeled probe. This technique is used for studying gene expression and is being replaced by quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR).

Figure 4–10. Southern blotting. (1) The DNA restriction digest is submitted to agarose gel electrophoresis. (2) The DNA fragments are transferred from the gel to a filter membrane by flow of buffer with negative pressure under vacuum. (3) The filter is hybridized with a labeled probe, and the labeled DNA bands are detected by digital imaging.

91

DNA Microarrays DNA microarrays, also called gene chips, allow tens of thousands of genes to be analyzed simultaneously.31 A gene chip consists of a glass slide or a membrane filter onto which oligonucleotides or fragments of cDNA, which serve as multiple probes, are printed by a robot in small spots at high density. Because a chip can have more than 10,000 unique DNA sequences, scientists can produce DNA microarrays containing sequences representing all the genes in a cellular genome. A common application of this technique is the study of differential gene expression; for example, the comparison of the genes expressed by a normal cell as opposed to those of a tumor cell. Messenger RNA is extracted from both types of cells, and cDNA is obtained via reverse transcription. The two sets of cDNAs are labeled with different fluorescent dyes (typically red and green), and a mixture of the cDNAs is hybridized to the gene chip that contains many of the probes that represent genes already known in the human genome. The array is analyzed using a laser scanner. The ratio of red to green fluorescence at each specific spot on the array indicates the relative extent of transcription of the given gene in the tumor cells compared with the normal cells. Another application of microarrays, especially desirable in contemporary immunohematology, is the analysis of the genome content rather than its expression. This represents a sophisticated form of genotyping (a process during which polymorphisms within multiple genes may be identified simultaneously). In 2007, a prototype BLOOD-1 Illumina BeadChip microarray-based system was developed in the United States and was used to screen for 18 single nucleotide polymorphisms (SNPs) within genes coding for RBC antigens in the Duffy, Colton, Lewis, Diego, and other blood groups.32

1 Agarose gel electrophoresis Gel Cathode (–)

2 Blotting with transfer buffer

Filter Sealing Mask Sealing Frame Porous Support Vacuum

Gel

3 Hybridization with probe and detection

Anode (+)

Filter

2682_Ch04_077-100 22/05/12 11:40 AM Page 92

92

PART I

Fundamental Concepts

GenomeLab SNPStream by Beckman Coulter is another example of microarray technology that was customized for RBC antigen typing at the Genome Quebec Innovation Center, Canada.33 Fluorescent In Situ Hybridization In this technique, scientists use fluorescent probes to detect homologous DNA or RNA sequences in chromosomes or intact cells. In this case, the hybridization of the probe to specific cells or subcellular structures is determined by direct microscopic examination. In 1995, this method was used to localize the ABO gene to chromosome 9.34

PCR-Based and Other Amplification Techniques Amplification of DNA by PCR allows the detection of even single copies of DNA molecules. By contrast, Southern blotting has a detection limit of around 100,000 copies. The specificity of the PCR amplification depends on the primers that hybridize to complementary sequences of the template molecule spanning the target DNA fragment. With carefully chosen primers, PCR can be used to selectively amplify DNA molecules from complex mixtures, such as genomic DNA from cell extracts. Real-Time PCR In real-time PCR, conducted in a special type of thermocycler (LightCycler), the product formed during each cycle of amplification is detected by fluorescence at the same time that it is produced. In addition to primers, the real-time reaction mixture contains DNA probes that are complementary to the region between the primers (called TaqMan or molecular beacons or FRET probes), labeled with fluorophores that emit fluorescent light when binding to the newly synthesized amplicon. If the assay is used to detect polymorphism, a post-PCR monitoring of amplicon/probe separation upon slow increase of temperature is performed. This process is called melting curve analysis and allows for determination of homo- or heterozygosity. A classical example of melting curve analysis is the detection of factor V Leiden mutation in patients with this inherited coagulopathy.35 Real-time PCR allows the quantification of specific mRNAs in complex mixtures and is extremely useful in the study of gene expression when combined with reverse transcription. Reverse Transcriptase PCR Single copies of RNA can be detected by adding a step of cDNA synthesis by reverse transcription (RT), prior to the PCR amplification (RT-PCR). By RT-PCR, cDNA molecules can be specifically amplified from total RNA obtained from cell extracts, tissue sections, or plasma. The high sensitivity of PCR-based DNA and RNA detection techniques makes them valuable for early detection of transfusion-transmitted viruses, such as HIV and hepatitis B and C. The first RT-PCR assays developed by National Genetics Institute (UltraQual HIV-1) and by Roche (COBAS AmpliScreen HIV-1) were designed to detect these pathogens in donors’ blood and were approved by the FDA in 2001 and 2003.28,36 Real-time RT-PCR is employed in the multiplex assay for

concurrent detection of HIV, HCV, and HBV (Roche Cobas TaqScreen MPX).37 Transcription Mediated Amplification Other FDA approved tests for HIV, HCV, HBV, and West Nile virus in donors’ blood are performed by means of another method developed by Gen-Probe: transcription mediated amplification (TMA). The starting material in this assay is RNA. The RNA serves as a template for a reverse transcriptase to synthesize a complementary DNA, which is bound to the RNA by hydrogen bonds to form a RNA/DNA hybrid. The DNA is never amplified in the assay. After enzymatic removal of the RNA from the hybrid, the DNA is transcribed to hundreds of RNA molecules. These multiple RNA molecules go through another reverse transcription process to produce more RNA/DNA hybrids, and the whole process is repeated many times. The detection of the pathogen (if its RNA is present in the sample) occurs via hybridization protection assay (HPA) technology. In this technology, ssDNA probes labeled with chemiluminescent molecules are added to form hybrids with the amplified RNA molecules produced during TMA. Light is emitted upon hybridization of the probes to the RNA and captured by a luminometer. Nucleic acid testing (NAT) is rapidly becoming a standard method in blood banking. It allows the detection of pathogens before the appearance of a testable immune response, such as screening of antibodies. Narrowing the preseroconversion window (during which donors can be infected but do not yet test positive by serologic methods) helps to enhance the safety of blood products.38,39 Since NAT implementation, the average seroconversion window for HIV has been shortened to 11 days (as compared to 22 days when using serologic testing and 16 days when performing the standard confirmatory p24 antigen testing). The average seroconversion window for HCV has been shortened to 10 days (as compared to the original 82 days when serologic testing is used). Consequently, the residual risk of HIV transmission decreased from 9.7 to 1.2 incidents per million donations, and the residual risk of HCV transmission decreased from 2 to 1 incident per million donations. A significant progress in testing for the transfusion-transmitted pathogens in donor units was the ability of the NAT assays to detect these pathogens concurrently. In 2008, the GenProbe assay, initially approved for detection of HIV-1 and HCV only, was also approved for the detection of HBV.36

Antibodies as Probes for Proteins Gene expression at the protein level can be studied by using labeled antibodies as probes. In particular, monoclonal antibodies are widely used in the technique called immunoblotting.40 This technique is also known as Western blotting by analogy to Southern and Northern blotting. Proteins in cell extracts are separated by polyacrylamide gel electrophoresis in the presence of the ionic detergent SDS. In SDS-PAGE electrophoresis, each protein binds many detergent molecules, which causes its denaturation and provides a negative charge. Proteins will migrate to the anode; the rate of migration depends on their

2682_Ch04_077-100 22/05/12 11:40 AM Page 93

Chapter 4 Concepts in Molecular Biology

size. The proteins are then transferred from the gel onto a filter membrane. The protein/antigen of interest is detected by incubation of the membrane with a specific labeled antibody. An example of Western blot is the HIV p24 confirmatory testing.

93

DRw52 LRS PROBE

Techniques for Studying Gene Polymorphism By recombinant DNA techniques, experimental analysis proceeds either from DNA into protein or from protein into DNA. An important consequence for transfusion medicine has been the introduction of techniques for typing molecular polymorphism, not only at the protein level but also at the genetic level. These techniques are usually grouped under the name of DNA typing.

Restriction Fragment Length Polymorphism Restriction Fragment Length Polymorphism (RFLP) can be used to detect the glycosyl transferase gene in a person who is type AO or BO. The nucleotide deletion of the O allele results in the loss of a BstEII site (GGTGACC) and creation of a new KpnI site (GGTACC). RFLP can also be used to determine if an individual carries the mutation for sickle cell anemia. The gene that codes for hemoglobin S (HbS) has one nucleotide difference with the normal β-globin coding allele. The sixth codon of the defective gene is GTG (Val). The sixth codon of the normal gene is GAG (Glu). The restriction site for MstII (CCTGAGG) is lost in the mutated gene (CCTGTGG). RFLP is widely used in HLA typing for transplantation (Fig. 4–11), in paternity testing and in forensic science (refer to Chapter 22, “Relationship Testing”).

PCR and Allele-Specific Probes PCR can be used to amplify polymorphic genes from genomic DNA. The PCR products are blotted on a nylon filter and hybridized with specific probes that allow the distinction of the different known alleles. This method, usually called dot blotting or sequence-specific oligonucleotide probe (SSOP), is commonly used for HLA typing (Fig. 4–12).

Figure 4–12. Sequence-specific oligonucleotide probe (SSOP). Dot-blot of PCR products hybridized to an allelic-specific HLA probe.

A variation of this method is sequence-specific PCR (SSP), in which the alleles are distinguished by PCR amplification with primer pairs specific for one allele or a group of alleles. Genomic DNA is submitted to PCR amplification with a battery of primer pairs. The products of the different PCR reactions are run in an agarose gel and stained with EB or SYBR Green. The presence of fluorescent bands of a defined size in the gel indicates the presence of the allele for which the primer pair is specific (Fig. 4–13).

DNA Sequencing Alleles of polymorphic genes can also be specifically amplified by PCR and sequenced after cloning into plasmid vectors. Alternatively, direct sequencing of PCR products can be done without previous cloning, if the product obtained is pure enough. This procedure is currently used in

DRB1*13

DQB1*03

Figure 4–11. Restriction fragment length polymorphisms (RFLPs). Southern blot analysis of genomic DNA to determine HLA-DR genotype.

DRB1*08

DQB1*04

DRB3*00

Figure 4–13. Sequence-specific PCR (SSP). Genomic DNA was PCR amplified with primer pairs specific for different HLA class II alleles or group of alleles. Note the control band indicating successful PCR. (Courtesy of HLA laboratory, Department of Transfusion Medicine, NIH.)

2682_Ch04_077-100 22/05/12 11:40 AM Page 94

94

PART I

Fundamental Concepts

HLA typing for allogeneic hematopoietic stem cell transplant (HSCT).

DNA Profiling or “Fingerprinting” Minisatellites and microsatellites are regions of DNA interspersed in the human genome formed by variable number of tandem repeats (VNTRs) of short nucleotide sequences. The variability depends on the number of repeat units contained within each “satellite.” Minisatellites or variable tandem repeats are composed of repeated units ranging in size from 9 to 80 bp. Microsatellites or short tandem repeats (STRs) contain repeat units of 2 to 5 nucleotides. The polymorphism of these loci in the human population is so high that there is a very low probability that two individuals will have the same number of repeats. When several loci are analyzed simultaneously, the probability of finding two individuals in the human population with the same polymorphic pattern is extremely low. The independence of inheritance of the different loci tested is ensured by choosing loci on different chromosomes. The pattern of polymorphism (the differences in number of repeats or length) can be determined by RFLP or PCR analysis. In 1997, the Federal Bureau of Investigation recommended a panel of 13 STRs, plus an XY marker, for criminal investigations. With this number of independently inherited polymorphisms, the probability of even the most common combinations is less than 1 in 10 billion. Thus, modern DNA testing can uniquely identify each person, hence the name DNA fingerprinting. DNA profiling is used in forensic applications, paternity testing, and to follow chimerism after HSCT.

Systems Biology The molecular techniques developed in recent years and older techniques, still valuable in the study of nucleic acids and the cellular processes they are involved in, keep improving and expanding. Many are being automated and miniaturized. While it is necessary to have the exact sequence of DNA that is of interest (e.g., if it is associated with an inherited disease), it is equally important to understand how that DNA is expressed inside of a living cell. As technology is developed, it will be interesting to see what new methods become available and occur in common use. Of particular interest to biotechnology is the development of nanotechnology and nanostring technology applications, high throughput DNA systems, and computational bioinformatics in which complex models of expression and regulation (such as proteasomes) are being assembled and analyzed. Some of the most exciting recent advances in molecular biology have been the result of analyzing the complete nucleotide sequence of the human genome. A draft sequence of the human genome was published in 2001 by two independent teams of researchers.24,41 The public effort was led by the International Human Genome Project, which used BAC libraries (briefly described in the “Tools for DNA Cloning” section). The other group, led by Craig Venter of Celera Genomics, used a “shotgun” approach in which small fragments of genomic DNA were cloned and sequenced.

Overlaps between the fragment sequences were used to assemble the whole genome. This draft encompassed about 90% of the euchromatin portion of the human genome. Continuing work by researchers around the world rendered a high-quality human genome sequence in 2003—50 years after the Nature paper in which Watson and Crick described the structure of DNA. This wealth of information, which is constantly updated, can be accessed through the National Center for Biotechnology Information (NCBI) website (www.ncbi.nlm.nih.gov).42 In its first 50 years, molecular biology has been primarily an analytical science, concerned mainly with reducing biological problems to the level of individual genes. This approach has been extraordinarily successful in finding the key genes involved in cellular replication and development and in identifying the genes involved in genetic disorders. The challenge for the next few decades is going to be understanding the synchronized activity of numerous genes during key biological events, such as development and memory, and understanding the multiple genes presumably involved in complex diseases such as cancer and diabetes. Another complication is the fact that several different proteins can be produced from a single gene by alternative RNA splicing and that additional forms are created by post-translational modifications. To solve these complex issues, biologists are turning to more synthetic approaches that allow them to examine the coordinated expression of multiple genes. Experiments performed using DNA and protein chips are starting to show how hundreds or thousands of genes are expressed coordinately in response to different developmental and environmental stimuli. Analysis of these data is one of the applications of bioinformatics, a discipline that uses computer algorithms to manage and analyze large-scale experiments. The functions of genes implicated in a specific pathway can be further explored by reverse genetics. Genes can be “knocked out” or “knocked in” as wild type or mutated into the germline of a mouse or other animal model.43,44 The resulting knockout transgenic animal can be analyzed for metabolic or behavioral changes, which can give clues to the mechanism of function of the gene under study. A novel way of studying specific gene function is RNA interference, by which small synthetic RNA molecules can be used to silence a specific target gene.16 This new biology that is emerging is called systems biology, and it requires integration of knowledge from experiments done in vitro, in vivo, and in silico (in a computer).

Red Cell Genotyping Molecular RBC antigen typing could be of tremendous advantage in situations where serologic testing is impossible or inconclusive. Currently considered as supplemental rather than routine practice, it has the potential to revolutionize the way blood cell inventory may be searched for multiple antigen-negative units. The knowledge of theoretical principles and practical skills to perform red cell genotyping are becoming indispensable in contemporary blood banking.

2682_Ch04_077-100 22/05/12 11:40 AM Page 95

Chapter 4 Concepts in Molecular Biology

Genetic Basis of Blood Groups Early important events in the molecular biology of transfusion medicine includes the cloning and sequencing of the gene that codes for the MN polymorphism, GYPA, in 1986, followed by the ABO gene in 1990 (review Table 4–1). Now the genes for all the blood group systems have been identified and localized in specific chromosomal regions.23 Also known are the alleles that code for the blood group polymorphisms, the structure of the gene products, and in many cases their function. This knowledge has allowed the development of red cell group typing at the DNA level. Molecular genotyping is being increasingly used in clinical blood banking, where it does not replace but complements traditional phenotyping. Molecular biology provides information to help make decisions in transfusion medicine, such as obtaining compatible blood in cases of massive transfusion or transplantation. The field of molecular biology is constantly changing and improving. Methods become more efficient and less expensive. As greater numbers of populations are analyzed, different alleles are discovered and added to databases that are updated frequently. A committee of the International Society of Blood Transfusion (ISBT) is responsible for the nomenclature of red cell surface antigens. A monograph published in 2004 described the ISBT terminology for red cell surface antigens and genes and tabulated a complete classification.45 Since then, two updates have been published.46,47 The full current classification can be found at the ISBT/IBGRL website (http://ibgrl.blood.co.uk/).48 Most of the blood group systems are coded by variants of a single gene. There are four exceptions: Rh; Xg; Chido/Rodgers, which have two genes each; and MNS, which has three. As an example, the Rh system consists of two genes: D and CE. These genes have 97% homology, which can add difficulty in molecular methods for genotyping this system. Table 4–3 enumerates the blood group systems, their genes with the chromosomal location, and the corresponding antigens.

Molecular Basis of Blood Group Polymorphism According to the Blood Group Antigen Gene Mutation Data base (dbRBC) as of July 7, 2010, there were 30 blood group systems, 39 genes, and 1,165 alleles known in the human population. The dbRBC contains a complete collection of genes and alleles and provides comprehensive information on blood groups antigens.49 It is frequently updated and provides DNA sequences and alignments. The systems ABO, P, Lewis, H, I, and MNS comprise antigens that are carbohydrates on glycoproteins or glycolipids. The genes that constitute these systems code for glycosyltransferases that catalyze oligosaccharide chain synthesis. For the rest of the blood group systems, the antigens are direct consequences of amino acid variation in the protein sequence. Most blood group variants are the result of one or more single nucleotide polymorphisms (SNPs) encoding amino acid substitutions in a glycosyltransferase

95

or the extracellular domain of a membrane protein. Other mechanisms of polymorphism generation are gene deletion, single nucleotide deletion, insertion, and intergenic recombination. Clinically significant blood group systems are listed in Table 4–3.

Clinical Applications of Red Cell Genotyping There are several important applications for red cell genotyping in use today.50,51 These methods help to confirm serologic testing. In cases where serology is not possible or not sensitive enough or where discrepancies occur, genotyping provides results that can be used to obtain a blood type on a donor or patient. Applications of genotyping include fetal DNA typing, blood group typing of donors for alloimmunized patients, screening blood donors to locate rare blood group phenotypes, screening blood inventory for antigennegative units, determining the frequency of blood group polymorphisms in a given population, determining zygosity for the fathers of fetuses at risk for hemolytic disease of the fetus and newborn (HDFN), and blood group typing of patients with autoimmune hemolytic anemia and other diseases. Fetal DNA Typing Initially, ABO and Rh typing should be done on a pregnant mother and should include an antibody screening. If the woman is D negative and has a negative antibody screen using IgG AHG techniques, she is a candidate for RhIG. If the antibody screening is positive, then the antibody specificity must be determined. If the father has the corresponding antigen, then his zygosity, either heterozygous or homozygous, should be established. If the father is heterozygous, then the genotype of the fetus can be determined using PCR testing of amniocentesis samples, chorionic villus sampling, or cordocentesis samples. PCR has a very high sensitivity, approaching 100%, and a low false-negative rate, so it is an excellent method. DNA probes are known for most if not all genes playing a role in HDFN. As an alternate approach, the typing for the D antigen at the molecular level can be done on maternal samples as early as the second trimester. Fetal DNA in maternal samples is derived from apoptotic syncytiotrophoblasts; it increases in concentration throughout pregnancy and is cleared soon after delivery. Maternal-only, sample DNA testing will likely become more routine in the near future, as it has many advantages. All DNA-based information allows earlier intervention in cases where HDFN is suspected.52 (Refer to Chapter 19, “Hemolytic Disease of the Fetus and Newborn [HDFN].”) In addition to HDFN, there is risk to the developing fetus in cases of platelet and neutrophil antigen incompatibility, resulting in fetal and neonatal alloimmune thrombocytopenia (FNAIT) and neonatal alloimmune neutropenia (NAN). Genotyping can help resolve these cases and determine if there is an associated risk due to maternal platelet and neutrophil antigens and HLA type.

2682_Ch04_077-100 22/05/12 11:40 AM Page 97

Chapter 4 Concepts in Molecular Biology

Extensive Blood Group Typing of Donors for Alloimmunized Patients Patients with multiple antibodies may require extensive testing to find compatible blood for transfusion. It is now possible to genotype potential donors and the patient to prevent further immunization and to characterize the donor at a more specific level.53 DNA testing can be done in place of extensive family studies to determine the genotype. Sequencing of the entire gene of interest, often required to obtain sufficient information, may be labor-intensive. The amount of work may be lessened if exon sequencing is done first and if RFLPs can be done on certain areas of the gene at the beginning of the study. Focused sequencing with comparisons to antigenic profiles can also be used. Having extensive information on the patients’ and the potential donors’ genotypes allows transfusion to take place in a safer environment. Knowing the antigens that the patient does not have based on genotyping prevents further alloantibodies from being made from the transfusion of blood that is positive for these antigens. Because red cells have lost their nuclei, white cells can be used for genotyping and other normal adult diploid cells. Screening of Blood Donors to Find Rare Blood Group Phenotypes Using DNA-based methods to screen blood donors allows for a high-throughput system screening in comparison with serology-based methods. Blood group antisera often are not readily available for rare blood group phenotypes or are prohibitively expensive to use on a large scale. Genotyping with PCR techniques allows for the probes (or primers) to be synthesized at low cost and used in DNA-based methods, as long as information about the sequence of the gene is known. Different alleles can be tested at the same time in the multiplex PCR assays or on microarrays. Once known, the genotype information can be put into a database and does not require repeated testing, which saves considerable time and money. A rare donor profile can be generated, linking potential donors to potential recipients for better recruitment in cases of emergency. For patients requiring donor units with rare phenotypes, the costs and time involved in genotyping such donor units are acceptable.

97

Determining the Frequency of Blood Group Polymorphisms in a Population Genotyping databases can be used to predict the possibility of finding a specific allele in a given population once a similar population has been analyzed at the genotype level. Because most blood group alleles are the result of a single nucleotide polymorphism, screening of blood samples for allele frequency can be relatively easy and done by simple DNA-based methods. Several different methods employed for this include RFLP and SSP-PCR (single or multiplex), real-time quantitative PCR, sequencing and microarray technology using DNA probes on chips. Blood Group Typing of Patients With Autoimmune Hemolytic Anemia and Other Diseases Patients with autoimmune hemolytic anemia and other conditions such as sickle cell anemia can have trouble obtaining compatible donor units. They are often sensitized to many antigens and have a rapid turnover of red cells, requiring frequent transfusion. Because they can have a complex population of red cells, with autologous cells mixed with transfused cells from more than one donor, genotyping methods are an excellent way to type these donors. A small amount of patient white cells or cheek cells can be used to determine the genotype using standard DNA-based methods, and the subsequent patient phenotype can be determined from the genotype. Although crossmatching may not provide totally compatible results, especially with autoimmune diseases, at least alloantigens can be ruled out when transfusion is required, thereby preventing further alloimmunization in an already-difficult-to-transfuse patient. In addition to saving the time required for repeated adsorptions, elutions, and extensive phenotyping in these patients and in donor units, the information obtained by DNA-based methods is highly accurate and easy to obtain. It is a permanent record of the patient’s genetic profile, and it is necessary information in cases where transplant may be considered. It is also a permanent record of the donor’s profile when performed.

SUMMARY CHART

   

The central dogma of molecular biology: DNA → RNA → protein. Proteins have structural, enzymatic, and gene-regulatory function. Through these mechanisms, the genotype of a cell is translated into its phenotype. DNA is the genetic material. DNA is a double helix, consisting of two antiparallel strands of stacked nucleotides paired through hydrogen bonds. Adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G).

The structure of DNA determines its function. The sequence of nucleotides of one strand determines the sequence of its complementary strand, the basis for the semiconservative way of replication. A gene is transcribed into precursor RNA, and the spliced mRNA is translated into the amino acid sequence of the coded protein. The sequence of mRNA unequivocally determines the sequence of the protein.

Continued

2682_Ch04_077-100 22/05/12 11:40 AM Page 98

98

PART I

Fundamental Concepts

SUMMARY CHART—cont’d

   

  

Recombinant DNA is the DNA of one organism “cut and pasted” into a carrier vector. The foreign gene introduced in a host organism is functional because the genetic code is universal. By DNA cloning, recombinant genes of complex animals, such as humans, are introduced into simple organisms, such as bacteria, and other model organisms, such as mice, allowing structural and functional studies. Restriction endonucleases, bacterial enzymes that recognize and cut specific DNA sequences, are fundamental tools for DNA cloning. Gel electrophoresis separates nucleic acids by size. The most common host cell is the bacterium E. coli. Plasmids, the most commonly used vectors, are independently replicating circular DNA molecules modified to provide the host cell with resistance to antibiotics (selectable marker) and one or more restriction enzyme sites for inserting the recombinant gene. By reverse transcription, mRNA is transcribed into complementary DNA (cDNA). Automated fluorescent DNA sequencing based on the Sanger dideoxy, chain termination method is a standard laboratory procedure. DNA sequencing of a cloned cDNA corresponding to a given gene is the easiest way to determine the amino acid sequence of a protein.

Review Questions 1. The central dogma of molecular biology states that: a. b. c. d.

DNA is the genetic material RNA is the genetic material DNA is translated to mRNA Proteins are transcribed from mRNA

2. Recombinant-DNA technology is possible because: a. b. c. d.

Restriction endonucleases cut RNA Restriction endonucleases cut proteins The genetic code is universal Bacteria are difficult to culture

3. Agarose gel electrophoresis is a technique used for: a. b. c. d.

DNA synthesis RNA synthesis Separation of DNA molecules by size Oligonucleotide synthesis

4. Restriction fragment length polymorphism (RFLP) is

based on the use of the enzymes: a. Reverse transcriptases b. Bacterial endonucleases c. DNA polymerases d. RNA polymerases

    

 

Genomic and cDNA libraries are collections of clones containing the genetic material of a cell. Base pairing between complementary strands of DNA or RNA (hybridization with a labeled probe) is used to detect specific nucleic acid sequences in complex mixtures. Southern blotting, Northern blotting, and dot blotting are hybridization-based techniques for nucleic acid sequence-specific recognition. The polymerase chain reaction (PCR) is an in vitro method for DNA amplification. Molecular polymorphism is studied at the genetic level by DNA typing. Methods for DNA typing relevant for transfusion medicine are restriction fragment length polymorphism, allele-specific oligonucleotide probe hybridization, allele-specific PCR amplification, DNA sequencing, and DNA profiling (DNA fingerprinting). PCR and TMA are used for the early detection of transfusion-transmitted pathogens. Other therapeutic uses of molecular biology are gene therapy and the clinical use of recombinant proteins, such as interferons, coagulation factors, and growth factors. Molecular RBC antigen typing is used to either confirm serologic testing or in cases where serology is not possible or is not sensitive enough or where discrepancies occur.

5. The polymerase chain reaction (PCR): a. b. c. d.

Is carried out in vivo Is used for peptide synthesis Requires RNA polymerase Is used for the amplification of DNA

6. Plasmids are: a. b. c. d.

Vectors used for molecular cloning Antibiotics Enzymes Part of chromosomes

7. Some model organisms: a. b. c. d.

Simplify the study of human disease Are used to produce recombinant proteins Are prokaryotes and some are eukaryotes All of the above

8. DNA sequencing: a. b. c. d.

Is more difficult than peptide sequencing Requires the use of RNA polymerase Can never be automated Is an enzymatic in vitro reaction

2682_Ch04_077-100 22/05/12 11:40 AM Page 99

Chapter 4 Concepts in Molecular Biology

9. RFLP and SSP are techniques used for: a. b. c. d.

Protein isolation RNA isolation DNA typing Protein typing

10. Recombinant DNA techniques: a. b. c. d.

Are not used in a clinical setting Are useful research tools Are not used in blood banking Are useful only for research

11. Transcription mediated amplification: a. b. c. d.

Requires thermostable DNA polymerase Is an isothermal procedure Is an obsolete method currently replaced by SSOP Utilizes probes labeled with fluorescent tags

12. Preseroconversion window: a. Is the time when donors can be infected but do not

yet test positive by serologic methods b. May be narrowed by using molecular methods c. Refers mainly to viral pathogens d. All of the above

13. Red blood cell molecular antigen typing is useful in all

listed situations except: a. In screening RBC inventory for antigen-negative units b. When reagent antibodies are weak or unavailable c. In quantitative gene expression analysis d. When resolving ABO discrepancies

References 1. Crick, F: Central dogma of molecular biology. Nature 227(5258):561–563, 1970. 2. Griffith, F: The significance of pneumococcal types. J Hyg (Lond) 27(2):113–159, 1928. 3. Avery, OT, MacLeod, CM, and McCarty M: Studies on the chemical nature of the substance inducing transformation of pneumococcal types. Induction of transformation by a desoxyribonucleic acid fraction isolated from Pneumococcus type III. J Exp Med 1;79(2):137–158, 1944. 4. Hershey, AD, and Chase, M: Independent functions of viral protein and nucleic acid in growth of bacteriophage. J Gen Physiol 36(1):39–56, 1952. 5. Chargraff, E, Magasanik, B, Visher, E, Green, C, Doniger, R, and Elson, D: Nucleotide composition of pentose nucleic acids from yeast and mammalian tissues. J Biol Chem 186(1):51–67, 1950. 6. Watson, JD, and Crick, FHC: Molecular structure of nucleic acids: A structure for deoxyribose nucleic acid. Nature 171:737–738, 1953. 7. Breslauer, KJ, et al: Predicting DNA duplex stability from the base sequence. Proc Natl Acad Sci USA 83(11):3746–3750, 1986. 8. Lewin, B: Genes VIII. Prentice Hall, New York, 2004, p 392. 9. Pauling, L, Itano, HA, et al: Sickle cell anemia a molecular disease. Science 110(2865):543–548, 1949. 10. Ingram, VM: Gene mutations in human hemoglobin: The chemical difference between normal and sickle cell hemoglobin. Nature 180:326–328, 1957. 11. Keller, EB, Zamecnik, PC, and Loftfield, RB: The role of microsomes in the incorporation of amino acids into proteins. J Histochem Cytochem 2(5):378–386, 1954.

99

12. Brenner, S, Jacob, F, and Meselson, M: An unstable intermediate carrying information from genes to ribosomes for protein synthesis. Nature 190:576–581, 1961. 13. Nirenberg, M, and Leder, P: RNA codewords and protein synthesis. Science 145:1399–1407, 1964. 14. Temin, HM, and Mizutani, S: RNA-dependent DNA polymerase in virions of Rous sarcoma virus. Nature 226:1211–1213, 1970. 15. Baltimore, D: RNA-dependent DNA polymerase in virions of RNA tumour viruses. Nature 226:1209–1211, 1970. 16. Sharp, PA: RNA interference—2001. Genes Dev 15:485–490, 2001. 17. Yamamoto, F, et al: Cloning and characterization of DNA complementary to human Histo-blood group A transferase mRNA. J Biol Chem 265:1146–1151, 1990. 18. Sambrook, J, and Russell, DW: Molecular Cloning: A Laboratory Manual, 3rd ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 2001. 19. Alberts, B, et al: Molecular biology of the cell, 4th ed. Garland Publishing, New York, 2002. 20. Nathans, D, and Smith, HO: Restriction endonucleases in the analysis and restructuring of DNA molecules. Ann Rev Biochem 44:273–293, 1975. 21. Wagner FF, and Flegel, WA: RHD gene deletion occurred in the Rhesus box. Blood 95:3662–3668, 2000. 22. Kirsanov, KI, Lesovaya, EA, Yakubovskaya, MG, and Belitsky, GA: SYBR Gold and SYBR Green II are not mutagenic in the Ames test. Mutat Res 699(1-2):1–4, 2010. 23. Logdberg, L, Reid, M, and Zelinski, T: Human blood group genes 2010: Chromosomal locations and cloning strategies revisited. Transfus Med Rev 25(1):36–46, 2011. 24. International Human Genome Sequencing Consortium: Initial sequencing and analysis of the human genome. Nature 409:860–921, 2001. 25. Gaspar, HB: Bone marrow transplantation and alternatives for adenosine deaminase deficiency. Immunol Allergy Clin North Am 30(2):221–236, 2010. 26. Saiki, RK, Gelfand, DH, Stoffel, S, Scharf R, Higuchi, R, Horn, GT, et al: Primer-directed enzymatic amplification of DNA with a thermostable DNA polymerase. Science 239:487–491, 1988. 27. Busch, MP, and Kleinman, SH: Nucleic acid amplification testing of blood donors for transfusion-transmitted diseases. Report of the Interorganizational Task Force on nucleic acid amplification testing of blood donors. Transfusion 40:143–159, 2000. 28. Kraj, B, and Nadder, T: Blood donor screening process and infectious disease testing using molecular methods. Advance for Medical Laboratory Professionals, 17–20, October 8, 2007. 29. Sanger, F, Nicklen, S, and Coulson, AR: DNA sequencing with chain-terminating inhibitors. Proc Natl Acad Sci USA 74:5463–5467, 1977. 30. Southern, EM: Detection of specific sequences among DNA fragments separated by gel electrophoresis. J Mol Biol 98: 503–517, 1975. 31. Brown, PO, and Botstein, D: Exploring the new world of the genome with DNA microarrays. Nat Genet 21:33–37, 1999. 32. Hashmi, G, et al: A flexible array format for large-scale, rapid blood group DNA typing. Transfusion 45(5):680–688, 2005. 33. Montpetit, A, et al: High-throughput molecular profiling of blood donors for minor red blood cell and platelet antigens. Transfusion 46(5):841–848, 2006. 34. Bennett, EP, et al: Genomic cloning of the human histo-blood group ABO locus. Biochem Biophys Res Commun 206(1): 318–325, 1995. 35. Lyondagger, E, Millsondagger, A, Phan, T, and Wittwer, CT: Detection and Identification of base alterations within the region of factor V Leiden by fluorescent melting curves. Mol Diagn 3(4):203–209, 1998.

2682_Ch04_077-100 22/05/12 11:40 AM Page 100

100

PART I

Fundamental Concepts

36. U.S. Food and Drug Administration: Complete list of donor screening assays for infectious agents and HIV diagnostic assays. Available at www.fda.gov/cber/products/testkits.htm. 37. Wiedmann, M, Kluwick, S, Walter, M, Fauchald, G, Howe, J, Bronold, M, et al: HIV-1, HCV and HBV seronegative window reduction by the new Roche cobas TaqScreen MPX test in seroconverting donors. J Clin Virol 39(4):282–287, 2007. 38. Glynn, SA, Kleinman, SH, Wright, DJ, and Busch, MP: International application of the incidence rate/window period model. Transfusion 42:966–972, 2002. 39. Dodd, RY, Notari, EP, Stramer, S: Current prevalence and incidence of infectious disease markers and estimated window period risk in the American Red Cross blood donor population Transfusion 42:975–979, 2002. 40. Kohler, G, and Milstein, C: Continuous cultures of fused cells secreting antibody of predefined specificity. Nature 256: 495–497, 1975. 41. Venter, JC, et al: The sequence of the human genome. Science 291:1304–1351, 2001. 42. National Center for Biotechnology Information (NCBI) website: www.ncbi.nlm.nih.gov. 43. Capecchi, MR: Altering the genome by homologous recombination. Science 244:1288–1292, 1989. 44. Bronson, SK, and Smithies, O: Altering mice by homologous recombination using embryonic stem cells. J Biol Chem 269:27155–27158, 1995. 45. Daniels, GL, et al: Blood group terminology 2004: From the International Society of Blood Transfusion committee on terminology for red cell surface antigens. Vox Sanguinis 87:304–316, 2004.

46. Daniels, GL, et al. International Society of Blood Transfusion Committee on terminology for red cell surface antigens: Cape Town report. Vox Sanguinis 92:250–253, 2007. 47. Daniels GL, et al. International Society of Blood Transfusion Committee on terminology for red blood cell surface antigens: Macao report. Vox Sanguinis 96:153–156, 2009. 48. ISBT/IBGRL website: http://ibgrl.blood.co.uk/. 49. Blumenfeld, OO, and Patnaik, SK. Allelic genes of blood group antigens: A source of human mutations and cSNPs documented in the Blood Group Antigen Gene Mutation Database. Hum Mutat 23(1):8–16, 2004. 50. Reid, ME: Transfusion in the age of molecular diagnostics. Hematology 171–177, 2009. 51. Westhoff, CM: The potential of blood group genotyping for transfusion medicine practice. Immunohematology 24(4): 190–195, 2008. 52. Finning, K, Martin, P, Summers, J, and Daniels, G: Fetal genotyping for the K (Kell) and Rh C, c, and E blood groups on cell-free fetal DNA in maternal plasma. Transfusion 47:2126–2133, 2007. 53. Anstee, DJ: Red cell genotyping and the future of pretransfusion testing. Blood 114:(2), 2009. 54. The dbRBC, Blood Group Antigen Gene Mutation Database. Historical landmarks in the field of study of blood group systems. Available at www.ncbi.nlm.nih.gov/projects/gv/rbc/ xslcgi.fcgi?cmd=bgmut/landmarks.

2682_Ch05_101-118 22/05/12 11:41 AM Page 101

Blood Groups and Serologic Testing

Part II Chapter

5

The Antiglobulin Test Ralph E. B. Green, BAppSc, FAIMLS, MACE and Dwane A. Klostermann, MSTM, MT(ASCP)SBB

Introduction History of the Antiglobulin Test Antihuman Globulin Reagents Polyspecific AHG Monospecific AHG Preparation of AHG Polyspecific AHG Monospecific AHG Antibodies Required in AHG Anti-IgG Anticomplement Use of Polyspecific Versus Monospecific AHG in the IAT Principles of the Antiglobulin Test Direct Antiglobulin Test Principle and Application

DAT Panel Evaluation of a Positive DAT Indirect Antiglobulin Test Factors Affecting the Antiglobulin Test Ratio of Serum to Cells Reaction Medium Temperature Incubation Time Washing of RBCs Saline for Washing Addition of AHG Centrifugation for Reading Sources of Error Modified and Automated Antiglobulin Test Techniques Low Ionic Polybrene Technique

Enzyme-Linked Antiglobulin Test Solid Phase Technology Gel Test Comparison of AHG Methodologies DAT Methods IAT Methods Case Studies Case 5-1 Case 5-2 Summary Chart Review Questions References

OBJECTIVES 1. State the principle of the antiglobulin test. 2. Differentiate monoclonal from polyclonal and monospecific from polyspecific antihuman globulin (AHG) reagents. 3. Describe the preparation of monoclonal and polyclonal AHG reagents. 4. List the antibody requirements for AHG reagents. 5. Explain the use of polyspecific versus monospecific AHG in the indirect antiglobulin test (IAT). 6. List the advantages and disadvantages of anticomplement activity in polyspecific AHG. 7. Compare and contrast the IAT and the direct antiglobulin test (DAT). 8. Explain the principle and applications of red blood cell sensitization. 9. Explain the reasons for the procedural steps in the DAT and IAT. 10. Interpret the results of a DAT and IAT panel. 11. Identify the factors that affect the antiglobulin test. Continued

101

2682_Ch05_101-118 22/05/12 11:41 AM Page 102

102

PART II

Blood Groups and Serologic Testing

OBJECTIVES—cont’d 12. Formulate the steps necessary to resolve errors associated with the performance of the antiglobulin test. 13. Describe the multiple methodologies utilized in AHG testing. 14. State the advantages and disadvantages of various methodologies utilized for DAT and IAT testing based on the needs of the transfusion service department.

Introduction The antihuman globulin test, which is also referred to as the Coombs’ test, is based on the principle that antihuman globulins (AHGs) obtained from immunized nonhuman species bind to human globulins such as IgG or complement, either free in serum or attached to antigens on red blood cells (RBCs). The antihuman globulin test (AGT) is an essential testing methodology when it comes to transfusion medicine; without its use, patients’ well-being would be negatively impacted. There are two major types of blood group antibodies: IgM and IgG. Because of their large pentamer structure, IgM antibodies bind to corresponding antigen and directly agglutinate RBCs suspended in saline. Some IgG antibodies are termed nonagglutinating, or incomplete antibodies, because their monomer structure is too small to directly agglutinate sensitized RBCs (refer back to the ionic cloud concept schematic found in Chapter 3, “Fundamentals of Immunology”). Adding AHG that contains anti-IgG to RBCs sensitized with IgG antibodies allows for hemagglutination of these sensitized cells. We use an anti-antibody to observe the formation of an Ag/Ab complex that would otherwise go undetected. Some blood group antibodies have the ability to bind complement to the RBC membrane. In such cases, an anticomplement component can be added to the AHG reagent, rendering it polyspecific. Antiglobulin tests detect IgG or complement-sensitized RBCs.

History of the Antiglobulin Test Before the antiglobulin test was developed, only IgM antibodies were detected. The introduction of the AGT permitted the detection of nonagglutinating IgG antibodies and led to the discovery and characterization of many new blood group systems. In 1945, Coombs and associates1 described the use of the antiglobulin test for the detection of weak and nonagglutinating Rh antibodies in serum. In 1946, Coombs and coworkers2 described the use of AHG to detect in vivo sensitization of the RBCs (later called the direct antiglobulin test [DAT]) of babies suffering from hemolytic disease of the newborn (HDN). Although the test was initially of great value in the investigation of Rh HDN, its versatility for detecting other IgG blood group antibodies soon became evident. The first of the Kell blood group system antibodies3 and the associated antigen were reported only weeks after Coombs had described the test. Although Coombs and associates1 were instrumental in introducing the antiglobulin test

to blood group serology, the principle of the test had in fact been described by Moreschi4 in 1908. Moreschi’s studies used rabbit antigoat serum to agglutinate rabbit RBCs that were sensitized with low nonagglutinating doses of goat antirabbit RBC serum. Coombs’ procedure involved the injection of human serum into rabbits to produce antihuman serum (described in detail later in this chapter). After absorption to remove heterospecific antibodies and after dilution to avoid prozone, the AHG serum still retained sufficient antibody activity to permit cross-linking of adjacent RBCs sensitized with IgG antibodies. The cross-linking of sensitized RBCs by AHG produced hemagglutination, indicating that the RBCs had been sensitized by an antibody that had reacted with an antigen present on the cell surface. Early AHG reagents were prepared using a crude globulin fraction as the immunogen. In 1947, Coombs and Mourant demonstrated that the antibody activity that detected Rh antibodies was associated with the anti–gamma globulin fraction in the reagent. In 1951, Dacie5 presented the first indication that there might be another antibody activity present that influenced the final reaction. He observed that different reaction patterns were obtained when dilutions of AHG were used to test cells sensitized with warm as compared with cold antibodies. In 1957, Dacie and coworkers6 published data showing that the reactivity of AHG to cells sensitized with warm antibodies resulted from anti–gamma globulin activity, whereas anti–nongamma globulin activity was responsible for the activity of cells sensitized by cold antibodies. The nongamma globulin component was shown to be beta globulin and had specificity for complement. Later studies7,8 revealed that the complement activity was a result of C3 and C4. The antiglobulin test can be used to detect RBCs sensitized with IgG alloantibodies, IgG autoantibodies, and complement components. Sensitization can occur either in vivo or in vitro. The use of AHG to detect in vitro sensitization of RBCs is a two-stage technique referred to as the indirect antiglobulin test (IAT). In vivo sensitization is detected by a one-stage procedure called the direct antiglobulin test (DAT). The IAT and DAT still remain the most common procedures performed in blood group serology.9

Antihuman Globulin Reagents Several AHG reagents have been defined by the Food and Drug Administration (FDA) Center for Biologics Evaluation and Research (CBER). These are listed in Table 5–1 and are described in the following paragraphs. Antihuman globulin reagents can be polyspecific or monospecific.

2682_Ch05_101-118 22/05/12 11:41 AM Page 103

Chapter 5 The Antiglobulin Test

103

Table 5–1 Antihuman Globulin Reagents REAGENT

DEFINITION

Polyspecific 1. Rabbit polyclonal

Contains anti-lgG and anti-C3d (may contain other anticomplement and other anti-immunoglobulin antibodies)

2. Rabbit/murine monoclonal blend

Contains a blend of rabbit polyclonal antihuman IgG and murine monoclonal anti-C3b and anti-C3d.

3. Murine monoclonal

Contains murine monoclonal anti-IgG, anti-C3b, and anti-C3d.

Monospecific Anti-IgG 1. Rabbit polyclonal

Contains anti-IgG with no anticomplement activity (not necessarily gamma-chain specific)

2. IgG heavy-chain specific

Contains only antibodies reactive against human gamma chains

3. Monoclonal IgG

Contains murine monoclonal anti-IgG

Anticomplement Rabbit polyclonal 1. Anti-C3d and anti-C3b

Contains only antibodies reactive against the designated complement

2. Anti-C3d, anti-C4b, anti-C4d

Component(s), with no anti-immunoglobulin activity

Murine Monoclonal 1. Anti-C3d

Contains only antibodies reactive against the designated complement

2. Anti-C3b, anti-C3d

Component, with no anti-immunoglobulin activity

Data from Tyler, V (ed): Technical Manual, 12th ed. American Association of Blood Banks, Bethesda, MD, 1996.

Polyspecific AHG Polyspecific AHG reagents contain antibody to human IgG and to the C3d component of human complement. Other anticomplement antibodies, such as anti-C3b, anti-C4b, and anti-C4d, may also be present. Therefore, its use can facilitate agglutination when RBCs have been sensitized with IgG or C3d or both. Commercially prepared polyspecific AHG contains little, if any, activity against IgA and IgM heavy chains. However, the polyspecific mixture may contain antibody activity to kappa and lambda light chains common to all immunoglobulin classes, thus reacting with IgA or IgM molecules.10

Monospecific AHG Monospecific AHG reagents contain only one antibody specificity: either anti-IgG or antibody to specific complement components such as C3b or C3d (i.e., anticomplement). Licensed monospecific AHG reagents in common use are anti-IgG and anti-C3b-C3d.10 Anti-IgG Reagents labeled anti-IgG contain no anticomplement activity. Anti-IgG reagents contain antibodies specific for the FC fragment of the gamma heavy chain of the IgG molecule. If not labeled “gamma heavy chain–specific,” anti-IgG may contain anti–light chain specificity and may therefore react with cells sensitized with IgM, IgA, and IgG.10

Anticomplement Anticomplement reagents, such as anti-C3b, anti-C3d reagents, are reactive against only the designated complement components and contain no activity against human immunoglobulins.10 Monospecific anticomplement reagents are often a blend of monoclonal anti-C3b and monoclonal anti-C3d (see the following sections for descriptions of monoclonal and polyclonal antibody production).

Preparation of AHG The classic method of AHG production involves injecting human serum or purified globulin into laboratory animals such as rabbits. The human globulin behaves as foreign antigen, the rabbit’s immune response is triggered, and an antibody to human globulin is produced. For example, human IgG injected into a rabbit results in anti-IgG production; human complement components injected into a rabbit result in anticomplement. This type of response produces a polyclonal antiglobulin serum. Polyclonal antibodies are a mixture of antibodies from different plasma cell clones. The resulting polyclonal antibodies recognize different antigenic determinants (epitopes), or the same portion of the antigen but with different affinities. Hybridoma technology can be used to produce monoclonal antiglobulin serum. Monoclonal antibodies are derived from one clone of plasma cells and recognize a single epitope.

2682_Ch05_101-118 22/05/12 11:41 AM Page 104

104

PART II

Blood Groups and Serologic Testing

Polyspecific AHG Polyspecific AHG can be made using polyclonal or monoclonal antibodies. The two types of antibody production processes are very different from one another, yielding two very different advantages and disadvantages in their usage. Polyclonal AHG Production Polyclonal AHG is usually prepared in rabbits, although when large volumes of antibody are required, sheep or goats may be used. In contrast with the early production methods, in which a crude globulin fraction of serum was used as the immunogen, modern production commences with the purification of the immunogen from a large pool of normal sera. Conventional polyspecific antiglobulin reagents are produced by immunizing one colony of rabbits with human immunoglobulin (IgG) antigen and another colony with human C3 antigen. Because of the heterogeneity of IgG molecules, using serum from many donors to prepare the pooled IgG antigen to immunize the rabbits and the pooling of antiIgG from many immunized rabbits is essential in producing polyclonal reagents for routine use that are capable of detecting the many different IgG antibodies. This is an advantage of using anti-IgG of polyclonal origin for antiglobulin serum.11 Both colonies of animals are hyperimmunized to produce high-titer, high-avidity IgG antibodies. Blood specimens are drawn from the immunized animals, and if the antibody potency and specificity meet predetermined specifications, the animals are bled for a production batch of reagent. Separate blends of the anti-IgG and anticomplement antibodies are made, and each pool is then absorbed with A1, B, and O cells to remove heterospecific antibodies. The preparation of polyclonal AHG is diagrammed in Figure 5–1. The total antibody content of each pool is determined, and the potency of the pools is analyzed to calculate the optimum antibody dilution for use. Block titrations for anti-IgG pools are performed by reacting dilutions of each antibody against cells sensitized with different amounts of IgG. This is a critical step in the manufacturing process because excess antibody, especially with anti-IgG, may lead to prozoning and, hence, false-negative test results. Because it is not possible to coat cells with measured amounts of complement, the potency of anti-C3 pools is measured using at least two examples each of a C3b- and C3d-coated cell. Both anti-C3b (C3c) and anti-C3d are present in the polyclonal anti-C3 pool. The level of anti-C3d is critical in keeping false-positive tests to a minimum yet also detecting clinically significant amounts of RBC-bound C3d. Additionally, if the dilution of the anti-C3 pool is determined on the basis of the amount of anti-C3d present, the level of anti-C3b (C3c) varies. The inability to determine the potency of anti-C3b and anti-C3d individually is one of the difficulties with polyclonal reagents that can be avoided with monoclonal products.11 Monoclonal AHG Production The monoclonal antibody technique devised by Kohler and Milstein12 has been used to produce AHG and has proved particularly useful in producing high-titer antibodies with welldefined specificities to IgG and to the fragments of C3.13–15

Conventional Method Polyclonal Antihuman Globulin IgG

Complement Rabbit is injected with pooled donor antigen

Antibody collected from multiple rabbits and purified Monospecific Polyclonal Anti-IgG

Monospecific Polyclonal Anti-C3b,d

AHG Polyspecific Polyclonal Blend Figure 5–1. Preparation of polyclonal AHG reagents. Pooled donor antigen allows for a broader spectrum of reactivity, but the source of antibody is limited to the life span of the inoculated animal. Polyspecific antihuman globulin may be manufactured by combining polyclonal anti-IgG with either polyclonal or monoclonal anticomplement components.

Monoclonal antibody production begins with the immunization of laboratory animals, usually mice, with purified human globulin. After a suitable immune response, mouse spleen cells containing antibody-secreting lymphocytes are fused with myeloma cells. The resulting “hybridomas” are screened for antibodies with the required specificity and affinity. The antibody-secreting clones may then be propagated in tissue culture or by inoculation into mice, in which case the antibody is collected as ascites. Because the clonal line produces a single antibody, there is no need for absorption to remove heterospecific antibodies. All antibody molecules produced by a clone of hybridoma cells are identical in terms of antibody structure and antigen specificity. This has advantages and disadvantages in AHG production. Once an antibody-secreting clone of cells has been established, antibody with the same specificity and reaction characteristics will be available indefinitely. This allows the production of a consistently pure and uncontaminated AHG reagent. The disadvantage is that all antibodies produced by a clone of cells recognize a single epitope present on an antigen. For antigens composed of multiple epitopes such as IgG, several different monoclonal antibodies reacting with different epitopes may need to be blended, or a monoclonal antibody specificity for an epitope on all variants of a particular antigen may need to

2682_Ch05_101-118 22/05/12 11:41 AM Page 105

Chapter 5 The Antiglobulin Test

be selected to ensure that all different expressions of the antigen are detected. Monoclonal antibodies to human complement components anti-C3b and anti-C3d may be blended with polyclonal anti-IgG from rabbits to achieve potent reagents that give fewer false-positive reactions as a result of anticomplement. Immucor manufactures AHG reagents from an entirely monoclonal source. The anti-IgG component is produced by exposing mice to RBCs coated with IgG. The resulting monoclonal anti-IgG reacts with the CH3 region of the gamma chain of IgG subclasses 1, 2, and 3. The antibody does not react with human antibodies of subclass IgG4, but these are not considered to be clinically significant. Blending the monoclonal anti-IgG with a monoclonal anti-C3b and monoclonal anti-C3d results in a polyspecific AHG reagent. The preparation of monoclonal AHG is diagrammed in Figure 5–2. Before the AHG is available for purchase, manufacturers must subject their reagents to an evaluation procedure, and the results must be submitted to the FDA for approval. Whether produced by the polyclonal or monoclonal technique, the final polyspecific product is one that contains both anti-IgG and anticomplement activity at the correct potency for immediate use. The reagent also contains buffers, stabilizers, and bacteriostatic agents and may be dyed green for identification.

105

Monospecific AHG Monospecific AHG production process is similar to that described above for polyspecific AHG; however, it contains only one antibody specificity. Monospecific anti-IgG is produced as a monoclonal, polyclonal, or blended formula.

Antibodies Required in AHG We have already discussed the need to use both polyspecific and monospecific AHG reagents. However, the reader should be aware of the specific requirements for the subclasses and components of IgG and complement required in the reagent.

Anti-IgG AHG must contain antibody activity to nonagglutinating blood group antibodies. The majority of these antibodies are a mixture of IgG1 and IgG3 subclasses. Rarely, nonagglutinating IgM antibodies may be found; however, they have always been shown to fix complement and may be detected by anticomplement.16 IgA antibodies with Rh specificity have been reported, but IgG antibody activity has always been present as well. The only RBC alloantibodies that have been reported as being solely IgA have been examples of anti-Pr,17 and those antibodies were agglutinating. IgA autoantibodies have been reported, although very rarely.18

Figure 5–2. Preparation of monoclonal AHG reagents. The production of antibody is longer lasting than the polyclonal source, as the hybridoma can live indefinitely. A monoclonal blend may be manufactured by blending monoclonal anti-C3b, monoclonal anti-C3d, and monoclonal anti-IgG. Monospecific antihuman globulin reagents can be manufactured by conventional or hybridoma technology.

Hybridoma Technology Monoclonal Antihuman Globulin IgG

Complement Mouse is injected with purified human antigen

Antibody-producing lymphocytes collected from spleen

Myeloma cell

Myeloma cell Fusion with myeloma cell to form hybridoma

Monoclonal Anti-C3b,d,g

Clones grown in tissue culture to yield monoclonal antibodies

AHG Polyspecific Monoclonal Blend

Monoclonal Anti-IgG

2682_Ch05_101-118 22/05/12 11:41 AM Page 106

106

PART II

Blood Groups and Serologic Testing

Therefore, anti-IgG activity must be present in the AHG reagent. Anti-IgM and anti-IgA activity may be present, but neither is essential. The presence of anti–light chain activity allows detection of all immunoglobulin classes.

Anticomplement Some antibodies “fix” complement components to the RBC membrane after complexing of the antibody with its corresponding antigen. These antibodies are listed in Table 5–2 and are described in more detail in Chapters 6 through 9. The terms most, some, and rare in the table refer to antibodies that bind complement the vast majority of the time, that show variability in their ability to bind complement, and that rarely bind complement, respectively. These membranebound complement components can be detected by the anticomplement activity in AHG. As a result of studies published during the 1960s19–22 indicating the need for anticomplement activity in AHG to allow the IAT to detect antibodies, polyspecific reagent was introduced. Evidence was also presented showing that the presence of anticomplement activity would enhance the reactions of clinically significant antibodies (e.g., anti-Fya and anti-K).19 During complement activation, C3 and C4 are split into two components. C3b and C4b bind to the RBC membrane, whereas C3a and C4a pass into the fluid phase. Further degradation of membrane-bound C3b and C4b occurs by removing C3c and C4c to leave C3d and C4d firmly attached to the RBC membrane.23–25 The ISBT/ICSH Joint Working Party26 considered anti-C3c to be the most important anticomplement component because of its limited capacity to cause nonspecific reactions. However, when RBCs are incubated with serum for

Table 5–2 Antibodies Capable of Binding Complement MOST

SOME

RARE

ABO

Xga

D

Lea

LKE

P1

Leb

Lan

Lua

Jka

Lub

Jkb

Kell

Sc1

Fya

Co3

Fyb

Ge2

Coa

Ge3

Cob

Ii

Dia

P

S

PP1Pk

S

Vel

Yta

longer than 15 minutes, the number of C3c determinants falls rapidly because C3c is split off the C3bi molecule. This finding further supports the use of anti-C3d in international reference reagents by the Joint Working Party. The final degradation step has been shown to occur in vivo27 and is a common occurrence in both warm and cold autoimmune hemolytic anemias. Engelfriet and others28 have also shown that degradation of C3b to C3d can occur in vitro, providing that the incubation period is greater than 1 hour. In 1976, Garratty and Petz29 confirmed the need for anti-C3d activity in AHG for use in the DAT. They also confirmed Engelfriet’s observation that, given sufficient time, cell-bound C3b could be degraded to C3d in vitro. Refer back to Table 5–1 for a detailed listing of all AHG reagents’ components.

Use of Polyspecific Versus Monospecific AHG in the IAT As previously stated, polyspecific AHG contains both antiIgG activity and anti-C3 activity. There is considerable debate among blood bankers over the use of monospecific anti-IgG versus polyspecific AHG for routine antibody detection and pretransfusion testing. Because most clinically significant antibodies detected during antibody screening are IgG, the most important function of polyspecific AHG is the detection of IgG antibodies. There have been numerous reports of clinically significant RBC alloantibodies that were undetectable with monospecific anti-IgG but were detected with the anticomplement component of AHG.30 Unfortunately, polyspecific AHG has also been associated with unwanted positive reactions that are not caused by clinically significant antibodies. To investigate these variables, Petz and coworkers31 examined 39,436 sera comparing monospecific anti-IgG with polyspecific AHG. They also compared the albumin technique with low ionic strength solutions (LISS)-suspended RBCs. Four Jka antibodies were detected only with polyspecific anti-IgG using albumin or LISS-suspended RBCs. An additional anti-Jka was detected only with polyspecific AHG when using LISS but not with albumin. Also, five antibodies of anti-Kell, anti-Jka, and Fya specificities were detected when using LISS, but not albumin, with both polyspecific AHG and anti-IgG. Their results concluded that some clinically significant antibodies are detected with the anticomplement component of AHG but not with anti-IgG. This is especially true for anti-Jka, a complement-binding IgG antibody often associated with delayed hemolytic transfusion reactions. Petz and others31 also determined the number of falsepositive reactions obtained when using polyspecific AHG versus anti-IgG with LISS and albumin. False-positive reactions were defined as those caused by antibodies with no definable specificity or by antibodies considered to be clinically insignificant because of optimum reactivity at cold temperatures (anti-I, anti-H, anti-P1, anti-M). Of the unwanted positive reactions, 93% were caused by C3 on the cells. The authors emphasize that, if the first step in evaluating a weakly positive AHG reaction is to repeat using the prewarmed technique, although not recommended, about 60% of the false-positive weak reactions become negative.

2682_Ch05_101-118 22/05/12 11:41 AM Page 107

Chapter 5 The Antiglobulin Test

In a 3-year study, Howard and associates32 found eight patients whose antibodies were detected primarily or solely by AHG containing anticomplement activity. Seven of these antibodies had anti-Jka or anti-Jkb specificity. Some of them could be detected using homozygous Jka or Jkb cells and an AHG containing only anti-IgG activity. Two of the anti-Jka antibodies were associated with delayed hemolytic transfusion reactions. The complement-only Kidd antibodies represented 23% of all Kidd antibodies detected during the study. The authors concluded that they would continue to use polyspecific AHG reagent for routine compatibility testing. In summary, one must balance the advantage of detecting clinically significant complement-only antibodies with the disadvantages resulting from using antiglobulin serum containing anticomplement activity.30 Deciding to use the AHG reagent for indirect tests is the prerogative of the individual blood bank. Many blood banks have begun using monospecific anti-IgG for routine pretransfusion testing, citing cost containment measures necessitated by the high number of repeats versus the rarity of complement-only detected antibodies such as anti-Jka. Milam33 states that rare clinical transfusion intolerance, when using monospecific anti-IgG over polyspecific AHG reagents to screen for unexpected antibodies and to test for blood group compatibility, offers reliability without interference from common and clinically insignificant IgM-complement fixing antibodies.

107

Principle and Application The direct antiglobulin test (DAT) detects in vivo sensitization of RBCs with IgG or complement components. Clinical conditions that can result in in vivo coating of RBCs with antibody or complement are: • Hemolytic disease of the newborn (HDN) • Hemolytic transfusion reaction (HTR) • Autoimmune and drug-induced hemolytic anemia (AIHA) Table 5–3 lists the clinical application and in vivo sensitization detected for each situation. The DAT is not a required test in routine pretransfusion protocols. Eder34 tested the clinical utility of the DAT at a large tertiary care hospital in Philadelphia. A retrospective study was performed from 1999 to 2002. DATs with anti-IgG were performed on 15,662 pretransfusion patient samples; 15% were positive. Subsequent eluate testing revealed 76% were nonreactive, 9% were pan reactive, and 12% passively acquired ABO or D antibodies. Only one case demonstrated an RBC antibody in the eluate that was not detected in the serum, concluding that even in a tertiary care setting, the routine DAT is inefficient, yielding a positive predictive value of 0.16%. Judd and coworkers revealed similar findings on 65,049 blood samples in a 29-month period, where only 5.5% of samples resulted in a positive DAT.35

DAT Panel

Principles of the Antiglobulin Test The antiglobulin test is based on the following simple principles:10 • Antibody molecules and complement components are globulins. • Injecting an animal with human globulin stimulates the animal to produce antibody to the foreign protein (i.e., AHG). Serologic tests employ a variety of AHG reagents reactive with various human globulins, including anti-IgG antibody to the C3d component of human complement, and polyspecific reagents that contain both anti-IgG and anti-C3d activity. AHG reacts with human globulin molecules, either bound to RBCs or free in serum. Washed RBCs coated with human globulin are agglutinated by AHG. The complete procedures for the direct and indirect antihuman globulin tests can be found in Procedures 5-1 and 5-2 on the textbook’s companion website. Figure 5–3 illustrates in vitro sensitization detected in the IAT and in vivo sensitization detected by the DAT.

Direct Antiglobulin Test Described above are the overall principles of the antiglobulin test. Figure 5–3 depicts two variations of the AGT, the DAT and the IAT. The following section details the DAT’s principle, application, construct, and evaluation.

Initial DATs include testing one drop of a 3% to 5% suspension of washed RBCs with polyspecific (anti-IgG, anti-C3d) reagent (please refer to the DAT procedure on DavisPlus website). Positive results are monitored by a DAT panel using monospecific anti-IgG and anti-C3d to determine the specific type of protein sensitizing the cell. In an effort to save valuable tech time, some institutions run polyspecific and monospecific reagents at one time as well as a saline control. The saline control serves to detect spontaneous agglutination of cells or reactions occurring without the addition of AHG reagents. In warm AIHA, including drug-induced hemolytic anemia, the RBCs may be coated with IgG or C3d, or both. Patterns of reactivity and the type of protein sensitization in AIHA are summarized in Table 5–4. In a transfusion reaction workup, the DAT may demonstrate IgG or C3d, or both, depending on the nature and specificity of the recipient’s antibody. In the investigation of HDN, testing for complement proteins is not necessary inasmuch as the protein sensitizing the newborn RBCs is

Table 5–3 Direct Antiglobulin Test CLINICAL APPLICATION

IN VIVO SENSITIZATION

HDN

Maternal antibody coating fetal RBCs

HTR

Recipient antibody coating donor RBCs

AIHA

Autoantibody coating individual’s RBCs

2682_Ch05_101-118 22/05/12 11:41 AM Page 108

108

PART II

Blood Groups and Serologic Testing

Figure 5–3. The antihuman globulin (AHG) test. (A) Indirect AHG (IAT), with sensitization occurring in vitro, looking for unknown antibody in the patient’s serum/plasma. (Note: If the IAT was identifying RBC antigens, the RBCs would be from the patient and the antibody would be the known reagent). (B) Direct AHG (DAT) with sensitization already occurring in vivo. (Note: The polyspecific AHG reagent is a mixture of anti-IgG and anti-C3d.)

presumed to be maternal IgG. Problems can arise in accurate D typing in the case of a newborn with a positive DAT. If the DAT is positive due to IgG and the immediate spin for D typing is negative, a test for weak D cannot be performed. The same is true for a patient with AIHA due to a warm IgG antibody coating the patient cells. The antibody must be removed from the RBCs for accurate phenotyping. Other techniques can be used to remove antibody from the patient’s RBCs. These include chloroquine diphosphate, EDTAglycine, and murine monoclonal antibodies.

Evaluation of a Positive DAT Clinical consideration should dictate the extent to which a positive DAT is evaluated. Interpreting the significance of a positive DAT requires knowledge of the patient’s diagnosis, drug therapy, and recent transfusion history. A

Table 5–4 DAT Panel: Patterns of Reactivity in Autoimmune Hemolytic Anemia* ANTI-IgG

ANTI-C3d

TYPE OF AIHA

+

+

WAIHA

+

WAIHA

+

CAS; PCH, WAIHA

+

+

Mixed-type AIHA (cold and warm)

Data from Roback, JD, Combs, MR, Grossman, BJ, and Hillyer, CD (eds): Technical Manual, 16th ed. AABB, Bethesda, MD, 2008. *The DAT with monospecific antiglobulin reagents is helpful in classifying AIHAs. Other procedures and studies are necessary to diagnose and characterize which form of autoimmune disease is present. CAS = cold agglutinin syndrome; PCH = paroxysmal cold hemoglobinuria; WAIHA = warm autoimmune hemolytic anemia

2682_Ch05_101-118 22/05/12 11:41 AM Page 109

Chapter 5 The Antiglobulin Test

positive DAT may occur without clinical manifestations of immune-mediated hemolysis. Table 5–5 outlines the in vivo phenomena that may be associated with a positive DAT. The AABB Technical Manual states that “a positive DAT alone is not diagnostic. The interpretation of the significance of this positive result requires knowledge of the patient’s diagnosis; recent drug, pregnancy, and transfusion history; and information on the presence of acquired or unexplained hemolytic anemia.”36 Answering the following questions before investigating a positive DAT for patients other than neonates will help determine what further testing is appropriate: • Is there evidence of in vivo hemolysis? • Has the patient been transfused recently? If so, did the patient receive blood products or components containing ABO-incompatible plasma? • Does the patient’s serum contain unexpected antibodies? • Is the patient receiving any drugs? • Is the patient receiving antilymphocyte globulin or antithymocyte globulin?

109

• Is the patient receiving intravenous immune globulin (IVIG) or intravenous Rh immune globulin (IV RhIG)? • Has the patient received a marrow or other organ transplant?

Indirect Antiglobulin Test The IAT is performed to determine in vitro sensitization of RBCs and is used in the following situations: • Detection of incomplete (nonagglutinating) antibodies to potential donor RBCs (compatibility testing) or to screening cells (antibody screen) in serum • Determination of RBC phenotype using known antisera (e.g., Kell typing, weak D testing) • Titration of incomplete antibodies Table 5–6 lists the IATs and the in vitro sensitization detected for each application. For in vitro antigen-antibody reactions, the IAT tasks are listed and explained in Table 5–7.

Table 5–5 In Vivo Phenomena Associated With a Positive DAT CONDITION

CAUSE

1. Recipient alloantibody and donor antigen

Alloantibodies in the recipient of a recent transfusion that react with antigen on donor RBC

2. Donor antibody and recipient antigen

Antibodies present in donor plasma that react with antigen on a transfusion recipient’s RBCs

1. Type I (hapten-dependent Ab)

Drug binds covalently to membrane proteins and stimulates hapten-dependent Ab

2. Type II (autoantibody)

Drug induces autoantibody specific for RBC membrane proteins through unknown mechanism; Ab reacts with normal RBCs in the absence of drug.

3. Type III (drug-dependent Ab)

Drug induces Ab that binds to RBC only when drug is present in soluble form, unknown mech; Ab reacts with normal RBCs when soluble drug is present.

1. WAIHA (IgG and/or C3)

Autoantibody reacts with patient’s RBCs in vivo.

2. CAS (C3)

Cold-reactive IgM autoagglutinin binds to RBCs in peripheral circulation (32°C). IgM binds complement as RBCs return to warmer parts of circulation; IgM dissociates, leaving RBCs coated only with complement.

3. PCH (IgG)

The IgG autoantibody reacts with RBCs in colder parts of body, causes complement to be bound irreversibly to RBCs, and then elutes at warmer temperature.

Hemolytic disease of newborn

1. Maternal alloantibody crosses placenta (IgG)

Maternal (IgG) alloantibody, specific for fetal antigen, coats fetal RBCs. DAT is reactive with anti-IgG.

Miscellaneous

1. Absorbed proteins; administration of equine preparations of antilymphocyte globulin and antithymocyte globulin

Heterophile antibodies that are present in ALG or ATG coat recipient’s RBCs. High levels of protein causing red cells to spontaneously agglutinate.

2. Administration of high-dose IV gamma globulin and hypergammaglobulinemia

Non-antibody-mediated binding of immunoglobulin to RBCs in patients with hypergammaglobulinemia

Transfusion

Drug induced

Autoimmune hemolytic anemia

Modified from Roback, JD, Combs, MR, Grossman, BJ, and Hillyer, CD (eds): Technical Manual, 16th ed. AABB, Bethesda, MD, 2008. AIHA = autoimmune hemolytic anemia; CAS = cold agglutinin syndrome; PCH = paroxysmal cold hemoglobinuria.

2682_Ch05_101-118 22/05/12 11:41 AM Page 110

110

PART II

Blood Groups and Serologic Testing

APPLICATION

TESTS

IN VITRO SENSITIZATION

Antibody detection

Compatibility testing

Recipient antibody reacting with donor cells

• • • • • •

Antibody screening

Antibody reacting with screening cells

Ratio of Serum to Cells

Antibody identification

Antibody panel

Antibody reacting with panel cells

Antibody titration

Rh antibody titer

Antibody and selected Rh cells

RBC phenotype

RBC antigen detection (ex: weak D, K, Fy)

Specific antisera + RBCs to detect antigen

Table 5–6 Indirect Antiglobulin Test

The DAT does not require the incubation phase because of the antigen-antibody complexes formed in vivo.

Factors Affecting the Antiglobulin Test The DAT can detect a level of 100 to 500 IgG molecules per RBC and 400 to 1,100 molecules of C3d per RBC.28 For the IAT, there must be between 100 and 200 IgG or C3 molecules on the cell to obtain a positive reaction. The number of IgG molecules that sensitize an RBC and the rate at which sensitization occurs can be influenced by several factors, including: • Ratio of serum to cells • Reaction medium

Table 5–7 Tasks and Purposes of the Indirect Antiglobulin Test TASK

PURPOSE

Incubate RBCs with antisera

Allows time for antibody molecule attachment to RBC antigen

Perform a minimum of three saline washes

Removes free globulin molecules

Add antiglobulin reagent

Forms RBC agglutinates (RBC Ag + Ab + anti-IgG)

Centrifuge

Accelerates agglutination by bringing cells closer together

Examine for agglutination

Interprets test as positive or negative

Grade agglutination reactions

Determines the strength of reaction

Add antibody-coated RBCs to negative reactions

Checks for neutralization of antisera by free globulin molecules (Coombs’ control cells are D-positive RBCs coated with anti-D)

Temperature Incubation time Washing of RBCs Saline for washing Addition of AHG Centrifugation for reading

Increasing the ratio of serum to cells increases the sensitivity of the test system. Generally, a minimum ratio of 40:1 should be the target, and this can be achieved by using 2 drops of serum and 1 drop of a 5% volume of solute per volume of solution (v/v) suspension of cells.34 When using cells suspended in saline, it is often advantageous to increase the ratio of serum to cells in an effort to detect weak antibodies (e.g., 4 drops of serum with 1 drop of a 3% [v/v] cell suspension will give a ratio of 133:1).

Reaction Medium Reaction mediums include albumin, LISS, and polyethylene glycol. Albumin The macromolecules of albumin allow antibody-coated cells to come into closer contact with each other so that aggregation occurs. In 1965, Stroup and MacIlroy37 reported on the creased sensitivity of the IAT if albumin was incorporated into the reaction medium. Their reaction mixture, consisting of 2 drops of serum, 2 drops of 22% (w/v) bovine albumin, and 1 drop of 3% to 5% (v/v) cells, was shown to provide the same sensitivity at 30 minutes of incubation as a 60-minute salineonly test. The use of albumin does not seem to provide any advantage over LISS techniques and adds to the cost of the test.37 Petz and coworkers31 also showed that an albumin technique may miss several clinically significant antibodies. Therefore, it is rarely, if ever, used as an IAT media for routine tests. Low Ionic Strength Solutions Low ionic strength solutions (LISS) enhance antibody uptake and allow incubation times to be decreased—from 30 to 60 minutes to 10 to 15 minutes—by reducing the zeta potential surrounding an RBC. Some LISS also contain macromolecular substances. The LISS technique, introduced by Low and Messeter,38 has critical requirements with respect to the serum-to-cell ratio. Moore and Mollison39 showed that optimum reaction conditions were obtained using 2 drops of serum and 2 drops of a 3% (v/v) suspension of cells in LISS. Increasing the serum-to-cell ratio increased the ionic strength of the reaction mixture, leading to a decrease in sensitivity and counteracting the shortened incubation time of the test. A LISS medium may be achieved by either suspending RBCs in LISS or using a LISS additive reagent, with the latter being more common practice. Polyethylene Glycol Polyethylene glycol (PEG) is a water-soluble linear polymer and is used as an additive to increase antibody uptake. Its

2682_Ch05_101-118 22/05/12 11:41 AM Page 111

Chapter 5 The Antiglobulin Test

action is to remove water molecules surrounding the RBC (the water of hydration theory), thereby effectively concentrating antibody. Anti-IgG is the AHG reagent of choice with PEG testing to avoid false-positive reactions.10 Because PEG may cause aggregation of RBCs, reading for agglutination following 37°C incubation in the IAT is omitted. Several investigators40 compared the performance of PEG as an enhancement media with that of LISS. Findings indicated that PEG increases the detection of clinically significant antibodies while decreasing detection of clinically insignificant antibodies. Barrett and associates41 reported that as PEG has been used for pretransfusion antibody screening, 6,353 RBC components have been transfused without any reported acute or delayed HTRs.

Temperature The rate of reaction for the majority of IgG antibodies is optimal at 37°C; therefore, this is the usual incubation temperature for the IAT. This is also the optimum temperature for complement activation.

Incubation Time For cells suspended in saline, incubation times may vary between 30 and 120 minutes. The majority of clinically significant antibodies can be detected after 30 minutes of incubation, and extended incubation times are usually not necessary. If a LISS or PEG technique is being used,38,39 incubation times may be shortened to 10 to 15 minutes. With these shortened times, it is essential that tubes be incubated at a temperature of 37°C. Extended incubation (i.e., up to 40 minutes) in the LISS technique has been shown to cause antibody to elute from the RBCs, decreasing the sensitivity of the test.42 However, this could not be confirmed by Voak and coworkers.43

Washing of RBCs When both the DAT and IAT are performed, RBCs must be saline-washed a minimum of three times before adding AHG reagent. Washing the RBCs removes free unbound serum globulins. Inadequate washing may result in a falsenegative reaction because of neutralization of the AHG reagent by residual unbound serum globulins. The washing phase of a DAT and IAT becomes one of the most important steps in testing. The wash phase can be controlled using check cells, or group O cells sensitized with IgG. Washing should be performed immediately after being removed from the incubator and in as short a time as possible to minimize the elution of low-affinity antibodies. The cell pellet should be completely resuspended before adding the next saline wash. All saline should be discarded after the final wash, because residual saline dilutes the AHG reagent and therefore decreases the sensitivity of the test. Centrifugation at each wash should be sufficient to provide a firm cell pellet and therefore minimize the possible loss of cells with each discard of saline.

111

Saline for Washing Ideally, the saline used for washing should be fresh or buffered to a pH of 7.2 to 7.4. Saline stored for long periods in plastic containers has been shown to decrease in pH, which may increase the rate of antibody elution during the washing process, yielding a false-negative result.44 One of the contributors (dk) has seen this phenomenon occur in working student labs when expiration dates are ignored to conserve resources. Changes in pH may have important implications when monoclonal AHG is used, inasmuch as monoclonal antibodies have been shown to have narrow pH ranges for optimum reactivity. Significant levels of bacterial contamination in saline have been reported;45 this situation can contribute to false-positive results.

Addition of AHG AHG should be added to the cells immediately after washing to minimize the chance of antibody eluting from the cell and subsequently neutralizing the AHG reagent. The volume of AHG added should be as indicated by the manufacturers. However, Voak and associates46 have shown that adding two volumes of AHG may overcome washing problems when low levels of serum contamination remain. These authors indicated that the neutralization of AHG is a problem only with free IgG left in serum following inadequate saline washings and not with residual serum complement components. The complement fragments free in serum are not the same as the complement fragments bound to RBCs, and therefore residual serum does not contain C3b and C3d to neutralize the anti-C3b and anti-C3d in AHG reagent.

Centrifugation for Reading Centrifugation of the cell pellet for reading of hemagglutination along with the method used for resuspending the cells is a crucial step in the technique. The CBER-recommended method for the evaluation of AHG uses 1,000 relative centrifugal forces (RCFs) for 20 seconds, although the technique described in this chapter suggests 500 RCFs for 15 to 20 seconds. The use of higher RCFs yields more sensitive results; however, depending on how the pellet is resuspended, it may give weak false-positive results because of inadequate resuspension or may give a negative result if resuspension is too vigorous. The optimum centrifugation conditions should be determined for each centrifuge.

Sources of Error Some of the most common sources of error associated with the performance of the AHG test have been outlined in the previous section. Box 5–1 lists reasons for false-negative and false-positive AHG reactions. An anticoagulant such as EDTA should be used to collect blood samples for the DAT to avoid the in vitro complement attachment associated with refrigerated clotted specimens.47 All negative antiglobulin test reactions must be checked by the addition of IgG-sensitized cells. Adding IgG-coated

2682_Ch05_101-118 22/05/12 11:41 AM Page 112

112

PART II

Blood Groups and Serologic Testing

BOX 5–1

Sources of Error in Antihuman Globulin Testing False-Positive Results

False-Negative Results

• Improper specimen (refrigerated, clotted) may cause in vitro complement attachment • Overcentrifugation and overreading • Centrifugation after the incubation phase when PEG or other positively charged polymers are used as an enhancement medium • Bacterial contamination of cells or saline used in washing • Dirty glassware • Presence of fibrin in the test tube may mimic agglutination. • Cells with a positive DAT will yield a positive IAT. • Polyagglutinable cells • Saline contaminated by heavy metals or colloidal silica • Using a serum sample for a DAT (use EDTA, ACD, or CPD anticoagulated blood) • Samples collected in gel separator tubes may have unauthentic complement attachment. • Complement attachment when specimens are collected from infusion lines infusing dextrose solutions • Preservative-dependent antibody directed against reagents

• Inadequate or improper washing of cells • Failure to wash additional times when increased serum volumes are used • Contamination of AHG by extraneous protein (i.e., glove, wrong dropper) • High concentration of IgG paraproteins in test serum • Early dissociation of bound IgG from RBCs due to interruption in testing • Early dissociation of bound IgG from RBCs due to improper testing temperature (i.e., saline or AHG too cold or hot) • AHG reagent nonreactive because of deterioration or neutralization (improper reagent storage) • Excessive heat or repeated freezing and thawing of test serum • Serum nonreactive because of deterioration of complement • AHG reagent, test serum, or enhancement medium not added • Undercentrifuged or overcentrifuged • Cell suspension either too weak or too heavy • Serum:cell ratios are not ideal • Rare antibodies are present that are only detectable with polyspecific AHG and when active complement is present. • Low pH of saline • Inadequate incubation conditions in the IAT • Poor reading technique

Modified from Roback, JD, Combs, MR, Grossman, BJ, and Hillyer, CD (eds): Technical Manual, 16th ed. AABB, Bethesda, MD, 2008.

RBCs to negative test reactions should demonstrate hemagglutination of these RBCs with the anti-IgG in the AHG reagent. If no hemagglutination follows the addition of IgGcoated RBCs, the test result is invalid and the test must be repeated. The most common technical errors that result in failure to demonstrate hemagglutination after the addition of IgG-coated RBCs are inadequate washing, nonreactive AHG reagent, and failure to add AHG reagent. While most blood banks do not check monospecific anti-C3d reactivity with the addition of C3d-coated RBCs to negative reactions, these cells are available and may also be produced in-house.47

Modified and Automated Antiglobulin Test Techniques Modifications to the antiglobulin test technique (LISS, PEG, and albumin) have just been described; however, additional modifications may be used in special circumstances, including the low-iconic polybrene technique, enzyme-linked antiglobulin test, solid phase technology, and gel test.

Low Ionic Polybrene Technique In 1980, Lalezari and Jiang48 reported on the adaptation of the automated low ionic polybrene (LIP) technique for use as a manual procedure. The technique relies on low ionic conditions to rapidly sensitize cells with antibody. Polybrene, a potent rouleaux-forming reagent, is added to allow the sensitized cells to approach each other and permit cross-linking

by the attached antibody. A high ionic strength solution is then added to reverse the rouleaux; however, if agglutination is present, it will remain. The test can be carried through to an AHG technique if required. If this is performed, a monospecific anti-IgG reagent must be used, because the low ionic conditions cause considerable amounts of C4 and C3 to coat the cells and would give false-positive reactions if a polyspecific reagent were used. The antiglobulin test has also been performed using microplates. Crawford and colleagues49 used microplates for a number of different grouping procedures, including the IAT. Microplate technology is used increasingly in blood group serology, and many techniques are being adapted for it. Redman and associates50 have adapted the LIP technique for use in microplates. Although their report does not include the use of an AHG phase, this additional step could easily be included. It should also be mentioned that polybrene has a low sensitivity to detection of anti-Jka and –Jkb and the Jka antigen.51 Therefore, the potential exists for a clinically significant anti-Kidd antibody to be missed using the polybrene method of enhancement for IAT.

Enzyme-Linked Antiglobulin Test In the enzyme-linked antiglobulin test (ELAT), an RBC suspension is added to a microtiter well and washed with saline. AHG, which has been labeled with an enzyme, is added. The enzyme-labeled AHG will bind to IgG-sensitized

2682_Ch05_101-118 22/05/12 11:41 AM Page 113

Chapter 5 The Antiglobulin Test

RBCs. Excess antibody is removed, and enzyme substrate is added. The amount of color produced is measured spectrophotometrically and is proportional to the amount of antibody present. The optical density is usually measured at 405 nm. The number of IgG molecules per RBC can also be determined from this procedure.

113

For the DAT, 50 µL of a 0.8% RBC suspension in LISS solution (ID-Diluent 2) is added to the top of each microtube of the LISS/Coombs ID cards. The cards are centrifuged at 910 rpm for 10 minutes.55 In the case of a positive reaction, monospecific reagents (anti-IgG, anti-C3d) can be used in the gel test. For a detailed description of this technology, see Chapter 12.

Solid Phase Technology Solid-phase technology may be used for performing antiglobulin tests. Several different techniques have been reported using either test tubes51b or microplates.52,53 With the availability of microplate readers, this modification lends itself to the introduction of semiautomation. Direct and indirect tests can be performed using solid-phase methodology. In the former, antibody is attached to a microplate well, and RBCs are added. If antibody is specific for antigen on RBCs, the bottom of the well will be covered with suspension; if no such specificity occurs, RBCs will settle to the bottom of the well. In the latter, known RBCs are bound to a well that has been treated with glutaraldehyde or poly L-lysine. Test serum is added to RBC-coated wells, and if antibody in serum is specific for antigen on fixed RBCs, a positive reaction occurs as previously described. For a detailed description of this technology, see Chapter 12, “Other Technologies and Automation.”

Gel Test The gel test is a process that detects RBC antigen-antibody reactions by means of using a chamber filled with polyacrylamide gel. The gel acts as a trap; free unagglutinated RBCs form pellets in the bottom of the tube, whereas agglutinated RBCs are trapped in the tube for hours. Therefore, negative reactions appear as pellets in the bottom of the microtube, and positive reactions are fixed in the gel. There are three different types of gel tests: neutral, specific, and antiglobulin. A neutral gel does not contain any specific reagent and acts only by its property of trapping agglutinates. The main applications of neutral gel tests are antibody screening and identification with enzyme-treated or untreated RBCs and reverse ABO typing. Specific gel tests use a specific reagent incorporated into the gel and are useful for antigen determination. The gel low ionic antiglobulin test (GLIAT) is a valuable application of the gel test and may be used for the IAT or the DAT. AHG reagent is incorporated into the gel. For example, in an IAT gel, 50 µL of a 0.8% RBC suspension is pipetted onto a gel containing AHG, serum is added, and the tube is centrifuged after a period of incubation. At the beginning of centrifugation, the RBCs tend to pass through the gel, but the medium in which they are suspended remains above. This results in separation between the RBCs and the medium without a washing phase. RBCs come in contact with AHG in the upper part of the gel, and the positive and negative reactions are separated. The detection of unexpected antibodies by GLIAT compares favorably with conventional AHG methods and provides a safe, reliable, and easy-to-read AHG test.54

Comparison of AHG Methodologies Transfusion service departments typically work to detect all clinically significant antibodies, both DAT and IAT types, and none of the clinically insignificant antibodies such as warm and cold-reacting autoantibodies. A common question that arises in these departments is which detection method should be employed to reach such goals. This section briefly compares various AHG methods for DAT and IAT testing. Table 5–8 outlines some of the advantages and disadvantages in various AHG testing methodologies.

DAT Methods There have been numerous studies comparing the tube and gel test when performing DATs. The main difference in the two techniques is that the former requires washing, and the latter omits a washing stage, resulting in discrepant results between the two methods. Multiple studies56–60 concluded that a gel technique used for detecting in vivo sensitized RBCs was more sensitive than the conventional tube technique. However, a comparison study using solid-phase methodology for DAT has not been reported. The gel method, although more sensitive, isn’t necessarily more sensitive only to clinically significant antibodies. Blood banks should be aware of the differences in the DAT when using the popular gel test over the tube technique. Additional comparative studies will add to the current body of knowledge.

IAT Methods There has been a downward trend in conventional tube testing technique in AHG testing, with a gain in popularity for gel technology.61 From a timing and sensitivity perspective, the conventional tube test using saline is the least preferred method.61 The most popular tube medium is LISS followed by PEG.62 Although the LISS and PEG methods are more sensitive than the saline tube method, they are the most labor-intense methods requiring the most skilled staff. One advantage they have over gel and solid phase is the lowered cost of required reagents. Bunker and colleagues63 concluded in their study that the PEG IAT method was the most costeffective pretransfusion antibody screening technique when compared to the solid red cell adherence assay. Gel technology’s introduction into the transfusion service department in the last decade has greatly benefitted the trend in laboratories to use generalist bench techs rather than department-focused techs. Gel technology is less laborintensive than conventional tube testing and incorporates standardization both procedurally and in endpoint grading. This standardization cannot be duplicated using tube testing.

2682_Ch05_101-118 22/05/12 11:41 AM Page 114

114

PART II

Blood Groups and Serologic Testing

Table 5–8 Comparison of AHG Methodologies TESTING METHODOLOGY

ADVANTAGES

DISADVANTAGES

Saline-CTT

• No additives • Reduced cost • Avoids reactivity with auto Abs • Ability to assess multiple phases of reactivity

• Long incubation • Least sensitive • Requires highly trained staff • Most procedural steps • Fewer method-dependent Abs detected

LISS-CTT

• Reduced cost • Avoids reactivity with auto Abs • Shortest incubation time • Increased Ab uptake • Most common tube method • Ability to assess multiple phases of reactivity

• Inability to be automated • Requires highly trained staff • Many procedural steps • Fewer method-dependent Abs detected

PEG-CTT

• Reduced cost • Decreased incubation time • Increased Ab uptake • Enhances most Abs • Ability to assess multiple phases of reactivity (not 37°C)

• Requires highly trained staff • Many procedural steps • Detects more unwanted Abs • Inability to be automated • Fewer method-dependent Abs detected

Gel

• More sensitive DAT method • No washing steps • No need for check cells • Stable endpoints • Small test volume • Enhanced anti-D detection • Ability to be automated

• Warm auto Abs enhanced • Mixed-cell agglutination with cold Abs • Increased costs • Increased need for additional instrumentation • Increased chances of detected unwanted Abs • Need to maintain backup method

Solid phase

• No need for check cells • Stable endpoints • Small test volume • Enhanced anti-D • Increased sensitivity for all Abs • Ability to be automated

• Increased sensitivity for all Abs • Detects unwanted Abs • Warm auto Abs enhanced • Increased costs • Increased need for additional instrumentation

Ab = antibody; CTT = conventional tube testing; LISS = low ionic strength saline; PEG = polyethylene glycol

Gel methods for IAT testing have been shown to be more sensitive than saline, LISS, and PEG at detecting passively acquired anti-D in postnatal patients.64 Weisbach and associates65 have also shown that labs using the gel method are more likely to detect weak antibody reactivity than the LISS tube method. An advantage to using the gel technology in a high-volume lab is its ability to operate as an automated system. A few disadvantages to using the gel method are the increased cost of instrumentation and reagents, the need to stay proficient with alternative methods for backup, and the increased likelihood of detecting unwanted autoantibodies. Solid-phase technology can be incorporated as a manual or automated method for use in IAT. Like gel technology, solid-phase technology is more likely to detect weakly reactive antibodies than the LISS tube method.65 However, with a higher sensitivity comes the detection of more nonspecific reactivity.66,67 Thus, introducing additional costs required to investigate positive screening results. Garozzo and colleagues68 showed that the solid-phase method is even more sensitive at detecting the anti-D than the gel method.

Over the coming years, the changes in blood bank technology, along with the changes in emphasis on the importance of crossmatching versus antibody screening, will probably further modify the role of the antiglobulin test. Methoddependent antibodies have been documented repeatedly in AHG method comparison studies. Some antibodies will be detectable using only one specific method of testing and will be negative in all others. However, AHG methods are comparable in regards to sensitivity and specificity. When deciding which method to use in day-to-day operations, it is important to consider time, resources, facilities and staffing, and the cost of overall testing and how these factors will impact patient care. Current research is under way to utilize molecular diagnostic methods, particularly PCR, to identify RBC genotypes in place of the serologic phenotyping AHG methods. At present, however, serologic AHG testing methods remain the most important in the blood bank for detecting clinically significant antibodies to RBCs and RBC antigens and for detecting immune hemolysis.

2682_Ch05_101-118 22/05/12 11:41 AM Page 115

Chapter 5 The Antiglobulin Test

CASE STUDIES Case 5-1 You are working second shift at a Midwestern suburban hospital. Although you were trained in school using gel technology, your lab utilizes the conventional tube testing method using LISS as an enhancement medium, because the medical director refuses to adopt gel as the primary AHG methodology. About an hour before the end of your shift, the phlebotomist brings you a routine type and screen for a patient just admitted to the medical surgical floor. Because you are confident you can finish before your shift ends, you decide to proceed with testing. The patient types as an A-positive. The antibody screen results were negative in all phases of testing. Therefore, check cells were added to all tubes and the reactions after centrifuging were also negative. 1. Can the antibody screen be interpreted as negative? 2. What steps must be taken to resolve the problem? 3. What is the most likely cause for the discrepant results? 4. What are other causes for the results?

115

Case 5-2 A 34-year-old white male is admitted for an exploratory laparotomy. A type and screen is ordered prior to his scheduled surgery. ABO and Rh typing reveal the patient is O-positive, and the blood bank technologist performed an antibody screen using the patient serum and a two-cell screen using gel technology. One of the cells in the antibody screen is weakly reactive, so you proceed with an antibody identification using a ten-cell panel. However, only two cells are weakly reactive (1+) and show no pattern of reactivity. A second panel is run and yields similar results. You decide to run an antibody identification panel using the conventional tube testing method with LISS as your enhancement medium. All reactions are negative using LISS, including the cells that were previously positive. 1. Can the antibody screen be interpreted as negative? 2. Provide an explanation for the observed results. 3. Are there additional tests that should be conducted to complete testing on this patient? If so, which tests should be run?

SUMMARY CHART

 

    

The antiglobulin test is used to detect RBCs sensitized by IgG alloantibodies, IgG autoantibodies, and complement components. AHG reagents containing anti-IgG are needed for the detection of IgG antibodies because the IgG monomeric structure is too small to directly agglutinate sensitized RBCs. Polyspecific AHG sera contain antibodies to human IgG and the C3d component of human complement. Monospecific AHG sera contain only one antibody specificity: either anti-IgG or antibody to anti–C3b-C3d. Classic AHG sera (polyclonal) are prepared by injecting human globulins into rabbits, and an immune stimulus triggers production of antibody to human serum. Hybridoma technology is used to produce monoclonal antiglobulin serum. The DAT detects in vivo sensitization of RBCs with IgG or complement components. Clinical conditions that can result in a positive DAT include HDN, HTR, and AIHA.

     

The IAT detects in vitro sensitization of RBCs and can be applied to compatibility testing, antibody screen, antibody identification, RBC phenotyping, and titration studies. A positive DAT is followed by a DAT panel using monospecific anti-IgG and anti-C3d to determine the specific type of protein sensitizing the RBC. EDTA should be used to collect blood samples for the DAT to avoid in vitro complement attachment associated with refrigerated clotted specimens. There are multiple sources or error that can be introduced into the AHG procedure. LISS, PEG, polybrene, and albumin can all be used as enhancement media for AHG testing, with each having their own advantages and disadvantages. Conventional tube testing, gel technology, enzymelinked technology, and solid-phase testing are available methods to use in AHG testing. Method-dependent antibodies do exist and should be evaluated on a case-by-case basis.

2682_Ch05_101-118 22/05/12 11:41 AM Page 116

116

PART II

Blood Groups and Serologic Testing

Review Questions 1. A principle of the antiglobulin test is: a. IgG and C3d are required for RBC sensitization. b. Human globulin is eluted from RBCs during saline

washings. c. Injection of human globulin into an animal engenders

passive immunity. d. AHG reacts with human globulin molecules bound to

RBCs or free in serum. 2. Polyspecific AHG reagent contains: a. b. c. d.

Anti-IgG. Anti-IgG and anti-IgM. Anti-IgG and anti-C3d. Anti-C3d.

3. Monoclonal anti-C3d is: a. b. c. d.

Derived from one clone of plasma cells. Derived from multiple clones of plasma cells. Derived from immunization of rabbits. Reactive with C3b and C3d.

4. Which of the following is a clinically significant antibody

whose detection has been reported in some instances to be dependent on anticomplement activity in polyspecific AHG? a. Anti-Jka b. Anti-Lea c. Anti-P1 d. Anti-H 5. After the addition of IgG-coated RBCs (check cells) to a

negative AHG reaction during an antibody screen, a negative result is observed. Which of the following is a correct interpretation? a. The antibody screen is negative. b. The antibody screen needs to be repeated. c. The saline washings were adequate. d. Reactive AHG reagent was added. 6. RBCs must be washed in saline at least three times before

the addition of AHG reagent to: a. Wash away any hemolyzed cells b. Remove traces of free serum globulins c. Neutralize any excess AHG reagent d. Increase the antibody binding to antigen

8. False-positive DAT results are most often associated with: a. Use of refrigerated, clotted blood samples in which

complement components coat RBCs in vitro. b. A recipient of a recent transfusion manifesting an

immune response to recently transfused RBCs. c. Presence of heterophile antibodies from administra-

tion of globulin. d. A positive autocontrol caused by polyagglutination.

9. Polyethylene glycol enhances antigen-antibody reactions

by: a. Decreasing zeta potential. b. Concentrating antibody by removing water. c. Increasing antibody affinity for antigen. d. Increasing antibody specificity for antigen. 10. Solid-phase antibody screening is based on: a. b. c. d.

Adherence. Agglutination. Hemolysis. Precipitation.

11. A positive DAT may be found in which of the following

situations? a. A weak D-positive patient b. A patient with anti-K c. HDN d. An incompatible crossmatch 12. What do Coombs’ control cells consist of? a. b. c. d.

Type A-positive cells coated with anti-D Type A-negative cells coated with anti-D Type O-positive cells coated with anti-D Type O-negative cells coated with anti-D

13. Which of the following methods requires the use of

check cells? a. LISS b. Gel c. Solid-phase d. Enzyme-linked 14. Which factor can affect AHG testing, yet is uncontrollable

in the lab? a. Temperature b. Antibody affinity c. Gravitational force in the centrifuge d. Incubation time

7. An in vitro phenomenon associated with a positive

15. If you had the authority to decide which primary AHG

IAT is: a. Maternal antibody coating fetal RBCs b. Patient antibody coating patient RBCs c. Recipient antibody coating transfused donor RBCs d. Identification of alloantibody specificity using a panel of reagent RBCs

methodology to utilize at your lab, which method would you choose based on the knowledge that the majority of the staff are generalists? a. LISS b. Polybrene c. Solid phase or gel d. Enzyme-linked

2682_Ch05_101-118 22/05/12 11:41 AM Page 117

Chapter 5 The Antiglobulin Test

16. A 27-year-old group O mother has just given birth to a

beautiful, group A baby girl. Since the mother has IgG anti-A in her plasma, it is likely that the baby is experiencing some in vivo red cell destruction. Which of the following methods and tests would be most effective at detecting the anti-A on the baby’s RBCs? a. DAT using common tube technique b. DAT using gel c. IAT using common tube technique d. IAT using gel

References 1. Coombs, RRA, et al: A new test for the detection of weak and “incomplete” Rh agglutinins. Br J Exp Pathol 26:255, 1945. 2. Coombs, RRA, et al: In-vivo isosensitisation of red cells in babies with haemolytic disease. Lancet i:264, 1946. 3. Race, RR, and Sanger, R: Blood Groups in Man, 6th ed. Blackwell Scientific, Oxford, 1975, p 283. 4. Moreschi, C: Neue Tatsachen über die Blutkorperchen Agglutinationen. Zentralbl Bakteriol 46:49, 1908. 5. Dacie, JF: Differences in the behaviour of sensitized red cells to agglutination by antiglobulin sera. Lancet ii:954, 1951. 6. Dacie, JV, et al: “Incomplete” cold antibodies: Role of complement in sensitization to antiglobulin serum by potentially haemolytic antibodies. Br J Haematol 3:77, 1957. 7. Harboe, M, et al: Identification of the component of complement participating in the antiglobulin reaction. Immunology 6:412, 1963. 8. Jenkins, GC, et al: Role of C4 in the antiglobulin reaction. Nature 186:482, 1960. 9. Roback, J, Combs, M, Grossman, B, and Hillyer, C: Technical Manual, 16th ed. CD-ROM. American Association of Blood Banks, Bethesda, MD, 2009. 10. Brecher, ME (ed): Technical Manual, 14th ed. American Association of Blood Banks, Bethesda, MD, 2002. 11. Issitt, C: Monoclonal antiglobulin reagents. Dade International Online, 1997. Available at www.dadeinternational.com/hemo/ papers/monoanti.htm. 12. Kohler, G, and Milstein, C: Continuous cultures of fused cells secreting antibody of predefined specificity. Nature 256:495, 1975. 13. Lachman, PJ, et al: Use of monoclonal antibodies to characterize the fragments of C3 that are found on erythrocytes. Vox Sang 45:367, 1983. 14. Holt, PDJ, et al: NBTS/BRIC 8: A monoclonal anti-C3d antibody. Transfusion 25:267, 1985. 15. Voak, D, et al: Monoclonal antibodies—C3 serology. Biotest Bull 1:339, 1983. 16. Mollison, PL: Blood Transfusion in Clinical Medicine, 7th ed. Blackwell Scientific, Oxford, 1983, p 502. 17. Garratty, G, et al: An IgA high titre cold agglutinin with an unusual blood group specificity within the Pr complex. Vox Sang 25:32, 1973. 18. Petz, LD, and Garratty, G: Acquired Immune Hemolytic Anemias. Churchill Livingstone, New York, 1980, p 193. 19. Polley, MJ, and Mollison, PL: The role of complement in the detection of blood group antibodies: Special reference to the antiglobulin test. Transfusion 1:9, 1961. 20. Polley, MJ, et al: The role of 19S gamma-globulin blood group antibodies in the antiglobulin reaction. Br J Haematol 8:149, 1962. 21. Stratton, F, et al: The preparation and uses of antiglobulin reagents with special reference to complement fixing blood group antibodies. Transfusion 2:135, 1962. 22. Stratton, F, et al: Value of gel fixation on Sephadex G-200 in the analysis of blood group antibodies. J Clin Pathol 21:708, 1968.

117

23. Lachman, PJ, and Muller-Eberhard, HJ: The demonstration in human serum of “conglutinogen-activating-factor” and its effect on the third component of complement. J Immunol 100:691, 1968. 24. Muller-Eberhard, HJ: Chemistry and reaction mechanisms of complement. Adv Immunol 8:1, 1968. 25. Cooper, NR: Isolation and analysis of mechanisms of action of an inactivator of C4b in normal human serum. J Exp Med 141:890, 1975. 26. Case, J, et al: International reference reagents: Antihuman globulin, an ISBT/ICSH Joint Working Party Report. Vox Sang 77:121, 1999. 27. Brown, DL, et al: The in vivo behaviour of complement-coated red cells: Studies in C6-deficient, Ce-depleted and normal rabbits. Clin Exp Immunol 7:401, 1970. 28. Engelfriet, CP, et al: Autoimmune haemolytic anemias: 111 preparation and examination of specific antisera against complement components and products, and their use in serological studies. Clin Exp Immunol 6:721, 1970. 29. Garratty, G, and Petz, LD: The significance of red cell bound complement components in development of standards and quality assurance for the anticomplement components of antiglobulin sera. Transfusion 16:297, 1976. 30. Petz, LD, et al: Clinical Practice of Transfusion Medicine, 3rd ed. Churchill Livingstone, New York, 1996, p 207. 31. Petz, LD, et al: Compatibility testing. Transfusion 21:633, 1981. 32. Howard, JE, et al: Clinical significance of the anticomplement component of antiglobulin antisera. Transfusion 22:269, 1982. 33. Milam JD: Laboratory medicine parameter: Utilizing monospecific antihuman globulin to test blood group compatibility. Am J Clin Pathol 104:122, 1995. 34. Eder, AF: Evaluation of routine pretransfusion direct antiglobulin test in a pediatric setting. Lab Med 24:680, 2003. 35. Judd, WJ, et al: The evaluation of a positive direct antiglobulin test in pretransfusion testing revisited. Transfusion 26:220, 1986. 36. Roback, JD, Combs, MR, Grossman, BJ, and Hillyer, CD (eds): Technical Manual, 16th ed. AABB, Bethesda, MD, 2008. 37. Stroup, M, and MacIlroy, M: Evaluation of the albumin antiglobulin technique in antibody detection. Transfusion 5:184, 1965. 38. Low, B, and Messeter, L: Antiglobulin test in low-ionic strength salt solution for rapid antibody screening and cross-matching. Vox Sang 26:53, 1974. 39. Moore, HC, and Mollison, PL: Use of a low-ionic strength medium in manual tests for antibody detection. Transfusion 16:291, 1976. 40. Shirley, R, et al: Polyethylene glycol versus low-ionic strength solution in pretransfusion testing: A blinded comparison study. Transfusion 34:5, 1994. 41. Barrett, V, et al: Analysis of the routine use of polyethylene glycol (PEG) as an enhancement medium. Immunohematology 11:1, 1995. 42. Jorgensen, J, et al: The influence of ionic strength, albumin and incubation time on the sensitivity of indirect Coombs’ test. Vox Sang 36:186, 1980. 43. Voak, D, et al: Low-ionic strength media for rapid antibody detection: Optimum conditions and quality control. Med Lab Sci 37:107, 1980. 44. Bruce, M, et al: A serious source of error in antiglobulin testing. Transfusion 26:177, 1986. 45. Green, C, et al: Quality assurance of physiological saline used for blood grouping. Med Lab Sci 43:364, 1968. 46. Voak, D, et al: Antihuman globulin reagent specification: The European and ISBT/ICSH view. Biotest Bull 3:7, 1986. 47. Mallory, D, et al: Immunohematology Methods and Procedures. American National Red Cross, Washington, D.C., 1993, pp 40–41.

2682_Ch05_101-118 22/05/12 11:41 AM Page 118

118

PART II

Blood Groups and Serologic Testing

48. Lalezari, P, and Jiang, RF: The manual polybrene test: A simple and rapid procedure for detection of red cell antibodies. Transfusion 20:206, 1980. 49. Crawford, MN, et al: Microplate system for routine use in blood bank laboratories. Transfusion 10:258, 1970. 50. Redman, M, et al: Typing of red cells on microplates by low-ionic polybrene technique. Med Lab Sci 43:393, 1986. 51. Liu, JC, Wang, Y, Liu, FP, and He, YS: The manual polybrene test has limited sensitivities for detecting the Kidd blood group system. Scand J Clin Lab Investig 69:7, 797–800, 2009. 52. Moore, HH: Automated reading of red cell antibody identification tests by a solid phase antiglobulin technique. Transfusion 24:218, 1984. 53. Plapp, FV, et al: A solid phase antibody screen. Am J Clin Pathol 82:719, 1984. 54. Lapierre, Y, et al: The gel test: A new way to detect red cell antigen-antibody reactions. Transfusion 30:2, 1990. 55. Tissot, JD, et al: The direct antiglobulin test: Still a place for the tube technique? Vox Sang 77:223, 1999. 56. Chuansumrit, A, et al: The benefit of the direct antiglobulin test using gel technique in ABO hemolytic disease of the newborn. Southeast Asian J Trop Med Pub Health 28:428, 1997. 57. Lai, M, et al: Clinically significant autoimmune hemolytic anemia with a negative direct antiglobulin test by routine tube test and positive by column agglutination method. Immunohematology 18:109, 2002. 58. Mitek, JF, et al: The value of the gel test and ELAT in autoimmune haemolytic anaemia. Clin Lab Haem 17:311, 1995. 59. Das, SS, Chaudhary, R, and Khetan, D: A comparison of conventional tube test and gel technique in evaluation of direct antiglobulin test. Hematology 12(2):175–178, 2007. 60. Novaretti, MC, Jens, E, Pagliarini, T, Bonifacio, SL, DorlhiacLlacer, PE, and Chamone, DA: Comparison of conventional tube test technique and gel microcolumn assay for direct antiglobulin test: Large study. J Clin Lab Anal 18(5):255–258, 2004.

61. Casina, TS: In search of the Holy Grail: Comparison of antibody screening methods. Immunohematology 22(4):196–202, 2006. 62. Shulman, IA, Maffei, LM, and Downes, KA: North American pretransfusion testing practices, 2001–2004: Results from the College of American Pathologists Interlaboratory Comparison Program survey data, 2001–2004. Arch Pathol Lab Med 129(8):984–989, 2005. 63. Bunker, ML, Thomas, CL, and Geyer, SJ: Optimizing pretransfusion antibody detection and identification: A parallel, blinded comparison of tube PEG, solid-phase, and automated methods. Transfusion 41(5):621–626, 2001. 64. Klostermann, DA, Puca, KE, Scott, EA, and Johnson, ST: Comparison of methods for detection of antenatal anti-D. Transfusion 46(9S):148A, 2006. 65. Weisbach, V, et al: Comparison of the performance of microtube column systems and solid-phase systems and the tube low-ionic-strength solution additive indirect antiglobulin test in the detection of red cell alloantibodies. Transfusion Med 16(4):276–284, 2006. 66. Yamada, C, Serrano-Rahman, L, Vasovic, LV, Mohandas, K, and Uehlinger, J: Antibody identification using both automated solid-phase red cell adherence assay and a tube polyethylene glycol antiglobulin method. Transfusion 48(8):1693–1698, 2008. 67. Dwyre, DM, Erickson, Y, Heintz, M, Elbert, C, and Strauss, RG: Comparative sensitivity of solid phase versus PEG enhancement assays for detection and identification of RBC antibodies. Transfus Apher Sci 35(1):19–23, 2006. 68. Garozzo, G, et al: A comparison of two automated methods for the detection and identification of red blood cell alloantibodies. Blood Transfusion 5(1):33–40, 2007.

2682_Ch06_119-148 28/05/12 12:26 PM Page 119

Chapter

6

The ABO Blood Group System Denise M. Harmening, PhD, MT(ASCP), CLS (NCA); Glenda Forneris, MHS, MT(ASCP)SBB; Barbara J. Tubby MSEd, BS, MT(ASCP)SBB

Introduction Historical Perspective and Routine ABO Testing ABO Antibodies Inheritance of the ABO Blood Groups Formation of A, B, and H Red Cell Antigens Interaction of Hh and ABO Genes Molecular Genetics of ABO Formation of A, B, and H Soluble Antigens

Comparison of A, B, and H Antigens on RBCs with A, B, and H Soluble Substances ABO Subgroups A Subgroups Weak A Subgroups Weak B Subgroups The Bombay Phenotypes (Oh) The Para-Bombay Phenotypes ABH Antigens and Antibodies in Disease

ABO Discrepancies Technical Errors Resolution Categories of ABO Discrepancies Case Study Case 6-1 Summary Chart Review Questions References

OBJECTIVES 1. Describe the reciprocal relationships between ABO antigens and antibodies for blood types O, A, B, and AB. 2. Identify the frequencies of the four major blood types in the white, black, Hispanic, and Asian populations. 3. Explain the effect of age on the production of ABO isoagglutinins. 4. Describe the immunoglobulin classes of ABO antibodies in group O, A, and B individuals. 5. Predict the ABO phenotypes and genotypes of offspring from various ABO matings. 6. Explain the formation of H, A, and B antigens on the red blood cells (RBCs) from precursor substance to immunodominant sugars. 7. Describe the formation of H, A, and B soluble substances. 8. Explain the principle of the hemagglutination inhibition assay for the determination of secretor status. 9. Describe the qualitative and quantitative differences between the A1 and A2 phenotypes. 10. Describe the reactivity of Ulex europaeus with the various ABO groups. 11. Describe the characteristics of the weak subgroups of A (A3, Ax, Aend, Am, Ay, Ael). 12. Describe the characteristics of the Bombay phenotypes. 13. Explain the effects of disease on the expression of ABH antigens and antibodies. 14. Interpret the results from an ABO typing and resolve any discrepancies, if present.

Introduction The ABO system is the most important of all blood groups in transfusion practice. It is the only blood group system in which individuals have antibodies in their serum to antigens that are absent from their RBCs. This occurs without any exposure to RBCs through transfusion or pregnancy. Due to the presence of these antibodies, transfusion of an incompatible

ABO type may result in immediate lysis of donor RBCs. This produces a very severe, if not fatal, transfusion reaction in the patient. Testing to detect ABO incompatibility between a donor and potential transfusion recipient is the foundation on which all other pretransfusion testing is based. Even today, transfusion of the wrong ABO group remains the leading cause of death in hemolytic transfusion reaction fatalities reported to the FDA; however, transfusion-related 119

2682_Ch06_119-148 28/05/12 12:26 PM Page 120

120

PART II

Blood Groups and Serologic Testing

Table 6–1 Transfusion-Related Fatalities by Complication, FY 2009 COMPLICATION

NUMBER

FY09

TRALI

13*

30%

HTR (non-ABO)

8

18%

HTR (ABO)

4

9%

Microbial infection

5

11%

12

27%

Anaphylaxis

1

2%

Other

1**

2%

TACO

TOTALS

44

100%

*In FY 2007, the review committee began using the Canadian Consensus Conference criteria5,6 for evaluating TRALI cases; these numbers include both “TRALI” and “possible TRALI” cases. **Other: Hypotensive Reaction7 Key: HTR = hemolytic transfusion reaction; TACO = transfusionassociated circulatory overload; TRALI = transfusion-related acute lung injury Data from 2009, F. R. (n.d.): Vaccines, Blood & Biologics; U.S. Food and Drug Administration. Fatalities Reported to FDA Following Blood Collection and Transfusion: Annual Summary for Fiscal Year 2009. Retrieved March 22, 2010, from www.fda.gov/BiologicsBloodVaccines/ SafetyAvailability/ReportaProblem/TransfusionDonationFatalities/ucm204763.htm.

acute lung injury (TRALI) was the most frequent cause of death in fiscal year (FY) 20091 (Table 6–1). In FY 2009, there were four reports of fatal hemolytic transfusion reactions due to ABO incompatible blood transfusions (Box 6–1 lists the causes in each of these four cases).1 This chapter presents the ABO blood group system and discusses the biochemistry, properties, and characteristics of ABO antigens and antibodies. In addition, weak subgroups and common discrepancies will be introduced to provide a working knowledge for routine ABO testing.

Historical Perspective and Routine ABO Testing Karl Landsteiner truly opened the doors of blood banking with his discovery of the first human blood group system, ABO. This marked the beginning of the concept of individual uniqueness defined by the RBC antigens present on the RBC

BOX 6–1

Causes of Fatal Hemolytic Transfusion Reactions Due to ABO Incompatible Blood Transfusions in FY 2009 • Case 1: Recipient identification error at the time of transfusion (nursing error) • Case 2: Patient sample labels switched (phlebotomist error) • Case 3: Sample collected from incorrect patient (phlebotomist error) • Case 4: Patient sample mistyped (lab error) Data from 2009, F. R. (n.d.): Vaccines, Blood & Biologics; U.S. Food and Drug Administration. Fatalities Reported to FDA Following Blood Collection and Transfusion: Annual Summary for Fiscal Year 2009. Retrieved March 22, 2010, from www.fda.gov/BiologicsBloodVaccines/SafetyAvailability/ReportaProblem/ TransfusionDonationFatalities/ucm204763.htm.

membrane. In 1901, Landsteiner drew blood from himself and five associates, separated the cells and serum, and then mixed each cell sample with each serum.2 He was inadvertently the first individual to perform forward and reverse grouping. Forward grouping (front type) is defined as using known sources of commercial antisera (anti-A, anti-B) to detect antigens on an individual’s RBCs. Figure 6–1 outlines the steps of performing the forward grouping for ABO (see color insert following page 128), and Table 6–2 lists the results of the forward grouping procedure. Reverse grouping (back type) is defined as detecting ABO antibodies in the patient’s serum by using known reagent RBCs, namely A1 and B cells. Figure 6–2 outlines the steps of performing the reverse ABO grouping (see color insert following page 128), and Table 6–3 summarizes the results of the procedures. Table 6–4 lists the characteristics of the routine reagents used for ABO testing in the blood bank laboratory. ABO forward and reverse grouping tests must be performed on all donors and patients.3 ABO grouping is the

Table 6–2 ABO Forward Grouping: Principle—Detection of Antigens on Patient’s RBCs With Known Commercial Antisera PATIENT RBCS WITH ANTI-A

PATIENT RBCS WITH ANTI-B

INTERPRETATION OF BLOOD GROUP

O

4+

A

4+

B

4+

4+

AB

+ = visual agglutination 0 = negative Note: Reaction gradings vary from patient to patient.

Table 6–3 ABO Reverse Grouping: Principle—Detection of ABO Antibodies (Isoagglutinins) in Serum of Patient With Known Commercial RBCs PATIENT SERUM WITH REAGENT A1 CELLS

PATIENT SERUM WITH REAGENT B CELLS

INTERPRETATION OF BLOOD GROUP

4+

4+

O

3+

A

3+

B

AB

+ = visual agglutination 0 = negative Note: Reaction gradings vary from patient to patient.

2682_Ch06_119-148 28/05/12 12:26 PM Page 121

Chapter 6 The ABO Blood Group System

121

Table 6–4 Characteristics of Routine Reagents Used for ABO Testing Forward Grouping

ANTI-A REAGENT

ANTI-B REAGENT

• Monoclonol antibody*

• Monoclonal antibody*

• Highly specific

• Highly specific

• IgM

• IgM

• Clear blue colored reagent

• Clear yellow colored reagent (contains an acriflavine dye)

• Expected 3+ to 4+ reaction

• Expected 3+ to 4+ reaction

• Usually use 1–2 drops

• Usually use 1–2 drops

REAGENT A1 AND B CELLS • Human source • 4%–5% red cell suspension • Expected 2+ to 4+ reaction usually use one drop

Reverse Grouping

*General rule: Always drop clear solutions first and RBCs second to make sure you have added both a source of antibody and antigen.

most frequently performed test in the blood bank. There is always an inverse reciprocal relationship between the forward and reverse type; thus, one serves as a check on the other. For example, if the individual has A antigens only on their red cells, there will be an “expected” naturally occurring anti-B antibody in their serum since they lack the B antigen. It has been postulated that bacteria, pollen particles, and other substances present in nature are chemically similar to A and B antigens. Bacteria are widespread in the environment, which constantly exposes individuals to A-like and B-like antigens. This exposure serves as a source of stimulation of anti-A and anti-B. All other defined blood group systems do not regularly have in their serum expected “naturally occurring” antibodies to antigens they lack on their RBCs. Antibody production in most other blood group systems requires the introduction of foreign RBCs by transfusion or pregnancy, although some individuals can occasionally have antibodies present that are not related to the introduction of foreign RBCs. (These antibodies are usually of the IgM type and are not consistently present or expected in everyone’s serum.) Therefore, performance of serum

grouping is unique to the ABO blood group system. The regular occurrence of anti-A and/or anti-B in persons lacking the corresponding antigen(s) serves as a confirmation of results in ABO grouping. Table 6–5 summarizes the forward and reverse grouping for the common ABO blood groups. The frequency of these blood groups in the white and black populations is outlined in Table 6–6.4 Group O and A are the most common blood types, and blood group AB is the rarest. However, frequencies of ABO groups differ in a few selected populations and ethnic groups (Table 6–7).4 For example, group B is found twice as frequently in blacks and Asians as in whites. In addition, there is a significant decrease in the distribution of group A in these two ethnic populations in comparison to whites. It has been reported that subgroup A2 is rarely found in Asians.5

ABO Antibodies Individuals normally produce antibodies directed against the A and/or B antigen(s) absent from their RBCs. These antibodies have been described as naturally occurring because they are

Table 6–5 Summary of Forward and Reverse Groupings Forward Group Patient’s Cells With Reagents BLOOD GROUP

ANTI-A

ANTI-B

O

A

4+

B AB

Reverse Group Patient’s Serum With Reagents ANTIGEN(S) ON RBCS

ANTIBODY(IES) IN SERUM

A1 CELLS

B CELLS

No A or B antigen

4+

4+

A and B

A

2+

B

4+

B

3+

A

3+

3+

A and B

No A or B antibodies

0 = negative (no agglutination) + = visual agglutination Note: Reaction gradings vary from patient to patient.

2682_Ch06_119-148 28/05/12 12:26 PM Page 122

122

PART II

Blood Groups and Serologic Testing

Table 6–6 Frequency of ABO Blood Groups in the United States* RACE Blood Group

Whites

Blacks

O

45%

50%

A

40%

26%

B

11%

20%

AB

4%

4%

*Percentages rounded to the nearest whole number Data from Garratty, G, Glynn, SA, and McEntire, R: ABO and Rh (D) phenotype frequencies of different racial/ethnic groups in the United States. Transfusion 44:703–706, 2004.

produced without any exposure to RBCs. The ABO antibodies are predominantly IgM, and they activate complement and react at room temperature or colder.5 ABO antibodies produce strong direct agglutination reactions during ABO testing. The production of ABO antibodies is initiated at birth, but titers are generally too low for detection until the individual is 3 to 6 months of age.6 Therefore, most antibodies found in cord blood serum are of maternal origin. Results of serum ABO testing before 3 to 6 months of age cannot be considered valid because some or all of the antibodies present may be IgG maternal antibodies that have crossed the placenta. As a result, it is logical to perform only forward grouping on cord blood from newborn infants. Antibody production peaks when an individual is between 5 and 10 years of age and declines later in life.6 Elderly people usually have lower levels of anti-A and anti-B; therefore, antibodies may be undetectable in the reverse grouping (see the “ABO Discrepancies” section later in this chapter). ABO antibodies can cause rapid intravascular hemolysis if the wrong ABO group is transfused; this can result in the patient dying.1 Although anti-A (from a group B individual) and anti-B (from a group A individual) contains predominantly IgM antibody, there may be small quantities of IgG present.5 Serum

Table 6–7 ABO Phenotype Frequencies of Ethnic Groups in the United States U.S. FREQUENCIES (%) (ROUNDED TO THE NEAREST WHOLE NUMBER) Phenotype

Whites

Blacks

Hispanic*

Asian**

O

45

50

56

40

A

40

26

31

28

B

11

20

10

25

AB

4

4

3

7

*Hispanic includes Mexican, Puerto Rican, Cuban, and other Hispanics. **Asian includes Chinese, Filipino, Indian, Japanese, Korean, and Vietnamese. Data from Garratty, G, Glynn, SA, and McEntire, R: ABO and Rh (D) phenotype frequencies of different racial/ethnic groups in the United States. Transfusion 44:703–706, 2004.

from group O individuals contains not only anti-A and anti-B but also anti-A,B, which reacts with A and B cells. Anti-A,B antibody activity, originally thought to be just a mixture of anti-A and anti-B, cannot be separated into a pure specificity when adsorbed with either A or B cells.7 For example, if group O serum is adsorbed with A or B cells, the antibody eluted will react with both A and B cells.7 Anti-A,B antibody is not a combination of anti-A and anti-B but is a separate “cross-reacting” antibody that is usually IgG in nature.7 Knowing the amount of IgG anti-A, anti-B, or anti-A,B in a woman’s serum sometimes allows prediction or diagnosis of hemolytic disease of the fetus and newborn (HDFN) caused by ABO incompatibility.8 Often cord blood samples from babies of group O mothers are examined for possible ABO HDFN (see Chapter 19, “Hemolytic Disease of the Fetus and Newborn [HDFN]”). Both immunoglobulin classes of ABO antibodies react preferentially at room temperature (20°C to 24°C) or below and efficiently activate complement at 37°C.9 Testing RBCs with reagent anti-A,B is not required as a routine part of ABO testing.10 However, some believe that anti-A,B is more effective at detecting weakly expressed A and B antigens than reagent anti-A or anti-B. However, the production and use of monoclonal antisera have made antiA and anti-B reagents much more sensitive, to the point where weak A and B antigens can be detected routinely. Therefore, anti-A,B reagent is not usually used in routine ABO red cell testing on patient samples. It is still routinely used when performing ABO confirmation of blood donors, because it is more economical to use one reagent (anti-A,B) than to use two reagents (anti-A and anti-B) to verify group O donor units.3 Reagent anti-A,B can be prepared using blended monoclonal anti-A and anti-B; polyclonal human anti-A,B; or a blend of monoclonal anti-A, anti-B, and antiA,B.3 Consult the manufacturer’s package insert to determine if a reagent anti-A,B reacts with a specific weak A phenotype.

Inheritance of the ABO Blood Groups The theory for the inheritance of the ABO blood groups was first described by Bernstein in 1924. He demonstrated that an individual inherits one ABO gene from each parent and that these two genes determine which ABO antigens are present on the RBC membrane. The inheritance of ABO genes, therefore, follows simple Mendelian genetics. ABO, like most other blood group systems, is codominant in expression.9 (For a review of genetics, see Chapter 2, “Basic Genetics.”) One position, or locus, on each chromosome 9 is occupied by an A, B, or O gene.11,12 The O gene is considered an amorph, as no detectable antigen is produced in response to the inheritance of this gene. Therefore, the group O phenotype is an autosomal recessive trait with the inheritance of two O genes that are nonfunctional. The designations group A and B refer to phenotypes, whereas AA, BO, and OO denote genotypes. In the case of an O individual, both phenotype and genotype are the same, because that individual would have to be homozygous for the O gene. An individual who has the phenotype A (or B) can have the genotype AA or AO (or BB or BO). Box 6–2 lists

2682_Ch06_119-148 28/05/12 12:26 PM Page 123

Chapter 6 The ABO Blood Group System

BOX 6–2

ABO Genotypes and Phenotypes Genotype A1A1 A1A2 A1O A2A2 A2O A1B A2B OO BB BO

Phenotype A1 A1 A1 A2 A2 A1B A2B O B B

the ABO genotypes and phenotypes. Serologically, it is not possible to determine the genotype from the phenotype of an A or B individual. Family studies or molecular assays would have to be performed to determine the exact genotype. The phenotype and genotype are the same in an AB individual because of the inheritance of both the A and B gene. Table 6–8 lists possible ABO phenotypes and genotypes from various matings.

Table 6–8 ABO Groups of Offspring from Various Possible ABO Matings OFFSPRING POSSIBLE PHENOTYPES

MATING GENOTYPES

MATING PHENOTYPES (AND GENOTYPES)

A⫻A

AA ⫻ AA

A (AA)

AA ⫻ AO

A (AA or AO)

AO ⫻ AO

A (AA or AO) or O(OO)

BB ⫻ BB

B (BB)

BB ⫻ BO

B (BB or BO)

BO ⫻ BO

B (BB or BO) or O (OO)

AB ⫻ AB

AB ⫻ AB

AB (AB) or A (AA) or B(BB)

O⫻O

OO ⫻ OO

O (OO)

A⫻B

AA ⫻ BB

AB (AB)

AO ⫻ BB

AB (AB) or B (BO)

AA ⫻ BO

AB (AB) or A (AO)

AO ⫻ BO

AB (AB) or A (AO) or B (BO) or O (OO)

AA ⫻ OO

A (AO)

AO ⫻ OO

A (AO) or O (OO)

AA ⫻ AB

AB (AB) or A (AA)

AO ⫻ AB

AB (AB) or A (AA or AO) or B (BO)

BB ⫻ OO

B (BO)

BO ⫻ OO

B (BO) or O (OO)

BB ⫻ AB

AB (AB) or B (BB)

BO ⫻ AB

AB (AB) or B (BB or BO) or A (AO)

AB ⫻ OO

A (AO) or B (BO)

B⫻B

Formation of A, B, and H Red Cell Antigens The formation of ABH antigens results from the interaction of genes at three separate loci (ABO, Hh, and Se). These genes do not actually code for the production of antigens but rather produce specific glycosyltransferases that add sugars to a basic precursor substance (Table 6–9). A, B, and H antigens are formed from the same basic precursor material (called a paragloboside or glycan) to which sugars are attached in response to specific enzyme transferases elicited by an inherited gene.11–13 The H antigen is actually the precursor structure on which A and B antigens are made. Inheritance of the H gene results in the formation of the H antigen. The H and Se genes are closely linked and located on chromosome 19, in contrast to ABO genes, which are located on chromosome 9. The H and Se genes are not part of the ABO system; however, their inheritance does influence A and B antigen expression. The H gene must be inherited to form the ABO antigens on the RBCs, and the Se gene must be inherited to form the ABO antigens in secretions. The precursor substance on erythrocytes is referred to as type 2. This means that the terminal galactose on the precursor substance is attached to the N-acetylglucosamine in a beta 1 → 4 linkage (Fig. 6–3). A type 1 precursor substance refers to a beta 1 → 3 linkage between galactose and N-acetylglucosamine, which will be described below. ABH antigens on the RBC are constructed on oligosaccharide chains of a type 2 precursor substance.14 The ABH antigens develop early in fetal life but do not increase much in strength during the gestational period. The RBCs of the newborn have been estimated to carry anywhere from 25% to 50% of the number of antigenic sites found on the adult RBC.10 As a result, reactions of newborn RBCs with ABO reagent antisera are frequently weaker than reactions

123

A⫻O

A ⫻ AB

B⫻O

B ⫻ AB

AB ⫻ O

with adult cells. The expression of A and B antigens on the RBCs is fully developed by 2 to 4 years of age and remains constant throughout life.8 In addition to age, the phenotypic expression of ABH antigens may vary with race, genetic interaction, and disease states.15

Interaction of Hh and ABO Genes Individuals who are blood group O inherit at least one H gene (genotype HH or Hh) and two O genes. The H gene elicits the production of an enzyme called α-2-L-fucosyltransferase, which transfers the sugar L-fucose to an oligosaccharide chain on the terminal galactose of type 2 chains.13 The sugars that occupy the terminal positions of this precursor chain and confer blood group specificity are called the immunodominant sugars. Therefore, L-fucose is

2682_Ch06_119-148 28/05/12 12:26 PM Page 124

124

PART II

Blood Groups and Serologic Testing

Table 6–9 Glycosyltransferases and Immunodominant Sugars Responsible for H, A, and B Antigen Specificities GENE

GLYCOSYLTRANSFERASE

IMMUNODOMINANT SUGAR

ANTIGEN

H

α-2-L-fucosyltransferase

L-fucose

H

A

α-3-N-acetylgalactosaminyltransferase

N-acetyl-D-galactosamine

A

B

α-3-D-galactosyltransferase

D-galactose

B

the sugar responsible for H specificity (blood group O; Fig. 6–4). The O gene at the ABO locus, which is sometimes referred to as an amorph, does not elicit the production of a catalytically active polypeptide transferase; therefore, the H substance remains unmodified.13 Consequently, the O blood group has the highest concentration of H antigen. The H substance (L-fucose) must be formed for the other sugars to be attached in response to an inherited A and/or B gene. The H gene is present in more than 99.99% of the random population. Its allele, “h,” is quite rare, and the genotype hh is extremely rare. The term Bombay has been used to refer to the phenotype that lacks normal expression of the ABH antigens because of the inheritance of the hh genotype. The hh genotype does not elicit the production of α-2-L-fucosyltransferase. Therefore, L-fucose is not added to the type 2 chain, and H substance is not expressed on the RBC. Even though Bombay (hh) individuals may inherit ABO genes, normal expression, as reflected in the formation of A, B, or H antigens, does not occur. (See “The Bombay Phenotypes” section.)

In the formation of blood group A, the A gene (AA or AO) codes for the production of α-3-N-acetylgalactosaminyltransferase, which transfers an N-acetyl-D-galactosamine(GalNAc) sugar to the H substance. This sugar is responsible for A specificity (blood group A; Fig. 6–5). The A-specific immunodominant sugar is linked to a type 2 precursor substance that now contains H substance through the action of the H gene. The A gene tends to elicit higher concentrations of transferase than the B gene. This leads to the conversion of practically all of the H antigen on the RBC to A antigen sites. As many as 810,000 to 1,170,000 antigen sites exist on an A1 adult RBC in response to inherited genes.5 Individuals who are blood group B inherit a B gene (BB or BO) that codes for the production of α-3-D-galactosyltransferase, which attaches D-galactose (Gal) sugar to the H substance previously placed on the type 2 precursor substance through the action of the H gene.14 This sugar is responsible for B specificity (blood group B; Fig. 6–6). Anywhere from 610,000 to

(6) CH2OH 0 5 4 D-galactose 3 "1

GAL GLNAC

2

0 (6) CH2OH 5

4 Linkage"

FUC

1

4 Type-2 precursor chain

"H" antigen

Fucose: Immunodominant sugar responsible for "H" specificity

GAL

N-acetylglucosamine 1

GL

Protein

2 NHCOCH3

3

D-galactose

Ceramide

Glucose

Spectrin

( Precursor Structure )

P.S.

HH Hh

L-fucosyl transferase

(genotype inherited) Figure 6–3. Type 2 precursor chain.

Figure 6–4. Formation of the H antigen.

"H" antigen

2682_Ch06_119-148 28/05/12 12:26 PM Page 125

Chapter 6 The ABO Blood Group System

GALNAC GAL

FUC "A" antigen

N-Acetylgalactosamine: Immunodominant sugar responsible for "A" specificity

GLNAC GAL GL

Protein

Ceramide

125

830,000 B antigen sites exist on a B adult RBC in response to the conversion of the H antigen by the α-3-Dgalactosyltransferase produced by the B gene.5 When both A and B genes are inherited, the B enzyme (α-3-D-galactosyltransferase) seems to compete more efficiently for the H substance than the A enzyme (α-3-Nacetylgalactosaminyltransferase). Therefore, the average number of A antigens on an AB adult cell is approximately 600,000 sites, compared with an average of 720,000 B antigen sites.5 Interaction of the Hh and ABO genes is reviewed in Figure 6–7.

Molecular Genetics of ABO Spectrin

AA AO

"H" structure

N-Acetylgalactosaminyl transferase

( genotype inherited ) Figure 6–5. Formation of the A antigen.

D-Galactose: Immunodominant sugar responsible

for "B" specificity

GAL GAL

FUC

"B" antigen

GLNAC GAL

Protein

GL

Ceramide

Spectrin

"H" structure

BB BO

Galactosyl transferase

( genotype inherited ) Figure 6–6. Formation of the B antigen.

"B" antigen

"A" antigen

Advanced Concepts Since the cloning in 1990 of the complementary DNA corresponding to messenger RNA transcribed at the blood group ABO locus,13 more than 200 ABO alleles have been identified by molecular investigation.14,15 The ABO gene is located on chromosome 9 and consists of seven exons.16,17 The last two exons (6 and 7) encode for the catalytic domain of the ABO glycosyltransferases, with most of the coding sequence lying in exon 7. Exons 6 and 7 constitute 77% of the gene.16,17 Amino acid substitutions, resulting primarily from mutations within these two exons of the coding DNA of variant ABO glycosyltransferases, are responsible for transferring the immunodominant sugar to H substance, resulting in ABO phenotypes.18 The seven common ABO alleles include A1, A1variant (A1v), A2, B 1 , O1, O1variant(O1v), and O2.19,20 All ABO antigens arise from mutations in the single ABO gene; however, only three specific mutations, which show a high frequency in the population, indirectly lead to changes in the epitope structures resulting in A, B, or O specificities. Two of the mutations (substitutions) change the specificity of the enzyme from an α-Nacetylgalactosaminyltransferase (the A enzyme) to an α-3-D-galactosyltransferase (the B enzyme).20 These glycosyltransferases, in turn, introduce an α 1,3 N-acetylgalactosamine (A) or an α 1,3 galactose (B) carbohydrate at the ends of type H oligosaccharide (glycan) chains. The third mutation is a deletion within the 5' region of the catalytic domain that results in a frameshift and inactivates the enzyme altogether, leaving the H glycan unmodified.21 These different glycans define the A, B, or O antigens or epitopes. ABO genotyping is complicated by the remarkable diversity at the ABO locus. Recombination or gene conversion between common alleles may lead to hybrids that result in unexpected ABO phenotypes. Furthermore, numerous mutations associated with weak subgroups, nondeletional null (O) alleles, and hybrids resulting from recombinational crossing-over between exons 6 and 7 of chromosome 9, have been described.21 These amino acid substitutions, resulting from deletions, mutations, or gene recombination within these two exons of the coding DNA of variant ABO

2682_Ch06_119-148 28/05/12 12:26 PM Page 126

126

PART II

Blood Groups and Serologic Testing

ar

ug

na

en

"A

g nti

i om

d

a

no

u mm

(i

s nt

)

ine

m sa

to

lac

a lg

ety

ac N-

e

ras

a

l tr

ny

i am

fe ns

s

AO

"H structure"

/ l AA ety ac N-

(immunodominant

BB/BO

Type-2-precursor chain HH / Hh (Precursor structure)

cto

la ga

"B antigen"

(immunodominant

D-galactosyl transferase

L-fucosyl transferase

sugar L-fucose)

sugar galactose)

Aa

nd

hh

B Nge ga ace ne t lac yl s tos ga yl lac t tra os ns am fer in as yl es an d

"A

B

su

ga

an

rs

dg

Precursor structure unchanged

ala

an

tig

en

N-

cto

im

ety

se

(Bombay phenotype)

"(

ac )

mu

lg

no do cto mina nt sa mi ne

ala

Figure 6–7. Interaction of the Hh and ABO genes.

glycosyltransferases, are responsible for the less efficient transfer of the immunodominant sugar to H substance. This results in weak serologic reactions observed in ABO subgroups.17,18

water-soluble secretions produced by tissue cells

Genotype: Se se AB HH

Formation of A, B, and H Soluble Antigens ABH antigens are integral parts of the membranes of RBCs, endothelial cells, platelets, lymphocytes, and epithelial cells.8 ABH-soluble antigens can also be found in all body secretions. Their presence is dependent on the ABO genes inherited and on the inheritance of another set of genes called Sese (secretor genes) that regulate their formation. Eighty percent of the random U.S. population are known as secretors because they have inherited a secretor gene (SeSe or Sese). The inheritance of an Se gene codes for the production of a transferase (α-2-L-fucosyltransferase) that modifies the type 1 precursor substance in secretions to form H substance.22 This H substance can then be modified to express A and B substance (if the corresponding gene is present) in secretions such as saliva. For example, a group A individual who is a secretor (SeSe or Sese) will secrete glycoproteins carrying A and H antigens. However, the Se gene does not affect the formation of A, B, or H antigens on the RBC. It is the presence of the Se gene– specified α-2-L-fucosyltransferase that determines whether ABH-soluble substances will be secreted (Fig. 6–8).22 People who inherit the sese genotype are termed nonsecretors.

H

A

B

= N-Acetylgalactosamine = D-Galactose = N-Acetylglucosamine = L-fucose = Protein backbone

Se H antigen

P.S.

AB

H Figure 6–8. Secretor ABH glycoprotein substances.

A, B, H soluble antigens

2682_Ch06_119-148 28/05/12 12:26 PM Page 127

Chapter 6 The ABO Blood Group System

Comparison of A, B, and H Antigens on RBCs with A, B, and H Soluble Substances The formation of soluble A, B, and H substances is the same as that described for the formation of A, B, and H antigens on the RBCs, except for a few minor distinctions that are compared in Table 6–10. In the past, tests for ABH secretion have been used to establish the true ABO group of an individual whose RBC antigens are poorly developed. The demonstration of A, B, and H substances in saliva is evidence for the inheritance of an A gene, B gene, H gene, and Se gene. The term secretor refers only to secretion of A, B, and H soluble antigens in body fluids. The glycoprotein-soluble substances (or antigens) normally found in the saliva of secretors are listed in Table 6–11. Both ABH red cell antigens and ABH soluble substances are formed due to the attachment of an immunodominant sugar to an oligosaccharide chain. Although several types of oligosaccharide chains exist, types 1 and 3 are primarily associated with body secretions, while types 2 and 4 are associated with the red cell membrane.22 It is interesting to note that types 1 and 2 are more abundant, and they differ only in the linkage position of galactose (Gal) to N-acetylglucosamine (GlcNAc); namely type 1 has a beta 1→3 linkage and type 2 has a beta 1→4 linkage.22 Adding specific immunodominant sugars to the type 2 and 4 chains leads to formation of A, B, and H antigens on the red cell membrane, with the majority being present on type 2 chains.

Table 6–10 Comparison of ABH Antigens on RBCs with A, B, and H Soluble Substances ABH ANTIGENS ON RBCS

A, B, AND H SOLUBLE SUBSTANCES

RBC antigens can be glycolipids, glycoproteins, or glycosphingolipids.

Secreted substances are glycoproteins.

RBC antigens are synthesized only on type 2 precursor chains.

Secreted substances are primarily synthesized on type 1 precursor chains.12

Type 2 chain refers to a beta 1→4 linkage in which the number one carbon of the galactose is attached to the number four carbon of the N-acetylglucosamine sugar of the precursor substance.

Type 1 chain refers to a beta-1→3 linkage in which the number one carbon of the galactose is attached to the number three carbon of the N-acetylglucosamine sugar of the precursor substance.

The enzyme produced by the H gene (α-2-L-fucosyltransferase) acts primarily on type 2 chains, which are prevalent on the RBC membrane.

The enzyme produced by the Se gene (α-2-L-fucosyltransferase) preferentially acts on type 1 chains in secretory tissues.

127

Table 6–11 ABH Substance in the Saliva of Secretors (SeSe or Sese)* SUBSTANCES IN SALIVA ABO Group

A

B

H

O

None

None

↑↑

A

↑↑

None

B

None

↑↑

AB

↑↑

↑↑

* Nonsecretors (sese) have no ABH substances in saliva. ↑↑ and ↑, respectively, represent the concentration of ABH substances in saliva.

Adding the same immunodominant sugars to the type 1 and 3 chains in the body secretions allow for A, B, and H soluble substances to be made in body secretions. Box 6–3 summarizes the body fluids in which ABH-soluble substances can be found. The procedure for determining the secretor status (saliva studies) can be found as Procedure 6-1 on the textbook’s companion website.

ABO Subgroups The original reports of most ABO subgroups were made before the availability of the monoclonal typing reagents currently used in routine ABO grouping. ABO subgroups represent phenotypes that show weaker variable serologic reactivity with the commonly used human polyclonal antiA, anti-B, and anti-A,B reagents.

A Subgroups Basic Concepts In 1911, von Dungern described two different A antigens based on reactions between group A RBCs and anti-A and anti-A1.23 Group A RBCs that react with both anti-A and anti-A1 are classified as A1, whereas those that react with anti-A and not anti-A1 are classified as A2 (Table 6–12 and Figs. 6–9 and 6–10). RBCs from A1 and A2 individuals react BOX 6–3

Fluids in Which A, B, and H Substances can be Detected in Secretors • • • • • • • •

Saliva Tears Urine Digestive juices Bile Milk Amniotic fluid Pathological fluids: pleural, peritoneal, pericardial, ovarian cyst

2682_Ch06_119-148 28/05/12 12:26 PM Page 128

128

PART II

Blood Groups and Serologic Testing

Table 6–12 A1 Versus A2 Phenotypes

gene elicits production of high concentrations of the enzyme α-3-N-acetylgalactosaminyltransferase, which converts almost all of the H precursor structure to A1 antigens on the RBCs. The very potent gene A1 creates from 810,000 to 1,170,000 antigen sites on the adult RBC; whereas inheriting an A2 gene, results in the production of only 240,000 to 290,000 antigen sites on the adult A2 RBC.10 The immunodominant sugar on both A1 and A2 RBCs is N-acetyl-D-galactosamine. Qualitative differences also exist, since 1% to 8% of A2 individuals produce anti-A1 in their serum, and 22% to 35% of A2B individuals produce anti-A1.8 This antibody can cause discrepancies between forward and reverse ABO testing and incompatibilities in crossmatches with A1 or A1B cells. Because anti-A1 is a naturally occurring IgM cold-reacting antibody, it is unlikely to cause a transfusion reaction because it usually reacts only at temperatures well below 37°C. It is considered clinically significant if it is reactive at 37°C. It is now known through ABO genotyping that polymorphism at the ABO locus results in subgroup alleles such as the A2 allele, which is characterized by a single-base substitution at nucleotide 467 and a single-base substitution at nucleotide 1059. These substitutions alter the active site of the coding region and subsequently change the specificity of the A glycosyltransferase.24 It should be noted that in routine forward grouping, the reagent anti-A strongly agglutinates

REACTIONS OF PATIENT’S RBCS WITH Anti-A Reagent (anti-A plus anti-A1)

Anti-A1 Lectin Reagent

A1

+

+

A2

+

Blood Group

+ = positive (agglutination) 0 = negative (no agglutination)

equally strong with current reagent monoclonal anti-A in ABO forward typing tests.2 The A subgroups are generally more common than B subgroups. The weaker serologic reactivity of ABO subgroups is attributed to the decreased number of A and B antigen sites on their red cells. Classification into A1 and A2 phenotypes accounts for 99% of all group A individuals. The cells of approximately 80% of all group A (or AB) individuals are A1 (or A1B), and the remaining 20% are A2 (or A2B) or weaker subgroups. The differences between A1 and A2 are both quantitative and qualitative (Table 6–13). The production of both types of antigens is a result of an inherited gene at the ABO locus. Inheritance of an A1

A1 A A1 A1 A1 A A A 1 A1 A1

A

A

A

Figure 6–9. A1 versus A2 phenotypes.

A

A

A

A

A1

A2

Reactions of Patients’ Red Cells with Blood Group

Antigen Present

A1

A1

A A

A2

A1

A1 A1

A1

A1

A1

Anti-A (Anti-A plus Anti-A1)

Anti-A1 lectin

+

+

+

A

A

A1

A

A

A1

Figure 6–10. A1 versus A2 phenotypes (alternative conceptual presentation).

A

A2

Reactions of Patients’ Red Cells with Blood Group

Antigen Present

Anti-A (Anti-A plus Anti-A1)

Anti-A1 lectin

A1

A1

+

+

A2

A

+

2682_Ch06_119-148 28/05/12 12:26 PM Page 129

Chapter 6 The ABO Blood Group System

Table 6–13 Quantitative and Qualitative Differences of Subgroups A1 and A2 QUANTITATIVE

QUALITATIVE

• ↓ Number of antigen sites

• Differences in the precursor oligosaccharide chains

• ↓ Amount of transferase enzyme

• Subtle differences in transferase enzymes

• ↓ Amount of branching

• Formation of anti-A1, in a percentage of some subgroups

both A1 and A2 phenotypes. Differentiation of A1 and A2 phenotypes can be determined by using a reagent made from the seeds of the plant Dolichos biflorus, which serves as a source of anti-A1. This reagent is known as anti-A1 lectin. Lectins are seed extracts that agglutinate human cells with some degree of specificity. This reagent agglutinates A1 (or A1B) cells but does not agglutinate A2 (or A2B cells). Box 6–4 lists the lectins used in blood banking. The characteristics of the A1 and A2 phenotypes are presented in Table 6–14. Because the A2 glycosyltransferase activity is weaker in adding the immunodominant sugar to the H antigen precursor, A2 red cells will show increased reactivity in comparison to A1 red cells with the reagent anti-H lectin. H antigen is found in greatest concentration on the RBCs of group O individuals. H antigen may not be detectable in group A1 individuals, because in the presence of the A1 gene, almost all of the H antigen is converted to A1 antigen by placing the large N-acetyl-D-galactosamine sugar on the H substance. Because of the presence of so many A1 antigens, the H antigen on A1 and A1B RBCs may be hidden and therefore may not be available to react with anti-H antisera. In the presence of an A2 gene, only some of the H antigen is converted to A antigens, and the remaining H antigen is detectable on the cell.

129

Weak subgroups of the A antigen will often have an inverse reciprocal relationship between the amount of H antigen on the RBC and the amount of A antigens formed (i.e., the more A antigen formed, the less H antigen expressed on the RBC). The H antigen on the RBCs of A1 and A1B individuals is so well hidden by N-acetyl-D-galactosamine that anti-H is occasionally found in the serum. This anti-H is a naturally occurring IgM cold agglutinin that reacts best below room temperature. As can be expected, this antibody is formed in response to a natural substance and reacts most strongly with cells of group O individuals (which have the greatest amount of H substance on their RBCs). Anti-H reacts weakly with the RBCs of A1B individuals (which contain small amounts of H substance). It is an insignificant antibody in terms of transfusion purposes, because it has no reactivity at body temperature (37°C). However, hightitered anti-H may react at room temperature and present a problem in antibody screening procedures, because reagent screening cells are group O (see Chapter 9, “Detection and Identification of Antibodies”). This high-titered anti-H may also present a problem with compatibility testing (see Chapter 10, “Pretransfusion Testing”). Anti-H lectin from the extract of the plant Ulex europaeus closely parallels the reactions of human anti-H. Both antisera agglutinate RBCs of group O and A2 and react very weakly or not at all with groups A1 and A1B.10 Group B cells give reactions of variable strength (Fig. 6–11).

Advanced Concepts The discussion thus far has presented a basic overview of the two major ABO subgroups, A1 and A2. A more plausible, yet more detailed, theory of ABO subgroups has been proposed by the identification of four different forms of H antigens, two of which are unbranched straight chains (H1, H2) and two of which are complex branched chains (H3, H4; Fig. 6–12).22,25 The antigens H1 through H4 correspond to

BOX 6–4

Lectins Used in Blood Banking

O

• Dolichos biflorus—agglutinates A1 or A1B • Bandeiraea simplicifolia—agglutinates B cells • Ulex europaeus—agglutinates O cells (H specificity) and other ABO blood groups depending on the amount of H antigen available.

>

A2

>

B

>

A2B

>

greatest amount of H

A1

>

A1B least amount of H

Figure 6-11. Reactivity of anti-H antisera or anti-H lectin with ABO blood groups.

Table 6–14 Characteristics of A1 and A2 Phenotypes REAGENTS

Phenotypes

ANTIBODIES IN SERUM

OTHER

Common

Unexpected

Substances Present in Saliva of Secretors

Number of Antigen Sites RBC ⫻ 103

Anti-A

Anti-B

Anti-A,B

Anti-A1

A1

4+

4+

4+

Anti-B

None

A, H

810–1,170

A2

4+

4+

Anti-B

Anti-A1 (1%– 8% of cases)

A, H

240–290

2682_Ch06_119-148 28/05/12 12:26 PM Page 130

130

PART II

Blood Groups and Serologic Testing

GALNAC

GALNAC Fuc

Fuc

GAL

GAL GlcNac

GlcNac Aa

H1 GAL

GAL

Glc

GlcNac

H2

Ab

GAL Ceramide Glc

RBC

Ceramide H1 RBC

Fuc

GALNAC

GALNAC

GAL

GAL

GlcNac

H2

Fuc

Fuc

GlcNac

GALNAC GAL

GAL GlcNac GlcNac H3

Ac

Fuc

GALNAC

Fuc

GAL

GAL

GAL GlcNac Glc

GlcNac GAL

GlcNac H4

Ceramide RBC

GAL Glc

H3 Ceramide Denotes immunodominant sugar for H antigen

RBC

Denotes immunodominant sugar for A antigen

H4 Figure 6–12. H-active antigenic structures.

Ad

2682_Ch06_119-148 28/05/12 12:26 PM Page 131

Chapter 6 The ABO Blood Group System

the precursor structures on which the A enzyme can act to convert H antigen to blood group A active glycolipids. Although the chains differ in length and complexity of branching, the terminal sugars giving rise to their antigenic specificity are identical. Studies on the chemical and physical characteristics of the A1 and A2 enzyme transferases have demonstrated that these two enzymes are different qualitatively.13,14 Straight chain H1 and H2 glycolipids can be converted to Aa and Ab antigens, respectively, by both A1 and A2 enzymes, with the A2 enzyme being less efficient. The more complex branched H3 and H4 structures can be converted to Ac and Ad antigens by A1 enzyme and only very poorly by A2 enzyme.25 As a result, more unconverted H antigens (specifically H3 and H4) are available on group A2 RBCs, and only Aa and Ab determinants are formed from H1 and H2 structures.25 On the RBCs of some A2 individuals, Ac is extremely low and Ad is completely lacking (Box 6–5). These are the individuals in whom one would likely find anti-A1 in the serum. This anti-A1 antibody could really be an antibody to Ac and Ad determinants, which these A2 individuals lack. Also, in 22% to 35% of A2B individuals, anti-A1 can be found in the serum. Since the B enzyme transferase is usually more efficient than the A enzyme in converting H structures to the appropriate antigen, A2 enzymes would probably fail completely when paired with a B enzyme. As a result, A2B individuals would be far more likely to lack Ac and Ad components with subsequent production of anti-Ac and anti-Ad (anti-A1).

131

As stated previously, most group A infants appear to be A2 at birth, with subsequent development to A1 a few months later. Newborns have a deficiency of the branched H3 and H4 antigens and therefore the Ac and Ad antigens as well, possibly accounting for the A2 phenotype. Adult cells contain a higher concentration of branched H3 and H4 structures and therefore Ac and Ad determinants of the A antigen in A1 individuals.26

Weak A Subgroups Basic Concepts Subgroups weaker than A2 occur infrequently and are most often recognized through an ABO discrepancy (unexpected reactions in the forward and reverse grouping). These subgroups of A make up 1% of those encountered in the laboratory and therefore are mainly of academic interest.27 Characteristics of weak A subgroups include: • Decreased number of A antigen sites per RBC (resulting in weak or no agglutination with human polyclonal anti-A) • Varying degrees of agglutination by human anti-A,B8 • Increased variability in the detectability of H antigen, resulting in strong reactions with anti-H • Presence or absence of anti-A1 in the serum Secretor studies, adsorption-elution tests, and molecular testing can be utilized to subdivide A individuals into A3, Ax, Aend, etc.28 (Table 6–15). Occasionally, weak subgroups of A may present practical problems; for example, if an Ax donor was mistyped as a group O and was transfused to a group O patient. This is potentially dangerous because the group O patient possesses anti-A,B, which agglutinates and lyses Ax RBCs, causing rapid intravascular hemolysis.

BOX 6–5

Structural Characteristics of A1 and A2 RBCs • A2 RBCs: Predominantly Aa and Ab and unconverted H3 and H4 antigen sites • A1 red cells: Aa, Ab, Ac, and Ad determinants and no unconverted H3 and H4 antigen sites

Table 6–15 Characteristics of Weak ABO Phenotypes REAGENTS

Anti-B

Anti-A,B

OTHER

Anti-A

Anti-B

Anti-A1

Substances present in saliva of secretors

Presence of A transferase in serum

Number of antigen sites RBC ⫻ 103 35

Phenotypes

Anti-A

A3

++mf

++mf

3+

no

Yes

Sometimes

A, H

Sometimes

Ax

wk/0

2+

4+

o/wk

Yes

Almost always

H

Rarely

5

Aend

wk mf

wk mf

4+

no

Yes

Sometimes

H

No

3.5

Am*

0/wk

0/+

4+

no

Yes

No

A, H

Yes

1

Ay*

4+

no

Yes

No

A, H

Trace

1

Ael*

4+

some

Yes

Yes

H

No

.7

*A specificity demonstrated only by absorption/elution procedures 0 = negative; mf = mixed-field agglutination; wk = weak

Anti-H

ANTIBODIES IN SERUM

2682_Ch06_119-148 28/05/12 12:26 PM Page 132

132

PART II

Blood Groups and Serologic Testing

Advanced Concepts Weak A phenotypes can be serologically differentiated using the following techniques: • Forward grouping of A and H antigens with anti-A, anti-A,B, and anti-H • Reverse grouping of ABO isoagglutinins and the presence of anti-A1 • Adsorption-elution tests with anti-A • Saliva studies to detect the presence of A and H substances • Additional special procedures such as molecular testing for mutations or serum glycosyltransferase studies for detecting the A enzyme can be performed for differentiation of weak subgroups.27,28 Absence of a disease process should be confirmed before subgroup investigation, because ABH antigens are altered in various malignancies and other hematologic disorders. (Refer to the “ABH Antigens and Antibodies in Disease” and “ABO Discrepancies” sections). Weak A subgroups can be distinguished as A3, Ax, Aend, Am, Ay, and Ael, using the serologic techniques mentioned previously (see Table 6–15). The characteristics of each weak A subgroup are presented in the following paragraphs. A3 RBCs characteristically demonstrate a mixed-field pattern of agglutination with anti-A and most anti-A,B reagents.6 Mixed-field can be defined as small agglutinates within predominantly unagglutinated red cells. The estimated number of A antigen sites is approximately 35,000 per RBC.6 Weak α-3-N-acetylgalactosaminyltransferase activity is detectable in the serum. However, there appears to be molecular heterogeneity in the A3 glycosyltransferases isolated from various A3 phenotypes. A3 enzyme is a product of an allele at the ABO locus inherited in a dominant manner; however, the A3 blood group has been reported to be very heterogeneous at the molecular level.29–32 Anti-A1 may be present in serum of A3 individuals, and A substance is detected in the saliva of A3 secretors. Ax RBCs characteristically are not agglutinated by anti-A reagent but do agglutinate with most examples of anti-A,B.6 The estimated number of A antigen sites is approximately 4,000 per RBC.33 Anti-A can be adsorbed and then eluted from Ax cells without difficulty. A transferase is not usually detectable in the serum or in the RBC membranes of Ax individuals. The molecular genetics of Ax reflects the considerable heterogeneity of the serologic phenotypes.33 Ax individuals almost always produce anti-A1 in their serum. Routine secretor studies detect the presence of only H substance in Ax secretors. However, Ax secretors contain A substance detectable only by agglutination/inhibition studies using Ax RBCs as indicators.25 Caution should be used in interpreting results of secretor studies using Ax indicator cells and anti-A, because not all Ax cells are agglutinated by anti-A. Aend RBCs characteristically demonstrate mixed-field agglutination with anti-A and anti-A,B, but only a very

small percentage of the RBCs (10% or less) agglutinate.34 The estimated number of A antigen sites on the few agglutinable RBCs is approximately 3,500 per RBC, whereas no detectable A antigens are demonstrated on RBCs that do not agglutinate.34 No A glycosyltransferase is detectable in the serum or in the RBC membranes of Aend individuals. Aend is inherited as an allele at the ABO locus.34 Secretor studies detect the presence of only H substance in the saliva of Aend secretors. Anti-A1 is found in some Aend sera.35 The phenotypes of Afinn and Abantu are considered by some investigators to represent variants of the Aend subgroup.36 Am RBCs are characteristically not agglutinated, or are agglutinated only weakly, by anti-A or anti-A,B.37 A strongly positive adsorption or elution of anti-A confirms the presence of A antigen sites. The estimated number of A antigen sites varies from 200 to 1,900 per RBC in Am individuals.37 An A enzyme of either the A1 or A2 type previously described is detectable in the serum of Am subgroups.37 Am is inherited as a rare allele at the ABO locus.38 These individuals usually do not produce anti-A1 in their sera. Normal quantities of A and H substance are found in the saliva of Am secretors.38 Ay RBCs are not agglutinated by anti-A or anti-A,B. Adsorption and elution of anti-A is the method used to confirm the presence of A antigens. Activity of eluates from Ay RBCs is characteristically weaker than that of eluates from Am RBCs. Trace amounts of A glycosyltransferase is detectable in the serum of Ay individuals, and saliva secretor studies demonstrate H and A substance, with A substance present in below-normal quantities.37 Ay individuals usually do not produce anti-A1. The Ay phenotype can be observed in siblings, implicating a recessive mode of inheritance. This phenotype does not represent expression of an alternate allele at the ABO locus but rather as a germline mutation of an A gene within a family.4 Ael RBCs typically are unagglutinated by anti-A or antiA,B; however, adsorption and elution can be used to demonstrate the presence of the A antigen. No detectable A enzyme activity can be demonstrated in the serum or in the RBC membranes of Ael individuals by glycosyltransferase studies.39 The Ael phenotype is inherited as a rare gene at the ABO locus.39,40 Ael individuals usually produce an anti-A1 that is reactive with A1 cells and sometimes produce anti-A, which agglutinates A2 RBCs.39 Secretor studies demonstrate the presence of only H substance in the saliva of Ael secretors. It should be noted that there are still some reported A variants that do not fit into any of the weak subgroups described, alluding to the existence of new alternate alleles or regulation by modifier genes.41,42 A general flowchart for the process of elimination and identification of various subgroups is presented in Figure 6–13. It is assumed that the patient’s medical history, such as recent transfusion, pregnancy history, disease states, and medications, has been investigated and excluded as a source of the discrepancy.

2682_Ch06_119-148 28/05/12 12:26 PM Page 133

Chapter 6 The ABO Blood Group System

133

Red Cell Reactions with anti-A and/or anti-A,B

weakly agglutinated (possibly A3, Ax, Aend)

no agglutination adsorbs and elutes anti-A (possibly Am, Ay, Ael)

mixed-field (mf) agglutination

⭐10% red cells show very weak mf agglutination

weak agglutination with anti-A,B only 1) anti-A easily adsorbed and eluted 2) secretors demonstrate quantities of A substance in saliva

A3

Aend

Ax

Am

1) anti-A adsorbed and eluted 2) secretors contain small amount of A substance in saliva

Ay

1) anti-A adsorbed and eluted 2) secretors contain only H substance and no A substance in saliva

Ael

Figure 6–13. Investigation of weak A subgroups.

Weak B Subgroups Basic Concepts Subgroups of B are very rare and much less frequent than A subgroups. Subgroups of B are usually recognized by variations in the strength of the reaction using anti-B and anti-A,B. Inheritance of B subgroups, similar to that of the majority of A subgroups, is considered to be a result of alternate alleles at the B locus. Criteria used for differentiation of weak B phenotypes include the following serologic techniques: • Strength and type of agglutination with anti-B, anti-A,B, and anti-H • Presence or absence of ABO isoagglutinins in the serum • Adsorption-elution studies with anti-B • Presence of B substance in saliva • Molecular testing

Advanced Concepts RBCs demonstrating serologic activity that is weaker than normal are designated weak B phenotypes or B subgroups and include B3, Bx, Bm, and Bel phenotypes43 (Table 6–16). There are no B subgroups reported that are equivalent to Aend or Ay. A classification system similar to A subgroups has been used because of common serologic characteristics. Subgroups of B are usually recognized by variations in the strength of the reaction using anti-B and anti-A,B.

Serologic techniques can be used to characterize B subgroups in the following categories: B3, Bx, Bm, and Bel. The B3 phenotype generally results from the inheritance of a rare gene at the ABO locus and is characterized by a mixedfield pattern of agglutination with anti-B and anti-A,B.44 B glycosyltransferase is present in the serum but not in the RBC membranes of these individuals. Anti-B is absent in the serum of B3 phenotypes, but B substance is present in normal amounts in the saliva of secretors. The B3 subgroup is the most frequent weak B phenotype.44,45 Bx RBCs typically demonstrate weak agglutination with anti-B and anti-A,B antisera. B glycosyltransferase has not been detected in the serum or in the RBC membranes of Bx phenotypes, but a weakly reactive anti-B usually is produced.46 Bx RBCs readily adsorb and elute anti-B. Secretor studies demonstrate large amounts of H substance and some B substance that often can only be detected by inhibiting agglutination of Bx cells with anti-B. Family studies suggest that Bx is a rare allele at the ABO locus.47 Bm RBCs are characteristically unagglutinated by anti-B or anti-A,B. The Bm RBCs easily adsorb and elute anti-B. B glycosyltransferase is present in the serum of Bm phenotypes but is usually lower in activity and varies from individual to individual.29 Only very small amounts of B transferase activity is demonstrated in Bm RBC membranes. Reduced activity of B enzyme in hematopoietic tissue is clearly the defect causing the formation of the Bm subgroup, since normal B plasma incubated with Bm RBCs and uracil diphosphate (UDP)-galactose transforms this subgroup into a normal group B phenotype. Anti-B is not

2682_Ch06_119-148 28/05/12 12:26 PM Page 134

134

PART II

Blood Groups and Serologic Testing

Table 6–16 Characteristics of B Phenotypes REAGENTS

Phenotypes

Anti-A

Anti-B

Anti-A,B

Anti-H

ANTIBODIES IN SERUM

OTHER

Common

Unexpected

Substances Present in Saliva of Secretors

Presence of a B Transferase in Serum

B

4+

4+

2+

Anti-A

None

B,H

Yes

B3

++mf

++mf

3+

Anti-A

None

B,H

Yes (wk pos)

Bx

wk

wk

3+

Anti-A

Weak anti-B

H

No

Bm*

0/wk

0/wk

3+

Anti-A

None

B,H

Yes (wk pos)

Bel*

3+

Anti-A

Sometimes a weak anti-B

H

No

*B specificity demonstrated only by adsorption/elution procedures. 0 = negative; mf = mixed-field; wk = weak

characteristically present in the serum of Bm individuals. Normal quantities of H and B substance are found in the saliva of Bm secretors. The Bm phenotype is usually the result of inheritance of a rare allele at the ABO locus, although the subgroup Bm may be the product of an interacting modifying gene linked closely to the ABO locus.48 This modifier gene may depress expression of the B gene, resulting in decreased B enzyme activity.49 The Bm subgroup is reported to be more frequent in Japan.49 Bel RBCs are unagglutinated by anti-B or anti-A,B. This extremely rare phenotype must be determined by adsorption and elution of anti-B. No B glycosyltransferase has been identified in the serum or RBC membrane of Bel individuals. Bel is inherited as a unique mutation in exon 7 of the B gene at the ABO locus.50 A weak anti-B may be present in the serum of this subgroup. Only H substance is demonstrated in saliva of Bel secretors. Other weak B phenotypes have been reported that do not possess the appropriate characteristics for classification into one of the groups previously discussed.51 These may represent new classifications and new representations of ABO polymorphism.

The Bombay Phenotypes (Oh) Basic Concepts The Bombay phenotype was first reported by Bhende in 1952 in Bombay, India.52 It represents the inheritance of a double dose of the h gene, producing the very rare genotype hh. As a result, the ABO genes cannot be expressed, and ABH antigens cannot be formed, since there is no H antigen made in the Bombay phenotype (Box 6–6). More than 130 Bombay phenotypes have been reported in various parts of the world.53 These RBCs are devoid of normal ABH antigens and, therefore, fail to react with anti-A, anti-B, and anti-H. In RBC testing using anti-A and anti-B, the Bombay would phenotype as an O blood group. However, the RBCs of the Bombay phenotype (Oh) do not react with the anti-H lectin (Ulex europaeus), unlike

BOX 6–6

The Bombay Phenotype (Oh) • • • • •

hh genotype No H antigens formed; therefore, no A or B antigens formed Phenotypes as blood group O Anti-A, anti-B, anti-A,B, and anti-H present in the serum Can only be transfused with blood from another Bombay (Oh)

those of the normal group O individual, which react strongly with anti-H lectin.53 Bombay serum contains antiA, anti-B, anti-A,B, and anti-H. Unlike the anti-H found occasionally in the serum of A1 and A1B individuals, the Bombay anti-H can often be potent and reacts strongly at 37°C. It is an IgM antibody that can bind complement and cause RBC lysis. Transfusing normal group O blood (with the highest concentration of H antigen) to a Bombay recipient (anti-H in the serum) would cause immediate cell lysis. Therefore, only blood from another Bombay individual will be compatible and can be transfused to a Bombay recipient. ABH substance is also absent in saliva.53 The (Oh) Bombay phenotype is inherited as an autosomal recessive trait. The underlying molecular defect is most commonly a mutation in the gene FUT1 (H gene), which produces a silenced gene that is incapable of coding for the enzyme, α(1,2)fucosyltransferase (H transferase).53 This enzyme catalyzes the transfer of fucose in an α-1,2 linkage to the terminal galactose of the precursor molecule on RBCs forming the H antigen. This mutation underlying the Bombay phenotype is also associated with a silenced FUT2 gene (Se gene), which normally encodes a very similar α(1,2)fucosyltransferase and normally transfers a fucose to form H antigens in secretions when active.53 Box 6–7 summarizes the general characteristics of the Bombay phenotype. When family studies demonstrate which ABO genes are inherited in the Bombay phenotype, the genes are written as superscripts (OhA, OhB, OhAB).54

2682_Ch06_119-148 28/05/12 12:26 PM Page 135

Chapter 6 The ABO Blood Group System

BOX 6–7

General Characteristics of Bombay Oh (Hnull) Phenotypes • Absence of H, A, and B, antigens; no agglutination with anti-A, anti-B, or anti-H lectin • Presence of anti-A, anti-B, anti-A,B, and a potent wide thermal range of anti-H in the serum • A, B, H nonsecretor (no A, B, or H substances present in saliva) • Absence of α-2-L-fucosyltransferase (H-enzyme) in serum and H antigen on red cells • Presence of A or B enzymes in serum (depending on ABO genotype) • A recessive mode of inheritance (identical phenotypes in children but not in parents) • RBCs of the Bombay phenotype (Oh) will not react with the anti-H lectin (Ulex europaeus) • RBCs of the Bombay phenotype (Oh) are compatible only with the serum from another Bombay individual

The Para-Bombay Phenotypes Advanced Concepts The para-Bombay phenotypes are those rare phenotypes in which the RBCs are completely devoid of H antigens or have small amounts of H antigen present.54 RBCs of these individuals express weak forms of A and B antigens, which are primarily detected by adsorption and elution studies. If a person is genetically A or B, the respective enzymes can be detected, but no H enzyme is detectable, even though it has been shown that there is limited production of H antigen on the RBC.55 The notations Ah and Bh, respectively, have been used to describe these individuals. ABh individuals have also been reported. Ah, Bh, and ABh have been reported mainly in individuals of European origin.54 No H, A, or B antigen is present in the saliva, and anti-H is present in the serum. The serum of Ah individuals contains anti-B and no anti-A, although anti-A1 is usually present.54 In Bh serum, anti-A is always present, and anti-B may be detected.54 It is postulated that homozygous inheritance of a mutant H (FUT1) gene codes for the production of low levels of H transferase activity. The small amount of H substance on the RBC is completely used by the A or B transferase present. This results in small quantities of A or B antigen being present on the RBC with no detectable H antigen. The anti-H present in the serum is weaker in reactivity than the anti-H found in the Bombay phenotype, although it may be reactive at 37°C.55 The genetic basis for the para-Bombays is a mutated FUT1 (H gene) with or without an active FUT2 gene (Se gene) or a silenced FUT1 gene with an active FUT2 gene.56 In the case of the mutated FUT1 gene para-Bombay, the encoded α(1,2)fucosyltransferase enzyme activity is greatly reduced, so very low amounts of H, A, and B antigens are produced. These antigens are serologically undetectable in routine ABO testing. Remember, these very weakly

135

expressed antigens are detectable using only adsorption and elution techniques with the appropriate reagents. In the silenced FUT1 gene with the active FUT2 gene para-Bombays, the α(1,2)fucosyltransferase enzyme associated with the FUT2 gene (α2FucT2) produces H, A, B, type 1 antigens in secretions, including plasma. These type 1 antigens in plasma may adsorb onto the RBC membrane, yielding very weakly expressed H, A, and B antigens, which can be detected only by adsorption and elution techniques. H-deficient secretors have been found in a variety of ethnic groups and nationalities.56 RBCs have little or no A, B, and H antigens. RBCs of Oh secretors are not agglutinated by most examples of anti-H but may be agglutinated by strong anti-H reagents. Adsorption and elution of anti-H may reveal the presence of some H antigen on the RBC.56 Cells are not usually agglutinated by anti-A and anti-B; however, some OhA RBCs can mimic the behavior of Ax cells and can be agglutinated by anti-A,B and potent examples of anti-A. The same reactions with anti-A,B and potent examples of anti-B can be seen with OhB RBCs.4 A weak H-like antibody, called antiIH, that is reactive at low temperature is almost always present in the serum (see Chapter 8, “Blood Group Terminology and the Other Blood Groups”). This antibody is nonreactive with cord cells and is not inhibited by secretor saliva. Because of their secretor status, normal levels of H substances are present in the saliva.55 A and B substances are present in the secretions when A and B genes are present.55

ABH Antigens and Antibodies in Disease Associations between ABH antigens and practically any disorder known to man can be found throughout medical literature. Even more profound are the associations of blood group specificity with such things as a more pronounced “hangover” in A blood groups, “criminality” in group B blood groups, and “good teeth” in group O individuals. There are also several papers correlating blood groups with personality traits. It is no surprise that many scientists refer to these associations as a part of blood group mythology. However, more relevant associations between blood groups and disease are important to the blood banker in terms of blood group serology. Various disease states seem to alter red cell antigens and result in progressively weaker reactions or additional acquired pseudoantigens, which can be seen during forward grouping. Leukemia, chromosome 9 translocations, and any hemolytic disease that induces stress hematopoiesis (e.g., thalassemia)29 have been shown to depress antigen strength. Often the cells will appear to show a mixed-field agglutination (tiny agglutinates in a sea of unagglutinated cells). Hodgkin’s disease also has been reported to weaken or depress ABH red cell antigens, resulting in variable reactions during forward grouping similar to those found in leukemia. The weakening of the antigen tends to follow the course of the disease. The antigen strength will increase again as the patient enters remission.

2682_Ch06_119-148 28/05/12 12:26 PM Page 136

136

PART II

Blood Groups and Serologic Testing

The isoagglutinins (anti-A, anti-B, or anti-A,B) also may be weak or absent in those leukemias demonstrating hypogammaglobulinemia, such as chronic lymphocytic leukemia (CLL). Various lymphomas, such as the malignant (non-Hodgkin’s) variety, may yield weak isoagglutinins, owing to moderate decreases in the gamma globulin fraction. Also, immunodeficiency diseases, such as congenital agammaglobulinemia, will also yield weak or absent isoagglutinins. If this problem is suspected, a simple serum protein electrophoresis will confirm or rule out this condition. Individuals with intestinal obstruction, carcinoma of the colon or rectum, or other disorders of the lower intestinal tract may have increased permeability of the intestinal wall, which allows passage of the bacterial polysaccharides from Escherichia coli serotype O86 into the patient’s circulation. This results in the acquired B phenomenon in group A1 individuals. The patient’s group A red cells absorb the B-like polysaccharide, which reacts with human-source anti-B. A lack of detectable ABO antigens can occur in patients with carcinoma of the stomach or pancreas. The patient’s red cell antigens have not been changed, but the serum contains excessive amounts of blood group–specific soluble substances (BGSS) that may neutralize the antisera utilized in the forward grouping. All these disease states previously mentioned may result in discrepancies between the forward and reverse groupings, indicating that the patient’s red cell group is not what it seems. All ABO discrepancies must be resolved before blood for transfusion is released for that patient. In some cases, secretor or molecular studies may help confirm the patient’s true ABO group.

ABO Discrepancies ABO discrepancies occur when unexpected reactions occur in the forward and reverse grouping. These can be due to problems with the patient’s serum (reverse grouping), problems with the patient’s red cells (forward grouping), or problems with both the serum and cells. The unexpected reaction can be due to an extra positive reaction or a weak or missing reaction in the forward and reverse grouping. All ABO discrepancies must be resolved prior to reporting a patient or donor ABO group.

BOX 6–8

Common Sources of Technical Errors Resulting in ABO Discrepancies • Incorrect or inadequate identification of blood specimens, test tubes, or slides • Cell suspension either too heavy or too light • Clerical errors or incorrect recording of results • A mix-up in samples • Missed observation of hemolysis • Failure to add reagents • Failure to add sample • Failure to follow manufacturer’s instructions • Uncalibrated centrifuge • Overcentrifugation or undercentrifugation • Contaminated reagents • Warming during centrifugation

Resolution If the initial test was performed using RBCs suspended in serum or plasma, repeat testing the same sample using a saline suspension of RBCs can usually resolve the ABO discrepancy. It is important to make sure that any and all technical factors that may have given rise to the ABO discrepancy are reviewed and corrected. It is also essential to acquire information regarding the patient’s age, diagnosis, transfusion history, medications, and history of pregnancy. If the discrepancy persists and appears to be due to an error in specimen collection or identification, a new sample should be drawn from the patient and the RBC and serum testing repeated. When a discrepancy is encountered, results must be recorded, but interpretation of the ABO type must be delayed until the discrepancy is resolved. If blood is from a potential transfusion recipient, it may be necessary to administer group O–compatible RBCs before the discrepancy is resolved. In general, when investigating ABO discrepancies, it should be noted that RBC and serum grouping reactions are very strong (3+ to 4+); therefore, the weaker reactions usually represent the discrepancy. Figure 6–14 shows an algorithm for resolving ABO discrepancies.

Technical Errors Technical errors can also cause ABO discrepancies. This includes errors in labeling the blood sample at the patient’s bedside or in the laboratory; therefore, patient and sample identification are essential! Other errors include the failure to add reagents or the addition of incorrect reagents or sample. Therefore, it is recommended that serum and antiserum be added first, then the patient or reagent red cells. It is also recommended that results be recorded immediately to avoid transcription errors. In addition, contaminated reagents can cause errors in testing. Therefore, looking at all the reagent vials when performing ABO testing and during quality control testing is extremely important. Some of the common causes of technical errors leading to ABO discrepancies in the forward and reverse groupings are listed in Box 6–8.

Categories of ABO Discrepancies ABO discrepancies may be arbitrarily divided into four major categories: group I, group II, group III, and group IV discrepancies. Group I Discrepancies Group I discrepancies are associated with unexpected reactions in the reverse grouping due to weakly reacting or missing antibodies. These discrepancies are more common than those in the other groups listed. When a reaction in the serum grouping is weak or missing, a group I discrepancy should be suspected, because, normally, RBC and serum grouping reactions are very strong (4+). One of the reasons for the missing or weak isoagglutinins is that the patient has depressed anti-

2682_Ch06_119-148 28/05/12 12:26 PM Page 137

Chapter 6 The ABO Blood Group System ABO DISCREPANCY Forward and Reverse testing do not match as expected. Note: The initial testing was performed using patient’s RBCs suspended in serum or plasma.

If an error in specimen collection and identification is suspected. Wash patient’s RBCs with saline and repeat Testing.

No Discrepancy

Same unexpected Rx between Forward and Reverse testing

Report out ABO group

Look up information on Patient: Age, Diagnosis, Medications,Transfusions, and Pregnancy History

Request a new sample to be drawn from the patient.

Repeat Testing

No Discrepancy

Report out ABO group

Determine whether the discrepancy is in the Red Cell or Serum results by observing weakest reactivity.

Example: Patient Serum Problem Weak Reactions in the Reverse grouping

Example: Red Cell Problem Weak Reactions in the Forward grouping

Anti-A 4⫹ Anti-B 4⫹ A1 Cell 2⫹ B Cell 2⫹

Anti-A 2⫹mf Anti-B 0 A1 Cell 0 B Cell 4⫹

Anti-A 1⫹ Anti-B 1⫹ A1 Cell 1⫹ B Cell 2⫹

Probable Group AB with the following possibilities: 1. Cold Reacting Alloantibody (i.e. Anti-M, Anti-P1 most common) 2. Cold Reacting Autoantibody (i.e. Anti-I, Anti-H, Anti-IH) 3. Passively Acquired Antibody (i.e. plasma exchange, mismatched platelets) 4. Rouleaux

Probable Group A with the following possibilities: 1. Out of Group Transfusion (i.e. Group O units transfused to an A patient.) 2. Out of Group Bone Marrow/ Stem Cell Transplantation 3. Leukemia/Lymphoma 4. Fetal-Maternal Bleed 5. A3 Subgroup

Probable Group O with the following possibilities: 1. Cold Autoantibody 2. Cold Autoantibody and Cold Alloantibody 3. Out of Group Bone Marrow/ Stem Cell Transplantation 4. Passively Acquired Antibody

Resolution: (Refer to chapter 9) 1. Run Antibody Screen 2. Run Auto Control 3. Run saline replacement for rouleaux

Resolution: (Refer to chapter 5) 1. Run DAT 2. Run Auto Control

Resolution: 1. Wash patient cells with warm saline and retest 2. Run DAT and Auto Control (Refer to chapter 5) 3. Run Antibody Screen (Refer to chapter 9)

Figure 6–14. Algorithm for resolving ABO discrepancies.

Example: Both Serum and RBC Problem Weak Reaction in both Forward and Reverse grouping

137

2682_Ch06_119-148 28/05/12 12:26 PM Page 138

138

PART II

Blood Groups and Serologic Testing

body production or cannot produce the ABO antibodies. Common populations with discrepancies in this group are: • Newborns (the production of ABO antibodies is not detectable until 4 to 6 months of age) • Elderly patients (the production of ABO antibodies is depressed) • Patients with a leukemia (e.g., chronic lymphocytic leukemia) or lymphoma (e.g., malignant lymphoma) demonstrating hypogammaglobulinemia • Patients using immunosuppressive drugs that yield hypogammaglobulinemia • Patients with congenital or acquired agammaglobulinemia or immunodeficiency diseases • Patients with bone marrow or stem cell transplantations (patients develop hypogammaglobulinemia from therapy and start producing a different RBC population from that of the transplanted bone marrow) • Patients whose existing ABO antibodies may have been diluted by plasma transfusion or exchange transfusion • ABO subgroups Resolution of Common Group I Discrepancies Obtaining the patient’s history may resolve this type of discrepancy, such as a newborn sample that would not have ABO antibodies in the serum until the child was 4 to 6 months of age. If the history indicates an elderly individual, or the diagnosis indicates hypogammaglobulinemia, then the best way to resolve this discrepancy is to enhance the weak or missing reaction in the serum. This is usually performed by incubating the patient serum with reagent A1 and B cells at room temperature for approximately 15 to 30 minutes or by adding one or two drops more plasma or serum to the test. If there is still no reaction after

centrifugation, the serum-cell mixtures can be incubated at 4°C for 15 minutes. An auto control and O cell control must always be tested concurrently with the reverse typing when trying to solve the discrepancy, since the lower temperature of testing will most likely enhance the reactivity of other commonly occurring cold agglutinins (such as anti-I) that react with all adult RBCs (see Chapter 8). Table 6–17 shows a type of discrepancy that may be seen with weak or missing antibodies. The red cell results present a group O individual and the serum results present an AB individual. Since serum problems are more common, it is more likely that the serum immunoglobulins are decreased. Group II Discrepancies Group II discrepancies are associated with unexpected reactions in the forward grouping due to weakly reacting or missing antigens. This group of discrepancies is probably the least frequently encountered. Some of the causes of discrepancies in this group include: • Subgroups of A (or B) may be present (see the “ABO Subgroups” section) • Leukemias may yield weakened A or B antigens (Table 6–18), and Hodgkin’s disease has been reported in some cases to mimic the depression of antigens found in leukemia. • The “acquired B” phenomenon will show weak reactions with anti-B antisera and is most often associated with diseases of the digestive tract (e.g., cancer of the colon). Table 6–19 shows the ABO testing results of an acquired B phenomenon. Resolution of Common Group II Discrepancies The agglutination of weakly reactive antigens with the reagent antisera can be enhanced by incubating the test mix-

Table 6–17 Example of ABO Discrepancy Seen With Weak or Missing Antibodies

Patient

FORWARD GROUPING REACTION OF PATIENT’S CELLS WITH

REVERSE GROUPING REACTION OF PATIENT’S SERUM WITH

Anti-A

Anti-B

A1 Cells

B Cells

Patient’s probable group: O (elderly patient or newborn) Note: The absence of agglutination with reagent cells in the reverse type is because the production of ABO antibodies can be weak or absent in the elderly. Resolution: (1) Check age of the patient. (2) Increase incubation time to 30 minutes (not appropriate for newborn sample). (3) Lower the temperature to 4°C for 15 minutes (include O cells and an autocontrol).

Table 6–18 Serologic Reactions Typical of Leukemia FORWARD GROUPING REACTION OF PATIENT CELLS WITH

REVERSE GROUPING REACTION OF PATIENT SERUM WITH

Anti-A

Anti-B

A1 Cells

B Cells

A

+mf

3+

B

±/+

4+

Patient Phenotype

Note: Weak reactivity with anti-A and anti-B is because the disease, leukemia, has resulted in the weakened expression of the corresponding antigen.

2682_Ch06_119-148 28/05/12 12:26 PM Page 139

Chapter 6 The ABO Blood Group System

139

Table 6–19 Example of ABO Discrepancy Caused by an Acquired B Antigen

Patient

FORWARD GROUPING REACTION OF PATIENT’S CELLS WITH

REVERSE GROUPING REACTION OF PATIENT’S SERUM WITH

Anti-A

Anti-B

A1 Cells

B Cells

4+

2+

4+

Patient’s probable group: A Note: Patient RBCs have acquired a B-like antigen that reacts with reagent anti-B and is associated with cancer of the colon or other diseases of the digestive tract. Resolution: (1) Acidify Anti-B reagent to a pH of 6. (2) Run DAT (refer to Chapter 5, “The Antiglobulin Test”). (3) Run autocontrol.

ture at room temperature for up to 30 minutes, which will increase the association of the antibody with the RBC antigen. If it is still negative, incubate the text mixture at 4°C for 15 to 30 minutes. Include group O and autologous cells as controls. RBCs can also be pretreated with enzymes and retested with reagent antisera. The acquired B antigen arises when bacterial enzymes modify the immunodominant blood group A sugar (N-acetyl-D-galactosamine) into D-galactosamine, which is sufficiently similar to the group B sugar (D-galactose) and cross-reacts with anti-B antisera. This pseudo-B antigen is formed at the expense of the A1 antigen and disappears after recovery.39 The reaction of the appropriate antiserum with these acquired antigens demonstrates a weak reaction, often yielding a mixed-field appearance (see Table 6–19). Blood group reagents of a monoclonal anti-B clone (ES4) strongly agglutinate cells with the acquired B antigen. The pH of reagents containing ES4 has been lowered; consequently, only those cells with the strongest examples of acquired B antigen react with the antisera. Testing the patient’s serum or plasma against autologous RBCs gives a negative reaction, because the anti-B in the serum does not agglutinate the patient’s RBCs with the acquired B antigen. The acquired B antigen is also not agglutinated when reacted with anti-B that has a pH greater than 8.5 or less than 6.40 Secretor studies can be performed when trying to characterize the acquired B phenomenon. If the patient is in fact a secretor, only the A substance is secreted in the acquired B phenomenon. Treating RBCs with acetic anhydride reacetylates the surface molecules, then markedly decreases the reactivity of the cells tested with anti-B. The reactivity of normal B cells is not affected by treatment with acetic anhydride.24

Rare Group II Discrepancies

Advanced Concepts Weakly reactive or missing reactions in RBC grouping may be due to excess amounts of blood group–specific soluble (BGSS) substances present in the plasma, which sometimes occurs with certain diseases, such as carcinoma of the stomach and pancreas. Excess amounts of BGSS substances will neutralize the reagent anti-A or anti-B, leaving no unbound antibody to react with the patient cells. This yields a false-negative or weak reaction in the forward grouping. Washing the patient cells free of the BGSS substances with saline should alleviate the problem, resulting in correlating forward and reverse groupings. Antibodies to low-incidence antigens in reagent anti-A or anti-B may also result in weakly reactive or missing reactions in RBC grouping (Table 6–20). It is impossible for manufacturers to screen reagent antisera against all known RBC antigens. It has been reported (although rarely) that this additional antibody in the reagent antisera has reacted with the corresponding low-incidence antigen present on the patient’s RBCs. This gives an unexpected reaction of the patient’s cells with anti-A or anti-B, or both, mimicking the presence of a weak antigen. The best way to resolve this discrepancy is by repeating the forward type, using antisera with a different lot number. If the cause of the discrepancy is a low-incidence antibody in the reagent antisera reacting with a low-incidence antigen on the patient’s cells, the antibody probably will not be present in a different lot number of reagent. This is only seen when human source antiserum is used. Most ABO reagents in use today are monoclonal antibodies, and these reagents are free of contaminating antibodies to low-incidence antigens. Chimerism is defined as the presence of two cell populations in a single individual (Table 6–21). It was discovered

Table 6–20 Example of ABO Discrepancy Caused by Low-Incidence Antibodies in the Reagent Antisera

Patient

FORWARD GROUPING REACTION OF PATIENT CELLS WITH

REVERSE GROUPING REACTION OF PATIENT SERUM WITH

Anti-A

Anti-B

A1 Cells

B Cells

1+

4+

4+

Patient’s probable group: O Note: Reaction with anti-B in the forward type is due to agglutination between a low-incidence antibody in reagent anti-B and the corresponding antigen on the patient’s cells. Resolution: Use a different lot number for reagent Anti-B

2682_Ch06_119-148 28/05/12 12:26 PM Page 140

140

PART II

Blood Groups and Serologic Testing

Table 6–21 ABO Grouping in Chimera Twins PATIENT

ANTI-A

ANTI-B

ANTI-A,B

A1 CELLS

B CELLS

RBC %

Twin 1

2+mf

2+mf

4+

70% B; 30% O

Twin 2

+wk

+wk

4+

30% B; 70% O

0 = negative; mf = mixed field; wk = weak

in twins (born to a group O mother and group B father) who had a mixture of both B and O cells instead of the expected group of either B or O. Detecting a separate cell population may be easy or difficult, depending on what percentage of cells of the minor population are present. Reactions from chimerism are typically mixed field. True chimerism, which occurs in twins, is rarely found, and the two cell populations will exist throughout the lives of the individuals. In utero exchange of blood occurs because of vascular anastomosis. As a result, two cell populations emerge, both of which are recognized as self, and the individuals do not make anti-A or anti-B. Therefore, expected isoagglutinins are not present in the reverse grouping, depending on the percentage of the population of red cells that exist in each twin. If the patient or donor has no history of a twin, then the chimera may be due to dispermy (two sperm fertilizing one egg) and indicates mosaicism. More commonly, artificial chimeras occur, which yield mixed cell populations as a result of:

• Plasma expanders, such as dextran and polyvinylpyrrolidone • Wharton’s jelly in cord blood samples • Table 6–22 shows an example of ABO discrepancy caused by rouleaux formation. Resolution of Common Group III Discrepancies Rouleaux is a stacking of erythrocytes that adhere in a coinlike fashion, giving the appearance of agglutination. It can be observed on microscopic examination (Fig. 6–15). Cell grouping can usually be accomplished by washing the patient’s RBCs several times with saline. Performing a saline replacement technique will free the cells in the case of rouleaux formation in the reverse type. In this procedure, serum is removed and replaced by an equal volume of saline. In true agglutination, RBC clumping will still remain after the addition of saline. Rouleaux can be a nuisance in the laboratory, since it is an in vitro problem observed during laboratory

• Blood transfusions (e.g., group O cells given to an A or B patient) • Transplanted bone marrows or peripheral blood stem cells of a different ABO type • Exchange transfusions • Fetal-maternal bleeding Group III Discrepancies These discrepancies between forward and reverse groupings are caused by protein or plasma abnormalities and result in rouleaux formation or pseudoagglutination, attributable to: • Elevated levels of globulin from certain disease states, such as multiple myeloma, Waldenström’s macroglobulinemia, other plasma cell dyscrasias, and certain moderately advanced cases of Hodgkin’s lymphomas • Elevated levels of fibrinogen

Figure 6–15. Rouleaux.

Table 6–22 Example of ABO Discrepancy Caused by Rouleaux Formation

Patient

FORWARD GROUPING REACTION OF PATIENT CELLS WITH

REVERSE GROUPING REACTION OF PATIENT SERUM WITH

Anti-A

Anti-B

A1 Cells

B Cells

4+

4+

2+

2+

Patient’s probable group: AB Note: Agglutination with A1 and B cells in reverse type is due to rouleaux formation as a result of increased serum protein or plasma abnormalities. Resolution: (1) Microscopic examination (2) Saline replacement technique (3) Wash cells with saline three times (4) Run antibody screen (refer to Chapter 9)

2682_Ch06_119-148 28/05/12 12:26 PM Page 141

Chapter 6 The ABO Blood Group System

testing. It is not an in vivo problem for the patient. (Refer to companion website for the saline replacement procedure.) Cord blood samples received in the laboratory can also pose a problem in ABO testing, since cord cells may be contaminated with a substance called Wharton’s jelly, which may cause the red cells to aggregate. Washing cord cells six to eight times with saline should alleviate spontaneous rouleaux due to Wharton’s jelly. This substance is a viscous mucopolysaccharide material present on cord blood cells, and thorough washing should result in an accurate ABO grouping. However, because testing is usually not performed on cord serum (because the antibodies detected are usually of maternal origin), reverse grouping may still not correlate with the RBC forward grouping. Group IV Discrepancies These discrepancies between forward and reverse groupings are due to miscellaneous problems and have the following causes: • Cold reactive autoantibodies in which RBCs are so heavily coated with antibody that they spontaneously agglutinate, independent of the specificity of the reagent antibody (Fig. 6–16 and Table 6–23). • Patient has circulating RBCs of more than one ABO group due to RBC transfusion or marrow/stem cell transplant

Figure 6–16. Autoagglutination in a patient with cold agglutinin disease.

141

• Unexpected ABO isoagglutinins • Unexpected non-ABO alloantibodies Resolution of Common Group IV Discrepancies Potent cold autoantibodies can cause spontaneous agglutination of the patient’s cells. These cells often yield a positive direct Coombs’ or antiglobulin test (see Chapter 20, “Autoimmune Hemolytic Anemias”). If the antibody in the serum reacts with all adult cells—for example, anti-I—the reagent A1 and B cells used in the reverse grouping also agglutinate. To resolve this discrepancy, the patient’s RBCs could be incubated at 37°C for a short period, then washed with saline at 37°C three times and retyped. If this is not successful in resolving the forward type, the patient’s RBCs can be treated with 0.01 M dithiothreitol (DTT) to disperse IgM-related agglutination. As for the serum, the reagent RBCs and serum can be warmed to 37°C, then mixed, tested, and read at 37°C. The test can be converted to the antihuman globulin phase if necessary. Weakly reactive anti-A or anti-B may not react at 37°C, which is outside their optimum thermal range. If the reverse typing is still negative (and a positive result was expected), a cold autoabsorption (patient cells with patient serum) could be performed to remove the cold autoantibody from the serum. The absorbed serum can then be used to repeat the serum typing at room temperature. (Refer to Chapter 9 for cold autoadsorption and alloadsorption with rabbit erythrocyte stroma [REST] for the removal of cold autoantibodies.) Unexpected ABO isoagglutinins in the patient’s serum react at room temperature with the corresponding antigen present on the reagent cells (Table 6–24). Examples of this type of ABO discrepancy include A2 and A2B individuals, who can produce naturally occurring anti-A1, or A1 and A1B, individuals who may produce naturally occurring anti-H. (Refer to the previous sections on ABO subgroups.) Serum grouping can be repeated using at least three examples of A1, A2, B cells; O cells; and an autologous control (patient’s serum mixed with patient’s RBCs).3 The specificity of the antibody can be determined by examining the pattern of reactivity (e.g., if the antibody agglutinates only A1 cells, it can most likely be identified as anti-A1). The patient’s RBCs can be tested with Dolichos biflorus to confirm the presence of the ABO subgroup. Dolichos biflorus will agglutinate cells of the A1 but not the A2 phenotype. Unexpected alloantibodies in the patient’s serum other than ABO isoagglutinins (e.g., anti-M) may cause a discrepancy in the reverse grouping (Table 6–25). Reverse grouping

Table 6–23 Example of ABO Discrepancy Caused by Cold Autoantibodies

Patient

FORWARD GROUPING REACTION OF PATIENT CELLS WITH

REVERSE GROUPING REACTION OF PATIENT SERUM WITH

Anti-A

Anti-B

A1 Cells

B Cells

2+

4+

4+

2+

Patient’s probable group: B Note: Reaction with anti-A in forward type is due to spontaneous agglutination of antibody coated cells; reaction with B cells in reverse type is due to cold autoantibody (e.g., anti-I) reacting with I antigen on B cells. Resolution: (1) Wash patient cells with warm saline and retest; (2) Run DAT and autocontrol; (3) Run antibody screen (refer to Chapter 9)

2682_Ch06_119-148 28/05/12 12:26 PM Page 142

142

PART II

Blood Groups and Serologic Testing

Table 6–24 Example of ABO Discrepancy Caused by an Unexpected ABO Isoagglutinin

Patient

FORWARD GROUPING REACTION OF PATIENT CELLS WITH

REVERSE GROUPING REACTION OF PATIENT SERUM WITH

Anti-A

Anti-B

A1 Cells

B Cells

4+

4+

1+

Patient’s probable group: A2B Note: Reactions with patient serum are due to anti-A1 agglutinating A1 reagent red cells. Resolution: (1) Test cells with anti-A1 lectin; (2) Test serum with A1, A2, and O cells; (3) Run an autocontrol

Table 6–25 Example of ABO Discrepancy Caused by an Unexpected Non-ABO Alloantibody

Patient

FORWARD GROUPING REACTION OF PATIENT CELLS WITH

REVERSE GROUPING REACTION OF PATIENT SERUM WITH

Anti-A

Anti-B

A1 Cells

B Cells

4+

4+

1+

1+

Patient’s probable group: AB Note: Reactions with patient serum are due to non-ABO alloantibody agglutinating an antigen other than A1 and B on reagent red cells. Resolution: (1) Run an antibody screen and panel (refer to Chapter 9)

cells possess other antigens in addition to A1 and B, and it is possible that other unexpected antibodies present in the patient’s serum will react with these cells. In this situation, an antibody identification panel should be performed with the patient’s serum. Once the unexpected alloantibodies are identified, reagent A1 and B cells negative for the corresponding antigen can be used in the reverse grouping.

RBCs with the cis-AB phenotype (a rare occurrence) express a weakly reactive A antigen (analogous to A2 cells) and a weak B antigen.4 The B antigen usually yields a weaker reaction with the anti-B from random donors, with mixed-field agglutination typical of subgroup B3

Rare Group IV Discrepancies

Advanced Concepts Antibodies other than anti-A and anti-B may react to form antigen-antibody complexes that may then adsorb onto patient’s RBCs. One example is an individual who has an antibody against acriflavine, the yellow dye used in some commercial anti-B reagents. The acriflavine-antiacriflavine complex attaches to the patient’s RBCs, causing agglutination in the forward type. Washing the patient’s cells three times with saline and then retyping them should resolve this discrepancy. Cis-AB refers to the inheritance of both AB genes from one parent carried on one chromosome and an O gene inherited from the other parent. This results in the offspring inheriting three ABO genes instead of two (Fig. 6–17). The designation cis-AB is used to distinguish this mode of inheritance from the more usual AB phenotype in which the alleles are located on different chromosomes. The cisAB phenotype was first discovered in 1964, when a Polish family was described in which the father was group O, and the mother was group AB and gave birth to children who were all group AB. It was resolved by the fact that the A and B genes were inherited together and were both on the same, or cis, chromosome; thus the term cis-AB.

Group: AB Genotype: AB Chromosomes: A B

Group: O Genotype: OO Chromosomes: O

A B

O

unequal crossing-over (rare occurrence)

Group: AB Genotype: ABO (cis-AB) Chromosomes: A O B

Group: O Genotype: OO Chromosomes: O

O

Group: AB Genotype: ABO (cis-AB) Chromosomes: A O B Figure 6–17. Example of cis-AB inheritance to unequal crossing-over. ο = male; 䊐 = female.

2682_Ch06_119-148 28/05/12 12:26 PM Page 143

Chapter 6 The ABO Blood Group System

reported in several cases. Weak anti-B (present in the serum of most cis-AB individuals) leads to an ABO discrepancy in the reverse grouping. The serum of most cis-AB individuals contains a weak anti-B, which reacts with all ordinary B RBCs, yet not with cis-AB RBCs. A and B transferase levels are lower than those found in ordinary group AB sera.4 Various hypotheses have been offered to explain the cis-AB phenotype. Many favor an unequal crossing over between the A and B gene with gene fusion and the formation of a new gene. However, the banding pattern of the distal end of the long arm of chromosome 9 representing

143

the ABO locus is normal. There have been other examples of cis-ABs that do not fit the above scenario. In these examples, there was a point mutation at the ABO locus, and an enzyme was produced that was capable of transferring both A-specific and B-specific sugars to the precursor molecule.41 Many families have been reported in other parts of the world, with a high incidence of cis-AB being found in Japan. Table 6–26 provides some examples of serologic reactions involving ABO discrepancies, with possible causes and resolution steps. Figure 6–18 provides a simplified summary of ABO discrepancies.

Table 6–26 ABO Discrepancies Between Forward and Reverse Grouping FORWARD GROUPING

REVERSE GROUPING

Anti-A

Anti-B

A1 Cells

B Cells

O Cells

Auto-Control

1

2

4+

1+

4+

3

4+

4+

2+

2+

Patient

Possible Cause

Resolution Steps

Group O newborn or elderly patient; patient may have hypogammaglobulinemia or agammaglobulinemia, or may be taking immunosuppressive drugs

Check age and diagnosis of patient and immunoglobulin levels if possible; incubate at RT for 30 min or at 4°C for 15 min; include group O and autologous cells at 4°C

Subgroup of A: probable A2 with anti-A1

React patient cells with anti-A1 lectin, test serum against additional A1, A2, and O cells; run auto control.

2+

2+

(1) Rouleaux (multiple myeloma patient; any patient with reversed albumin-to-globulin ratio or patients given plasma expanders) (2) Cold autoantibody (probable group AB with an auto anti-I)

(1) Wash RBCs; use saline dilution or saline replacement technique

(3) Cold autoantibody with underlying cold or RT reacting alloantibody (probable group AB with an auto anti-I and a high-frequency cold antibody [e.g., anti-P1, anti-M, anti-Leb])

(2) Perform cold panel and autoabsorb or rabbit erythrocyte stroma (REST) absorb (see Chapter 9) or reverse type at 37°C (3) Perform cold panel autoabsorb or REST, and run panel on absorbed serum; select reverse cells lacking antigen for identified alloantibody; repeat reverse group on absorbed serum to determine true ABO group or at 37°C Continued

2682_Ch06_119-148 28/05/12 12:26 PM Page 144

144

PART II

Blood Groups and Serologic Testing

Table 6–26 ABO Discrepancies Between Forward and Reverse Grouping—cont’d FORWARD GROUPING

REVERSE GROUPING

Anti-A

Anti-B

A1 Cells

B Cells

O Cells

Auto-Control

4

4+

4+

1+

5

4+

4+

6

4+

7

8

4+

9

10

Patient

Possible Cause

Resolution Steps

Subgroup of AB; probabe A2B with anti-A1

Use anti-A1 lectin, test serum against additional A1, A2, and O cells

3+

A1 with potent anti-H

Confirm A1 group with anti-A1 lection; test additional A2, O, and A1 cells and an Oh if available

4+

4+

Oh Bombay

Test with anti-H lection; test Oh cells if available; send to reference laboratory for confirmation

2+

4+

Subgroup of A; probable Ax with anti-A1

Perform saliva studies or absorption/elution

2+

4+

Group A with an acquired B antigen

Check history of patient for lower gastrointestinal problem or septicemia; acidify anti-B typing reagent to pH 6.0 by adding 1 or 2 drops of 1N HCl to 1 mL of anti-B anti-sera, and measure with a pH meter (this acidified anti-B antisera would agglutinate only true B antigens not acquired B antigens), test serum against autologous cells

4+

4+

2+

2+

Group AB with alloantibody

Perform antibody screen and panel, identify room temperature antibody, repeat serum type with antigen negative reagent cells or perform serum type at 37°C

4+

4+

1+

1+

1+

Group B with cold autoantibody

Enzyme-treat RBCs and perform autoabsorption at 4°C or perform prewarmed testing

*AutoAbsorption should not be performed on patient’s cells that have been transfused within the last 3 months. RT = room temperature

2682_Ch06_119-148 28/05/12 12:26 PM Page 145

Chapter 6 The ABO Blood Group System

145

Causes of ABO Discrepancies

Forward (RBCs)

Reverse (plasma)

Missing/weak Antigens

Extra Antigens

Mixed Field

Missing/weak Antibodies

A or B Subgroups

Acquired B (intestinal disease)

Group O transfusions

Disease (leukemia)

Rouleaux (hyperproteinemia)

Stem Cell Transplant

Cold Alloantibodies

Cold Autoantibodies

A3 or B3 Phenotype

Rouleaux (hyperproteinemia)

Newborns, Elderly, Immunocompromised

Passively Acquired Antibody (i.e. plasma exchange, mismatched platelets)

Figure 6–18. Simplified Summary of ABO Discrepancies

1. Where is the discrepancy? 2. What testing would you perform next to resolve the discrepancy?

CASE STUDY Case 6-1 A 45-year-old woman, who has given birth to three children and has a history of five cases of dilation and curettage, is scheduled for a partial hysterectomy at a community hospital. Preoperation laboratory tests include a type and screen. There is no history of transfusions. Part 1 ABO and Rh Typing

Anti-B 0

Anti-A,B 3+

A1Cells 2+

B Cells 4+

Anti-D 3+

Antibody Screen

SCI SCII SCIII

Anti-A1

Cold Autoantibodies

Wharton’s jelly

Anti-A 3+

Extra Antibodies

37°C 0 0 0

AHG 0 0 0

CC √ √ √

Part 2

The patient’s serum was then tested with A2 cells and O cells and the patient’s red cells with Anti-A1 lectin. Patient serum

A2 Cells 0

O Cells 0

Anti-A1 Lectin Patient RBCs 0

3. How would you interpret these results? 4. Why were O+ RBCs chosen for transfusion?

2682_Ch06_119-148 28/05/12 12:26 PM Page 146

146

PART II

Blood Groups and Serologic Testing

SUMMARY CHART

         

ABO frequencies: group O, 45%; group A, 40%; group B, 11%; group AB, 4%. ABO blood group system has naturally occurring antibodies that are primarily IgM. ABO genes, like those of most other blood groups, are inherited in a codominant manner. ABH-soluble antigens are secreted by tissue cells and are found in all body secretions. The antigens secreted depend on the person’s ABO group. ABO reverse grouping is omitted from cord blood testing on newborns, because their antibody titer levels are generally too low for detection. ABO RBC antigens can be glycolipids, glycoproteins, or glycosphingolipids; ABO-secreted substances are glycoproteins. L-fucose is the immunodominant sugar responsible for H specificity. N-acetylgalactosamine is the immunodominant sugar responsible for A specificity. D-galactose is the immunodominant sugar responsible for B specificity. The hh genotype is known as the Bombay phenotype, or Oh, and lacks normal expression of the ABH antigens.

    

 

A specificity is:

1. An ABO type on a patient gives the following reactions:

Patient Cells With

Patient Serum With

Anti-A

Anti-B

A1 cells

B cells

4+

Neg

Neg

What is the patient’s blood type? a. O b. A c. B d. AB 2. The major immunoglobulin class(es) of anti-B in a group

A individual is (are): a. IgM b. IgG c. IgM and IgG d. IgM and IgA 3. What are the possible ABO phenotypes of the offspring

from the mating of a group A to a group B individual? O, A, B A, B A, B, AB O, A, B, AB

a. b. c. d.

Group O persons have the greatest amount of H substance; group A1B persons contain the least amount of H substance. Approximately 80% of the individuals inherit the A gene phenotype as A1; the remaining 20% phenotype as A2 or weaker subgroups. Approximately 1% to 8% of A2 persons produce antiA1 in their serum. Glycoproteins in secretions are formed on type 1 precursor chains. The ABH antigens on RBCs are formed on type 2 precursor chains. Forward and reverse grouping normally yield strong (3+ to 4+) reactions. Group A persons have anti-B in their serum; group B persons have anti-A in their serum; group AB persons have neither anti-A nor anti-B in their serum; group O persons contain both anti-A and anti-B in their serum. Approximately 78% of the random population inherit the Se gene and are termed secretors; the remaining 22% inherit the se gene and are termed nonsecretors. The Se gene codes for the production of L-fucosyltransferase.

4. The immunodominant sugar responsible for blood group

Review Questions

4+

a. L-fucose b. N-acetyl-D-galactosamine c. D-galactose d. Uridine diphosphate-N-acetyl-D-galactose

5. What ABH substance(s) would be found in the saliva of

a group B secretor? H H and A H and B H, A, and B

a. b. c. d.

6. An ABO type on a patient gives the following reactions:

Patient Cells With Anti-A 4+

Patient Serum With

Anti-B

Anti-A1

A1 cells

B cells

4+

Neg

2+

Neg

The reactions above may be seen in a patient who is: a. A1 with acquired B b. A2B with anti-A1 c. AB with increased concentrations of protein in the serum d. AB with an autoantibody

2682_Ch06_119-148 28/05/12 12:26 PM Page 147

Chapter 6 The ABO Blood Group System

7. Which of the following ABO blood groups contains the

least amount of H substance? a. A1B b. A2 c. B d. O 8. You are working on a specimen in the laboratory that

you believe to be a Bombay phenotype. Which of the following reactions would you expect to see? a. Patient’s cells + Ulex europaeus = no agglutination b. Patient’s cells + Ulex europaeus = agglutination c. Patient’s serum + group O donor RBCs = no agglutination d. Patient’s serum + A1 and B cells = no agglutination 9. An example of a technical error that can result in an

ABO discrepancy is: a. Acquired B phenomenon. b. Missing isoagglutinins. c. Cell suspension that is too heavy. d. Acriflavine antibodies. 10. An ABO type on a patient gives the following reactions:

Patient Cells With

Patient Serum With

Anti-A Anti-B A1 cells B cells O cells Autocontrol 4+

Neg

2+

4+

2+

Neg

These results are most likely due to: a. ABO alloantibody. b. Non-ABO alloantibody. c. Rouleaux. d. Cold autoantibody.

References 1. 2009, F. R. (n.d.): Vaccines, Blood & Biologics; U.S. Food and Drug Administration. Fatalities reported to FDA following blood collection and transfusion: Annual summary for fiscal year 2009. Retrieved March 22, 2010, from www.fda.gov/BiologicsBloodVaccines/SafetyAvailability/ReportaProblem/TransfusionDonationFatalities/ucm204763.htm. 2. Landsteiner, K: Uber agglutinationserscheinungen normalen menschlichen blutes. Wien Klin Wschr 14:1132–1134, 1901. 3. Roback, D, Combs, MR, Grossman, BJ, and Hillyer, CD: Technical Manual, 16th ed. American Association of Blood Banks, Bethesda, MD, 2008. 4. Garratty, G, Glynn, SA, and McEntire, R: ABO and Rh (D) phenotype frequencies of different racial/ethnic groups in the United States. Transfusion 44:703–706, 2004. 5. Daniels, G, and Bromilow, I: Essential Guide to Blood Groups. Blackwell Publishing, Malden, MA, 2007. 6. Simon, TL, Snyder, EL, Stowell, CP, Strauss, RG, Solheim, BG, and Petrides, M (eds): Rossi’s Principles of Transfusion Medicine, 4th ed. Wiley-Blackwell, Malden, MA, 2009. 7. Dumont, LJ, AuBuchon, JP, Herschel, L, Roger, J, White, T, and Stassinopoulos, A: Random healthy donor sera show varying effectiveness in hemolyzing ABO Incompatible red blood cells. Blood (ASH Annual Meeting Abstracts) 108(11):958, 2006. 8. Murphy, MF, and Pamphilon, DH: Practical Transfusion Medicine, 3rd ed. Wiley-Blackwell, Hoboken, NJ, 2009.

147

9. Klein, HG, and Anstee, DJ: Mollison’s Blood Transfusion in Clinical Medicine, 11th ed. Blackwell Publishing, Malden, MA, 2005. 10. American Association of Blood Bank Standards, 26th ed. American Association of Blood Banks, Bethesda, MD, 2009. 11. Olsson, ML, and Chester, MA: Polymorphism and recombination events at the ABO locus: A major challenge for genomic ABO blood grouping strategies. Transfus Med 11:295–313, 2001. 12. Chester, MA, and Olsson, ML: The ABO blood group gene: A locus of considerable genetic diversity. Transfus Med Rev 15:177–200, 2001. 13. Yamamoto, F, Clausen, H, White, T, Marken, J, and Hakamori S: Molecular genetic basis of histo-blood group ABO system. Nature 345:229–233, 1990. 14. Cohen, M, Hurtado-Ziola, N, and Varki, A: ABO blood group glycans modulate sialic acid recognition on erythrocytes. Blood 114:3668–3676, 2009. 15. Donghaile, DO, Jenkins, VP, McGrath, R, et al: Defining the molecular mechanisms responsible for the ABO high expresser phenotype. Blood (ASH Annual Meeting Abstracts) 114:2119, 2009. 16. Yamamoto, F: Cloning and regulation of the ABO genes. Transfus Med 11:281–294, 2001. 17. Seltsam, A, et al: Systematic analysis of ABO gene diversity within exons 6 and 7 by PCR screening reveals new ABO alleles. Transfusion 43:428–439, 2003. 18. Olsson, ML, Irshaid, NM, Hosseini-Maaf, B, et al: Genomic analysis of clinical samples with serologic ABO blood grouping discrepancies: Identification of 15 novel A and B subgroup alleles. Blood 98:1585–1593, 2001. 19. Seltsam, A, Hallensleben, M, Kollmann, A, and Blasczyk, R: The nature of diversity and diversification at the ABO locus. Blood 102:3035–3042, 2003. 20. Hosseini-Maaf, B, Hellberg, A, Chester, MA, and Olsson, ML: An extensive polymerase chain reaction-allele-specific polymorphism strategy for clinical ABO blood group genotyping that avoids potential errors caused by null, subgroup, and hybrid alleles. Transfusion 47(11):2110–2125, 2007. 21. Blumenfeld, OO: The ABO gene—more variation! Blood 102:2715, 2003. 22. Svensson, L, Pettersson, A, and Henry, SM: Secretor genotyping for A385T, G428A, C571T, 685delTGG, G849A, and other mutations from a single PCR. Transfusion 40:856–860, 2000. 23. Watkins, WM: The ABO blood group system: Historical background. Transfus Med 11:243–265, 2001. 24. Yan, L, Zhu, F, Liu, Y, Xu, X, and Hong, X: Sequences variations in 5'-flanking region of ABO gene and correlation with ABO alleles in the indigenous Chinese. Vox Sang 94(3):227–233, 2008. 25. Fujitani, N, et al: Expression of H type 1 antigen of ABO histio–blood group in normal colon and aberrant expressions of H type 2 and H type 3/4 antigens in colon cancer. Glycoconj J 17:331–338, 2000. 26. Hosoi, E, Hirose, M, and Hamano, S: Expression levels of H-type alpha (1,2)-fucosyltransferase gene and histo-blood group ABO gene corresponding to hematopoietic cell differentiation. Transfusion 43:65–71, 2003. 27. Mizuno, N, Ohmori, T, Sekiguchi, K, et al: Alleles responsible for ABO phenotype-genotype discrepancy and alleles in individuals with a weak expression of A or B antigens. J Forensic Sci 49(1):21–28, 2004. 28. Seltsam, A, and Blasczyk, R: Missense mutations outside the catalytic domain of the ABO glycosyltransferase can cause weak blood group A and B phenotypes. Transfusion 45(10):1663–1669, 2005. 29. Novaretti, MCZ, Domingues, AE, Pares, MMNS, et al: Rapid detection of 871G>A mutation by sequence specific PCR in ABO*A301 blood donors. Blood (ASH Annual Meeting Abstracts) 104:4098, 2004.

2682_Ch06_119-148 28/05/12 12:26 PM Page 148

148

PART II

Blood Groups and Serologic Testing

30. Barjas-Castro, ML, et al: Molecular heterogeneity of the A3 group. Clin Lab Haematol 22:73–78, 2000. 31. Domingues, AE, Novaretti, MCZ, Dorlhiac-Llacer, PE, and Chamone, DAF: Systematic analysis of ABO gene in A3 and A3B individuals reveals new ABO variants. Blood (ASH Annual Meeting Abstracts) 110:2898, 2007. 32. Olsson, ML, Irshaid, NM, Hosseini-Maaf, B, et al: Genomic analysis of clinical samples with serologic ABO blood grouping discrepancies: Identification of 15 novel A and B subgroup alleles. Blood 98:1585–1593, 2001. 33. Deng, ZH, Yu, Q, Wu, GG, et al: Molecular genetic analysis for Ax phenotype of the ABO blood group system in Chinese. Vox Sang 89(4):251–256, 2005. 34. Nishimukai, H, Fukumori, Y, Tsujimura, R, et al: Rare alleles of the ABO blood group system in two European populations. Leg Med (Tokyo): 11(Suppl 1):S479–S481, 2009. 35. Hillyer, CD (ed): Blood Banking and Transfusion Medicine, 2nd ed. Churchill Livingston Elsevier, Philadelphia, PA, 2007. 36. Hosseini-Maaf, B, Smart, E, Chester, MA, and Olsson ML: The Abantu phenotype in the ABO blood group system is due to a splice-site mutation in a hybrid between a new O1-like allelic lineage and the A2 allele. Vox Sang 88(4):256–264, 2005. 37. Catron, JP, et al: Assay of alpha-N-acetylgalactosaminyltransferase in human sera: Further evidence for several types of Am individuals. Vox Sang 28:347–365, 1975. 38. Asamura, H, et al: Molecular genetic analysis of the Am phenotype of the ABO blood group system. Vox Sang 83:263–267, 2002. 39. Yu, Q, Wu, GG, Liang, YL, Deng, ZH, Su, YQ, and Wang, DM: Study on molecular genetic structure of Ael blood subgroup. Zhonghua Yi Xue Yi Chuan Xue Za Zhi 23(2):173–176, 2006. 40. Sun, CF, Chen, DP, Tseng, CP, Wang, WT, and Liu, JP: Identification of a novel A1v-O1v hybrid allele with G829A mutation in a chimeric individual of AelBel phenotype. Transfusion 46(5):780–789, 2006. 41. Yazer, MH, Hosseini-Maaf, B, and Olsson, ML: Blood grouping discrepancies between ABO genotype and phenotype caused by O alleles. Curr Opin Hematol15(6):618–624, 2008. 42. Zhu, F, Tao, S, Xu, X, et al: Distribution of ABO blood group allele and identification of three novel alleles in the Chinese Han population. Vox Sang 98(4):554–559, 2010. 43. Cai, XH, Jin, S, Liu, X, et al: Molecular genetic analysis for the B subgroup revealing two novel alleles in the ABO gene. Transfusion 48(11):2442–2447, 2008. 44. Cho, D, Yazer, MH, Shin, M, et al: Dispermic chimerism in a blood donor with apparent B3 blood group and mosaic 47,

45.

46.

47.

48. 49. 50. 51.

52. 53.

54. 55. 56.

XYY Syndrome. Blood (ASH Annual Meeting Abstracts). 2005;106(11):1896. Xu, XG, Hong, XZ, Liu, Y, Zhu, FM, Lv, HJ, and Yan, LX: A novel M142T mutation in the B glycosyltransferase gene associated with B3 variant in Chinese. Zhonghua Yi Xue Yi Chuan Xue Za Zhi 26(3):254–257, 2009. Hosseini-Maaf, B, Letts, JA, Persson, M, et al: Structural basis for red cell phenotypic changes in newly identified, naturally occurring subgroup mutants of the human blood group B glycosyltransferase. Transfusion 47(5):864–875, 2007. Seltsam, A, Wagner, FF, Gruger, D, Gupta, CD, Bade-Doeding, C, and Blasczyk, R: Weak blood group B phenotypes may be caused by variations in the CCAAT-binding factor/NF-Y enhancer region of the ABO gene. Transfusion 47(12):2330– 2335, 2007. Seltsam, A, Gruger, D, Just, B, et al: Aberrant intracellular trafficking of a variant B glycosyltransferase. Transfusion 48(9):1898–1905, 2008. Koscielak, J, Pacuszka, T, and Dzierkowa-Borodej, W: Activity of B-gene-specified galactosyltransferase in individuals with Bm phenotypes. Vox Sang 30:58–67, 1976. Lin, PH, et al: A unique 502C>T mutation in exon 7 of ABO gene associated with the Bel phenotype in Taiwan. Transfusion 43:1254–1259, 2003. Hosseini-Maaf, B, Hellberg, A, Rodrigues, MJ, Chester, MA, and Olsson, ML: ABO exon and intron analysis in individuals with the A weak B phenotype reveals a novel O1v-A2 hybrid allele that causes four missense mutations in the A transferase. BMC Genet 4:17, 2003. Bhende, YM, Deshpande, CK, Bhatia, HM, et al: A “new” blood group characteristic related to the AB0 system. Lancet 1:9034, 1952. Storry, et al: Identification of six new alleles at the FUT1 and FUT2 loci in ethnically diverse individuals with Bombay and para-Bombay phenotypes. Transfusion 46(12):2149–2155, 2006. Salmon, C, et al: H-deficient phenotypes: A proposed practical classification of Bombay Ah, H2, Hm. Blood Transfus Immunohaematol 23:233–248, 1980. Yan, L, Zhu, F, Xu, X, Hong, X, and Lv, Q: Molecular basis for para-Bombay phenotypes in Chinese persons, including a novel nonfunctional FUT1allele. Transfusion 45:725–730, 2005. Storry, JR, and Olsson, ML: The ABO blood group system revisited: a review and update. Immunohematology, vol 25(2):48–59, 2009.

2682_Ch07_149-171 22/05/12 11:43 AM Page 149

Chapter

7

The Rh Blood Group System Susan T. Johnson, MSTM, MT(ASCP)SBB and Merilyn Wiler, MA, MT(ASCP)SBB

Introduction History Terminology Fisher-Race: DCE Terminology Wiener: Rh-Hr Terminology Rosenfield and Coworkers: Alphanumeric Terminology International Society of Blood Transfusion Committee: Updated Numeric Terminology Overview of Rh Terminologies Molecular Genetics Rh Genes Rh-Positive Phenotypes Rh-Negative Phenotypes Biochemistry Rh Function Weak D: Variations of D Antigen Expression C in Trans to RHD Weak D

Partial D Del D Epitopes on RhCE Protein Detection of Rh Antibodies and Antigens Rh Antibodies Rh Typing Reagents Clinical Considerations Transfusion Reactions Hemolytic Disease of the Fetus and Newborn Rh Deficiency Syndrome: Rhnull and Rhmod Unusual Phenotypes and Rare Alleles Cw f (ce) rhi (Ce) G Rh13, Rh14, Rh15, and Rh16 Rh17 (Hr0) Rh23, Rh30, and Rh40

Rh33 (Har) Rh32 Rh43 (Crawford) e Variants V and VS Deletions Landsteiner Weiner Blood Group System Case Studies Case 7-1 Case 7-2 Case 7-3 Summary Chart Review Questions References

OBJECTIVES Explain the derivation of the term Rh. 1. Differentiate Rh from LW blood group systems. 2. Compare and contrast the Fisher-Race and Wiener theories of Rh inheritance. 3. Translate the five major Rh antigens, haplotypes, and predicted haplotypes, from one nomenclature to another, including Fisher-Race, Wiener, Rosenfield, and ISBT. 4. Define the basic biochemical structure of Rh. 5. Compare and contrast the genetic pathways for the regulator type of Rhnull and the amorphic Rhnull. 6. Describe and differentiate five mechanisms that result in weakened expression of D on red blood cells. 7. List one instance in which the weak-D status of an individual must be determined. 8. List and differentiate four types of Rh typing reagents, and provide two advantages of each type. 9. Define three characteristics of Rh antibodies. 10. Describe three symptoms associated with an Rh hemolytic transfusion reaction. 11. Compare and contrast Rhnull and Rhmod and describe the role of RhAG in Rh antigen expression. 12. List four Rh antigens (excluding DCcEe), and give two classic characteristics of each antigen. 13. Determine the most probable genotype of an individual when given the individual’s red blood cell typing results, haplotype frequencies, and ethnicity. 149

2682_Ch07_149-171 22/05/12 11:43 AM Page 150

150

PART II

Blood Groups and Serologic Testing

Introduction This chapter describes in detail the Rh blood group system. It is imperative to have a basic understanding of Rh, as RhD typing is a critical component of pretransfusion testing. In addition, clinically important Rh antibodies are relatively common in pregnancy and in patients requiring blood transfusion. The term Rh refers to a specific red blood cell (RBC) antigen (D) and to a complex blood group system currently composed of over 50 different antigenic specificities. Although Rh antibodies were among the first to be described, scientists have spent years unraveling the complexities of the Rh blood group system from its serology to its mode of inheritance, genetic control, and the biochemical structure of the Rh antigens. Rh-specific antigens reside on proteins versus the carbohydrate antigens ABO and Hh. Rh is the second most important blood group system in terms of transfusion, as the Rh system antigens are very immunogenic. Unlike ABO antibodies that are typically found in individuals who lack the corresponding antigen, Rh antibodies are produced only after exposure to foreign red blood cells. Once present, they can produce significant hemolytic disease of the fetus and newborn (HDFN) as well as hemolytic transfusion reactions. The terms Rh-positive or positive and Rh-negative or negative are routinely used by the public and by experts in the field when referring to blood type—for example, A-positive or A-negative. Rh-positive indicates that an individual’s red blood cells possess one particular Rh antigen, the D antigen, on their red blood cells. Rh-negative indicates that the red blood cells lack the D antigen.

History Before 1939, the only significant blood group antigens recognized were those of the ABO system. Transfusion medicine was thus based on matching ABO groups. Despite ABO matching, blood transfusions continued to result in morbidity and mortality. As the 1930s ended, two significant discoveries were made that would further the safety of blood transfusion and eventually define the most extensive blood group system known. It began when Levine and Stetson1 described a hemolytic transfusion reaction in an obstetrical patient. After delivering a stillborn infant, this woman required transfusions. Her husband, who had the same ABO type, was selected as her donor. After transfusion, the recipient demonstrated classic symptoms of an acute hemolytic transfusion reaction (AHTR). Subsequently, an antibody was isolated from the mother’s serum that reacted both at 37°C and at 20°C with the father’s RBCs. It was postulated that the fetus and the father possessed a common factor the mother lacked. While the mother carried the fetus, she was exposed to this factor and subsequently produced an antibody that showed positive reactivity when tested against the transfused RBCs from the father. One year later, Landsteiner and Wiener2 reported on an antibody made by guinea pigs and rabbits when they were transfused with Rhesus macaque monkey RBCs. This antibody,

which agglutinated 85% of human RBCs, was named Rh after the Rhesus monkey. Another investigation by Levine and coworkers3 demonstrated that the agglutinin (antibody causing direct agglutination of RBCs) causing the hemolytic transfusion reaction and the antibody described by Landsteiner and Wiener appeared to define the same blood group. Many years later it was recognized that the two antibodies were different. However, the name Rh was retained for the human-produced antibody, and anti-Rhesus formed by the animals was renamed anti-LW in honor of those first reporting it (Landsteiner and Wiener). Further research resulted in defining Rh as a primary cause of hemolytic disease of the fetus and newborn (HDFN, also called erythroblastosis fetalis) and a significant cause of hemolytic transfusion reactions. Continued investigation4–7 showed additional blood group factors were associated with the original agglutinin. By the mid-1940s, five antigens made up the Rh system. Today the Rh blood group system contains over 57 different specificities and continues to grow in number as new genetic mutations are discovered.

Terminology Terminologies used to describe the Rh system are derived from four sets of investigators. Two terminologies are based on postulated genetic theories of Rh inheritance. The third common terminology used describes only the presence or absence of a given antigen. The fourth is the result of the combined efforts of the International Society of Blood Transfusion (ISBT) Committee on Terminology for Red Cell Surface Antigens. The molecular basis of the Rh blood group system as we know it today is described in detail in the “Molecular Genetics” section after the discussion of nomenclature to provide context to the terminology used.

Fisher-Race: DCE Terminology In the 1940s, Fisher and Race8 were investigating antigens found on human RBCs, including the newly defined Rh antigen. They postulated that the antigens of the system were produced by three closely linked sets of alleles (Fig. 7–1). Each gene was responsible for producing a product (or antigen) on the RBC surface. Each antigen and corresponding gene were given the same letter designation (when referring to the gene, the letter is italicized). Fisher and Race named the antigens of the system D, d, C, c, and E, e. Now it is known that “d” represents the

Antigens D

D Gene Close Linkage

Production C / c Gene

C/c Pathway

E / e Gene

E/e RBC Surface

Figure 7–1. Fisher-Race concept of Rh (simplified). Each gene produces one product.

2682_Ch07_149-171 22/05/12 11:43 AM Page 151

Chapter 7 The Rh Blood Group System

Table 7–1 Frequency of Common Rh Antigens in Caucasians ANTIGEN

GENE FREQUENCY (%)

D

85

No D (absence of D)

15

C

70

E

30

c

80

e

98

absence of D antigen; however, the term continues to be utilized with Fisher-Race terminology as a placeholder. The phenotype (antigens expressed on the RBC detected by typing) of a given RBC is defined by the presence of D, C, c, E, and e expression. The gene frequency in the Caucasian population for each Rh antigen is given in Table 7–1, and the Rh haplotype (the complement of genes inherited from either parent) frequencies are given in Table 7–2. Notice how the frequencies vary with ethnic background. According to the Fisher-Race theory, each person inherits a set of Rh genes from each parent (i.e., one D or d, one C or c, and one E or e) (see Fig. 7–1). Because Rh genes were thought to be codominant, each inherited gene expresses its corresponding antigen on the RBC. The combination of maternal and paternal haplotypes determines one’s genotype (the Rh genes inherited from each parent) and dictates one’s phenotype. An individual’s Rh phenotype is reported as DCE rather than CDE because Fisher postulated that the C/c locus lies between the D/d and E/e loci. This information is based on frequencies of the various gene combinations.

Table 7–2 Fisher-Race Haplotypes of the Rh System PREVALENCE (%) Haplotype

White

Black

Asian

DCe

42

17

70

dce

37

26

3

DcE

14

11

21

Dce

4

44

3

dCe

2

2

2

dcE

1

< 0.01

< 0.01

DCE

< 0.01

< 0.01

1

dCE

< 0.01

< 0.01

< 0.01

Modified from Roback, JD, Combs, MR, Grossman, B, Hillyer, C (eds): Technical Manual, 16th ed. AABB, Bethesda, MD, 2008.

151

It is essential to remember that d does not represent an antigen but simply represents the absence of D antigen. C, c, E, and e represent actual antigens recognized by specific antibodies. There has never been an antibody that recognizes d antigen, supporting the fact that d antigen does not exist. Further discussion on the absence of D follows later in the chapter. For many students and working laboratory scientists, the Fisher-Race terminology represents the easiest way to think about the five major Rh system antigens, but it has shortcomings. Many antigens assigned to the Rh blood group system were given names using a variety of terminologies. In addition, as the number of Rh antigens continues to grow, the original Fisher-Race terminology is becoming too limiting. In very rare instances, an individual may fail to express any allelic antigen at one or both Rh loci; that is, a person may lack E and e, or all CcEe antigens. The probable genotype for the Rh (D)-positive person exhibiting a deletion phenotype such as these is written DC- or Dc-, or D–. A deletion of Cc with Ee has not been reported. The person expressing no Rh antigens on the RBC is said to be Rhnull, and the phenotype may be written as —/—. Weakened expression of all Rh antigens of an individual has also been reported. These individuals are said to have the Rhmod phenotype. Placing parenthesis around (D), (C), and (e) indicates weakened antigen expression.

Wiener: Rh-Hr Terminology In his early work defining the Rh antigens, Wiener9 believed there was one gene responsible for defining Rh that produced an agglutinogen containing a series of blood factors. According to Weiner, this Rh gene produced at least three factors within an agglutinogen (Fig. 7–2). The agglutinogen may be considered the phenotypic expression of the haplotype. Each factor is an antigen recognized by an antibody. Antibodies can recognize single or multiple factors (antigens). Table 7–3 lists the major agglutinogens and their respective factors, along with the shorthand term that has come to represent each agglutinogen. Wiener’s terminology is complex and unwieldy; nevertheless, many blood bankers use modified Wiener terminology interchangeably with other nomenclatures. This terminology allows one to convey Rh antigens inherited on one chromosome or haplotype and makes it easier to discuss a genotype. A medical laboratory scientist conveying a probable genotype to a coworker would have to say DcE/DcE. However, R2R2 is much easier to verbally communicate.

Agglutinogen

Rh° gene

Rh Factor

Factor Rh0

Rh0

Factor hr'

hr'

Factor hr''

hr'' RBC Surface

Figure 7–2. Wiener’s agglutinogen theory. Antibody will recognize each factor within the agglutinogen.

2682_Ch07_149-171 22/05/12 11:43 AM Page 152

152

PART II

Blood Groups and Serologic Testing

Table 7–3 Rh-Hr Terminology of Wiener GENE

AGGLUTINOGEN

BLOOD FACTORS

SHORTHAND DESIGNATION

FISHER-RACE ANTIGENS

Rh0

Rh0

Rh0hr’hr’’

R0

Dce

Rh1

Rh1

Rh0rh’hr’’

R1

DCe

Rh2

Rh2

Rh0hr’rh’’

R2

DcE

Rhz

Rhz

Rh0rh’rh’’

Rz

DCE

rh

rh

hr’hr’’

r

ce

rh‘

rh’

rh’hr’’

r’

Ce

rh‘’

rh’’

hr’rh’’

r’’

cE

rhy

rhy

rh’rh’’

ry

CE

Standard type is used to describe the gene product or agglutinogen. Subscripts are used with the uppercase R and superscripts with the lowercase r (i.e., R1 or R2 or r⬘). Phenotypes of Rhnull and Rhmod are written as stated. The genotype for the Rhnull that arises from an amorphic gene at both Rh loci is written as 苷 rr and pronounced “little r double bar.” When referring to the Rh antigens (or blood factors) in Wiener nomenclature, the single prime (⬘) refers to either C or c and the double prime (⬙) to either E or e. If the r precedes the h (i.e., rh⬘ or rh⬙), this refers to the C or E antigens, respectively. When the h precedes the r, this refers to either the c (hr⬘) or e (hr⬙) antigen. Rh0 is equivalent to D. In the Wiener nomenclature, there is no designation for the absence of D antigen. By using these designations, the laboratorian should be able to recognize immediately which antigens are present on the RBCs described. However, it is difficult to use the Wiener nomenclature to adequately describe additional alleles within an agglutinogen. Because of this, many of the more recently described antigens of the Rh system have not been given Rh-Hr designations.

Fisher-Race nomenclature may be converted to Wiener nomenclature and vice versa. It is important to remember that an agglutinogen in Wiener nomenclature actually represents the presence of a single haplotype expressing three different antigens (see Table 7–3). When describing an agglutinogen, the uppercase R denotes the presence of the original factor, the D antigen. The lowercase r indicates the absence of D antigen. The presence of uppercase C is indicated by a 1 or a single prime (⬘). Lowercase c is implied when there is no 1 or ⬘ indicated. (It is assumed that the third antigen is e). That is, R1 is the same as DCe; r⬘ denotes Ce; and R0 is equivalent to Dce. The presence of E is indicated by the Arabic number 2 or double prime (⬙). Lowercase e is implied when there is no 2 or ⬙ indicated—that is, R2 is the same as DcE; r⬙ denotes cE, and r is equivalent to ce. (Again, it is assumed that a c antigen is present.) When both C and E are uppercase, the letter z or y is used. Rz denotes DCE, whereas ry represents CE. See Table 7–4 for a summary of this shorthand nomenclature. Italics or superscripts are used when describing Rh genes in the Wiener nomenclature (i.e., R1 or R2, R1 or R2).

Table 7–4 Weiner Haplotype Terminology SYMBOL

D

C

E

c*

e*

SHORTHAND DESIGNATION

R

1

+

+

+

R1

r

+

+

r’

R

2

+

+

+

R2

r

‘’

+

+

r’’

R

Z

+

+

+

Rz

r

y

+

+

ry

R

+

+

+

R0

r

None

+

+

r

*c and e typings are assumed based on symbols used to indicate phenotype.

2682_Ch07_149-171 22/05/12 11:43 AM Page 153

Chapter 7 The Rh Blood Group System

153

Rosenfield and Coworkers: Alphanumeric Terminology

International Society of Blood Transfusion Committee: Updated Numeric Terminology

As the Rh blood group system expanded, it became more difficult to assign names to new antigens using existing terminologies. In the early 1960s, Rosenfield and associates10 proposed a system that assigns a number to each antigen of the Rh system in order of its discovery or recognized relationship to the Rh system (Table 7–5). This system has no genetic basis, nor was it proposed based on a theory of Rh inheritance, but it simply demonstrates the presence or absence of the antigen on the RBC. A minus sign preceding a number designates the absence of the antigen. If an antigen has not been typed, its number will not appear in the sequence. An advantage of this nomenclature is that the RBC phenotype is thus succinctly described. For the five major antigens, D is assigned Rh1, C is Rh2, E is Rh3, c is Rh4, and e is Rh5. For RBCs that type D + C + E + c negative, e negative, the Rosenfield designation is Rh: 1, 2, 3, –4, –5. If the sample was not tested for e, the designation would be Rh: 1, 2, 3, –4. All Rh system antigens have been assigned a number. The numeric system is well suited to electronic data processing. Its use expedites data entry and retrieval. Its primary limiting factor is that there is a similar nomenclature for numerous other blood groups such as Kell, Duffy, Kidd, Lutheran, Scianna, and more. K:1,2 refers to the K and k antigens of the Kell blood group system. Therefore, when using the Rosenfield nomenclature on the computer, one must use both the alpha (Rh:, K:) and the numeric (1, 2, –3, etc.) to denote a phenotype.

As the world of blood transfusion began to cooperate and share data, it became apparent there was a need for a universal language. The International Society of Blood Transfusion (ISBT) formed the Committee on Terminology for Red Cell Surface Antigens. Its mandate was to establish a uniform nomenclature that is both eye- and machine-readable and is in keeping with the genetic basis of blood groups.11 The ISBT adopted a six-digit number for each authenticated antigen belonging to a blood group system. The first three numbers represent the system and the remaining three the antigenic specificity. Number 004 was assigned to the Rh blood group system, and then each antigen assigned to the Rh system was given a unique number to complete the six-digit computer number. Table 7–6 provides a listing of these numbers. When referring to individual antigens, an alphanumeric designation similar to the Rosenfield nomenclature may be used. The alphabetic names formerly used were left unchanged but were converted to all uppercase letters (e.g., Rh, Kell became RH, KELL). Therefore, D is RH1, C is RH2, and so forth. (Note: There is no space between the RH and the assigned number.) The phenotype designation includes the alphabetical symbol that denotes the blood group, followed by a colon and then the specificity numbers of the antigens defined. A minus sign preceding the number indicates that the antigen was tested for but was not present. The phenotype D + C – E + c + e + or DcE/ce or R2r would be written RH:1, –2, 3, 4, 5.

Table 7–5 Common Rh Types by Three Nomenclatures

Common genotypes

Rarer genotypes

PHENOTYPE FREQUENCY (%) (APPROX., CAUCASIAN)

WIENER

FISHER-RACE

ROSENFIELD PHENOTYPE

R1r

DCe/dce

Rh:1, 2, –3, 4, 5

34.9

R1R1

DCe/DCe

Rh:1, 2, –3, –4, 5

18.5

rr

dce/dce

Rh: –1, –2, –3, 4, 5

15.1

R1R2

DCe/DcE

Rh:1, 2, 3, 4, 5

13.3

R2r

DcE/dce

Rh:1, –2, 3, 4, 5

11.8

R2R2

DcE/DcE

Rh:1, –2, 3, 4, –5

2.3

r⬘r

dCe/dce

Rh: –1, 2, –3, 4, 5

0.8

r⬘r⬘

dCe/dCe

Rh: –1, 2, –3, –4, 5

Rare

r⬙r

dcE/dce

Rh: –1, –2, 3, 4, 5

0.9

r⬙r⬙

dcE/dcE

Rh: –1, –2, 3, 4, –5

Rare

R0r (R0R0)

Dce/dce(Dce/Dce)

Rh:1, –2, –3, 4, 5

2.1

r⬘r⬙ (ryr)

dCe/dcE(dCE/dce)

Rh: –1, 2, 3, 4, 5

0.05

Modified from the Blood Group Antigen Facts Book. Elsevier, San Diego, CA, 2004, p 113–114, with permission.

2682_Ch07_149-171 22/05/12 11:43 AM Page 154

154

PART II

Blood Groups and Serologic Testing

Table 7–6 Antigens of the Rh Blood Group System in Four Nomenclatures NUMERIC

FISHER-RACE

WEINER

Rh1

D

Rh0

004001

Rh2

C

rh’

004002

Rh3

E

rh’’

004003

Rh4

c

hr’

004004

Rh5

e

hr’’

004005

Rh6

ce

hr

004006

Rh7

Ce

rhi

004007

Rh8

w

C

rhw1

004008

Rh9

Cx

rhx

004009

Rh10

V

hrv

004010

Rh11

Ew

rhw2

004011

Rh12

G

rhG

004012

Rh13†

RhA

004013

Rh14

RhB

004014

Rh15†

RhC

004015

Rh16

RhD

004016

Rh17

Hr0

004017

Rh18

Hr

004018

Rh19

hrs

004019

es

004020

Rh20

VS

Rh21

CG

Rh22

CE

Rh23 Rh24†

OTHER NAMES OR COMMENT

f

ceS

HrS (High prevalence)

004021 Rh

004022

Jarvis

Dw

004023

Wiel

ET

004024

Rh25*/†

004025

Rh26

c-like

Rh27

cE

Rh28

004026

Deal

rhii

004027

hrH

004028

Hernandez

004029

Total Rh

004030

Goa (low prevalence) DIVa

Rh29 Rh30

ISBT NUMBER

cor

D

004031

Rh32

hrB = RN

004032

Troll (low prevalence)

Rh33

R0Har

004033

DHAR (low prevalence)

Rh34

HrB

004034

Bastiaan

Rh35

004035

(low prevalence)

Rh36

004036

Bea (Berrens; low prevalence)

Rh31

2682_Ch07_149-171 22/05/12 11:43 AM Page 155

Chapter 7 The Rh Blood Group System

155

Table 7–6 Antigens of the Rh Blood Group System in Four Nomenclatures—cont’d NUMERIC

FISHER-RACE

WEINER

Rh37

ISBT NUMBER 004037

Rh38†

OTHER NAMES OR COMMENT Evans (low prevalence) Formerly Duclos

Rh39

C-like

004039

Rh40

Tar

004040

Rh41

Ce-like

004041

Rh42

CeS , CceS

rhis

Targett (low prevalence)

004042

Thornton

Rh43

004043

Crawford (low prevalence)

Rh44

004044

Nou (high prevalence)

Rh45

004045

Riv

004046

Sec (high prevalence)

004047

Dav (high prevalence)

Rh48

004048

JAL (low prevalence)

Rh49

004049

Stem

Rh50

004050

FPTT (low prevalence)

Rh51

004051

MAR (high prevalence)

Rh52

004052

BARC (low prevalence)

Rh53

004053

JAHK (low prevalence)

Rh54

004054

DAK (low prevalence)

Rh55

004055

LOCR (low prevalence)

Rh56

004056

CENR (low prevalence)

Rh57

004057

CEST

Rh46 Rh47

‘’Allelic’’

= to RN

*Rh25 was formerly assigned to the LW antigen. LW is now known as LWa and is no longer considered a member of the Rh system. † Obsolete names: Rh13, Rh14, Rh15, Rh16 former classification of partial D types, Rh 24, Rh25 formerly LW, Rh38 formerly Duclos.

When referring to a gene, an allele, or a haplotype, the symbols are italicized. A haplotype is followed by a space or an asterisk, and then the numbers of the specificities are separated by commas. The R1 haplotype or DCe would be RH 1,2,5 or RH*1,2,5.

Overview of Rh Terminologies Blood bankers must be familiar with Fisher-Race, Wiener, Rosenfield, and ISBT nomenclatures and must be able to translate among them when reading about, writing about, or discussing the Rh blood group system. Tables 7–4, 7–5, and 7–6 summarize the data presented in this section. These tables also include probable genotypes based on the antigens found in selected RBC populations. Table 7–7 correlates Rh phenotypes with the most probable or predicted genotype in a designated population. Results of typing do not define genotype, only phenotype. Other

possible genotypes that can occur with the given test results are also listed, but they are not commonly seen. Determining probable or predicted genotypes was useful for parentage studies, also known as relationship testing, and for population studies. Other molecular methods are proving more powerful today. Probable genotypes are useful in predicting the potential for HDFN in offspring of Rh-negative women with anti-D; however, molecular testing, commonly referred to as zygosity testing, can be performed to confirm whether the father possesses one or two copies of the RHD gene. There are substantial differences in phenotypes and predicted genotypes of various populations. For example, the phenotype D+C-E-c+e+ is most commonly seen in the black population but is considered relatively rare in whites (see Tables 7–5 and 7–7). These differences must be remembered when trying to locate compatible blood for recipients with unusual or multiple Rh antibodies.

2682_Ch07_149-171 22/05/12 11:43 AM Page 156

156

PART II

Blood Groups and Serologic Testing

Table 7–7 Eighteen Possible Reaction Patterns With Five Antisera* OTHER POSSIBILITIES (BOTH GROUPS)

D

C

E

C

E

WHITES (%)

BLACKS (%)

WHITES

BLACKS

+

+

+

+

34.9

15

DCe/dce

DCe/Dce or DCe/dce

dCe/Dce

9 +

+

+

18.5

3

DCe/DCe

DCe/DCe

DCe/dCe

+

+

+

+

+

13.3

4

DCe/DcE

DCe/DcE

DCe/dcE, dCe/DcE, DCE/dce, DCE/Dce, or dCE/Dce

+

+

+

+

11.8

10

DcE/dce

DcE/Dce or DcE/dce

dcE/Dce

6 +

+

+

2.3

1

DcE/DcE

DcE/DcE

DcE/dcE

+

+

+

2.1

19

Dce/dce

Dce/Dce, or Dce/dce

23 –

+

+

15.1

7

dce/dce

dce/dce

+

+

+

0.8

1

dCe/dce

dCe/dce

+

+

+

0.8

rare

dcE/dce

dcE/dce

+

+

+

+

0.05%

rare

dCe/dcE

dCE/dce

+

+

rare

rare

dCe/dCe

+

+

rare

rare

dcE/dcE

+

+

+

+

0.2%

rare

DCE/DCe

DCE/dCe

+

+

+

+

0.1%

rare

DCE/DcE

DCE/dcE

+

+

+

0.1%

rare

DCE/DCE

DCE/dCE

+

+

+

rare

rare

dCE/dCe

+

+

+

rare

rare

dCE/dcE

+

+

rare

rare

dCE/dCE

*Percentages are rounded off.

To further emphasize the interchangeable use of the terminologies for the basic antigens, see Table 7–5, which defines common genotypes using the Fisher-Race, Wiener, and Rosenfield nomenclatures. Frequencies listed are for those found in the Caucasian population. Finally, as the genetics and biochemistry of the Rh blood group system have been unraveled, the terminology has continued to change. For consistency of use, RHD and RHCE, all uppercase and in italics, will be used from this point forward in the text to indicate genes. RhD, RhCe, RhcE, Rhce, and RhCE will be used to designate proteins on which the Rh antigens reside.

Molecular Genetics Several theories have been described to explain genetically the results of serologic and biochemical studies in the

Rh system. Two theories of Rh genetic control were initially postulated. Wiener hypothesized that a single gene produces a single product that contains separately recognizable factors (see Fig 7–2). In contrast, Fisher and Race proposed that the Rh locus contains three distinct genes that control production of their respective antigens (see Fig 7–1). Later, Tippett correctly proposed two RH genes, RHD and RHCE, that control expression of Rh antigens.12

RH Genes It is now known that only two closely linked genes located on chromosome 1 control expression of Rh proteins—namely, RHD and RHCE.13–15 The gene RHD codes for the presence or absence of the RhD protein, and the second gene RHCE codes for either RhCe, RhcE, Rhce, or RhCE proteins (Fig. 7–3). RHD and RHCE genes each have 10 exons and are 97% identical.

2682_Ch07_149-171 22/05/12 11:43 AM Page 157

Chapter 7 The Rh Blood Group System

157

RH Genes in Rh-Negative Caucasians

RH Genes — Rh Positive Locus 1

Locus 2

RHD

RHCE

Locus 1

Locus 2 RHCE

1 2 3 4 5 6 7 8 9 10

1 2 3 4 5 6 7 8 9 10

1 2 3 4 5 6 7 8 9 10

Exons

Exons

Exons

D antigen

C/c and E/e antigens

A

B

No D antigens

ce antigens

Figure 7–3. Locus 1 presence of RHD codes for the presence of D (A) or no D (B). Locus 2 codes for Ce, CE, cE, ce. Each gene consists of 10 coding exons.

Another gene important to Rh antigen expression is RHAG, and it resides on chromosome 6.16 The product of this gene is Rh-associated glycoprotein (RhAG). This polypeptide is very similar in structure to the Rh proteins, with the difference being it is glycosylated (carbohydrates attached). Within the RBC membrane, it forms complexes with the Rh proteins. RhAG is termed a coexpressor and must be present for successful expression of the Rh antigens. However, by itself, this glycoprotein does not express any Rh antigens. When mutations in the RHAG gene occur, it can result in missing or significantly altered RhD and RhCE proteins, affecting antigen expression. In rare instances, individuals express no Rh antigens on their RBCs. These individuals are said to have the Rhnull phenotype and are discussed in more detail later in this chapter. RHAG has been assigned as a blood group system and is discussed in further detail in Chapter 8, “Blood Group Terminology and the Other Blood Groups.”

Rh-Positive Phenotypes As predicted, RH genes are inherited as codominant alleles. Rh-positive individuals inherit one or two RHD genes, which result in expression of RhD antigen and are typed Rh-positive. In addition to the RHD gene(s), two RHCE genes are inherited, one from each parent. Figure 7–4 is an example of a normal Rh inheritance pattern. Numerous mutations in the RHD gene have been discovered that cause weakened expression of the RhD antigen detected in routine testing. This is generally termed weak D or weak expression of D and will be discussed in more detail later in the chapter.

DCe/dce

DCe/DcE

DCe/dce

DcE/dce

dce/DcE

Figure 7-4. Example of a normal pattern of Rh inheritance.

dce/dce

Rh-Negative Phenotypes Rh-negative individuals can arise from at least three different mutations. These mutations are most often found in individuals falling into three different ethnic backgrounds: European, African, and Asian. European Ethnicity Common Rh-negative white individuals have a deletion of the RHD gene—that is, they possess no RHD gene but have inherited two RHCE genes.17

Advanced Concepts African Ethnicity An unusual form of the RHD gene occurs in 66% of individuals of African ethnicity termed RHD pseudogene or RHDψ. This gene is an RHD-negative allele whose sequence is identical to the RHD gene except for missense mutations in exon 5 and exon 6, a nonsense mutation in exon 6, and a 37-bp insertion at the intron 3/exon 4 boundary.18 Individuals with this gene do not produce RhD protein. Asian Ethnicity Another mutation has been described in Asians that alters the RHD gene, causing an individual to type as D-negative.19 This is termed Del and will be discussed further in the section on weak D phenotypes. Numerous mutations have been described in the RH genes. Greater than 150 alleles have been determined in the RHD gene, and greater than 60 alleles have been found in the RHCE allele and the number continues to grow.20 Fortunately for the medical laboratory scientist, these mutations rarely change the serology observed in dayto-day testing.

Biochemistry Basic Concepts The product of RH genes are nonglycosylated proteins. This means no carbohydrates are attached to the protein. Rh antigens reside on transmembrane proteins and are an

2682_Ch07_149-171 22/05/12 11:43 AM Page 158

158

PART II

Blood Groups and Serologic Testing

integral part of the RBC membrane.21 The gene products of RHD and RHCE are remarkably similar in that both encode for proteins composed of 416 amino acids that traverse the cell membrane 12 times. Their proteins differ by only 32 to 35 amino acids.22 Amino acid position 103 is important in determining C or c expression and position 226 differentiates E from e (Fig. 7–5). Only small loops of Rh proteins are exposed on the surface of the RBC and provide the conformational requirements for many serologic differences between the Rh blood types.

Advanced Concepts In researching the biochemistry of Rh antigens, investigations have been performed to determine the quantity of antigen sites on RBCs of various Rh phenotypes. In comparison with ABO and Kell (K) blood groups, A1 cells possess approximately 1 × 106 A antigens, whereas RBCs possessing a double-dose expression of the K antigen have 6,000 K sites. Hughes-Jones and coworkers measured the number of D antigen sites on a variety of Rh phenotypes.23 The results are summarized in Table 7–8. The greatest number of D antigen sites are on cells of the rare Rh phenotype D (refer to the “Deletions” section). However, of the commonly encountered Rh genotypes, R2R2 cells possess the largest number of D antigen sites. Rh Function RhD and RhCE proteins and RhAG are exclusively on red blood cells. As they are transmembranes, it is not surprising they play a role in maintaining the structural integrity of red cells. Based on their structure, it appears they may also be transporters. Westhoff and colleagues showed they may have a role in transporting ammonia.24 An alternative hypothesis is that they may be CO2 transporters.25

Weak D: Variations of D Antigen Expression When Rh-positive RBC samples are typed for the D antigen, they are expected to show strong positive reactivity with anti-D reagents. However, some individuals have RBCs that Cell Exterior C/c

E/e

Cell Membrane

NH2

Cell Interior

COOH

Figure 7–5. Model of Rh polypeptide; “o” denotes where the sequence of D diverges from C/c or E/e. The C/c and E/e, respectively, denote the region responsible for the serologic difference between C/c and E/e.

Table 7–8 Number of D Antigen Sites of Cells with Various Phenotypes Rh PHENOTYPE

NUMBER OF D ANTIGEN SITES

R1r

9,900–14,600

R0r

12,000–20,000

R2r

14,000–16,600

R1R1

14,500–19,300

R1R2

23,000–31,000

R2R2

15,800–33,300

D--

110,000–202,000

possess D antigen that requires an indirect antiglobulin test to detect the presence of D antigen. RBCs carrying weaker D antigen have historically been referred to as having the Du type based on the original description of what the investigators thought was a new antigen.26 It was later proven that this was not a new antigen since individuals did not produce anti-Du; they produced anti-D. For many years, all individuals with altered D antigen were referred to as having weak D because their RhD antigen was altered. Now these individuals with altered D antigen are categorized into different phenotypes defined as weakened D due to C in trans to RHD, weak D, partial D, and Del. It has been shown that 1% to 2% of individuals with European ancestry possess some altered form of D antigen.27 Altered D antigen occurs more often in individuals of African descent, but the exact prevalence is not known. Finally, to further complicate matters, there are rare individuals who possess D epitopes on their RhCE protein.28,29

C in Trans to RHD The first mechanism that may result in weakened expression of D antigen was originally described as a position effect or gene interaction effect.30 The allele carrying RHD is trans (or in the opposite haplotype) to the allele carrying C; for example, Dce/dCe. The Rh antigen on the RBC is normal, but the steric arrangement of the C antigen in relationship to the D antigen appears to interfere with the expression of D antigen. This interference with D expression does not occur when the C gene is inherited in the cis position to RHD, such as DCe/dce. It is not possible to serologically distinguish genetic weak D from the position effect weak D. Molecular studies would differentiate the two types. Practically speaking, this is unnecessary because the D antigen is structurally complete. These individuals can receive D-positive RBCs with no adverse effects.

Weak D The second mechanism results from inheritance of RHD genes that code for a weakened expression of the D antigen.31

2682_Ch07_149-171 22/05/12 11:43 AM Page 159

Chapter 7 The Rh Blood Group System

The D antigens expressed appear to be complete but fewer in number. On a molecular level, mutations in the RHD gene occur, causing changes in amino acids present in the transmembrane or intracellular region of the RhD protein, thus causing conformational changes in the protein. Mutations for weak D type 1 and 2 are indicated on Figure 7–6. When these changes occur, normal RhD antigen expression is altered. Individuals with weak D phenotype rarely make anti-D, since changes in their RhD protein occur “inside” the red cell. Mutations in the RHD gene causing this altered expression have been categorized into types 1 through 53 and counting. Type 1 through 3 are the most common mutations found in individuals of European ancestory.25

Partial D The third mechanism in which D antigen expression can be weakened is when one or more D epitopes within the entire D protein is either missing or altered, termed partial D.32 Some individuals have red cells with partial-D antigen that may type weaker than expected or that may not react at all when routine procedures are used with most commercial anti-D reagents. Others have partial-D types that may show normal typing with reagent anti-D. In the early 1950s, several reports33,34 described individuals who were typed D-positive but who produced an anti-D that reacted with all D-positive samples except their own. The formation of alloanti-D by D-positive individuals required explanation. Wiener and Unger35 postulated that the D antigen is made of antigenic subparts, genetically determined, that could be absent in rare instances. If an individual lacked one (or more) pieces, or epitopes, of the total D antigen, alloantibody can be made to the missing epitope(s) if exposed to RBCs that possess the complete D antigen. This theory has become well accepted. Tippett and Sanger36 worked with RBCs and sera of partial-D individuals to classify these antigens. Their work was based on testing anti-D sera from D-positive people, with RBCs from other D-positive people who also made anti-D. This led to a method of categorizing partial D. Seven categories were recognized, designated by Roman numerals I through VII. Category I is now obsolete, and a few of the categories have been further subdivided. Weak D

Partial D

159

Normal RHD

Normal RHCE

1 2 3 4 5 6 7 8 9 10

1 2 3 4 5 6 7 8 9 10

Partial DVI 1 2 3 4 5 6 7 8 9 10

1 2 3 4 5 6 7 8 9 10

Figure 7–7. One type of partial DVI gene where three exons of RHCE gene are inserted into RHD gene.

Today, partial-D antigens can be classified on a molecular level and are attributed to hybrid genes resulting from portions of the RHD gene being replaced by portions of the RHCE gene, as shown in Figure 7–7. The resulting protein contains a portion of RhD and RhCE in various combinations, depending on the hybrid gene’s makeup. These protein changes occur external to the red cell membrane. If an individual with a hybrid RhD-RhCe-RhD protein is exposed to red blood cells possessing normal RhD protein, they will make antibody to the portion of the RhD protein they are missing.37 Anti-D made by individuals expressing partial D can cause hemolytic disease of the fetus and newborn (HDFN) or transfusion reactions, or both. Once anti-D is identified, Rh-negative blood should be used for transfusion. The identification of a person with a partial-D routinely occurs after the person begins producing anti-D unless there are discrepant Rh (D) typings. This discovery should prompt collection of additional samples to be sent to an immunohematology reference laboratory for further RhD classification.

Advanced Concepts With the advent of monoclonal antibodies and the depletion and deterioration of the available anti-D made by persons with partial-D phenotypes, Tippett and coworkers38 pursued the classification of partial-D antigens using monoclonal anti-D (MAb-D). Table 7–9 presents a summary of the partial-D categories known at the time of the study. Today, a commercial monoclonal anti-D panel is available. Although helpful, it does not define all partial D and weak D types clearly. A combination of serologic typing and molecular analysis are often required to accurately categorize partial-D types.

Exterior

Del Plasma membrane

Interior Type 1

Type 2

Figure 7–6. Three-dimensional illustrations of weak and partial D. From: Chou ST, Westhoff CM. The Rh System. In: Roback JD, Grossman BJ, Harris T, Hillyer CD, eds. Technical Manual. 17th edition. AABB, Bethesda, MD, pp. 389–410, 2011.

Del is a phenotype occurring in individuals whose red blood cells possess an extremely low number of D antigen sites that most reagent anti-D are unable to detect. Adsorbing and eluting anti-D from the individual’s red cells is often the only way to detect the D antigen. This procedure requires incubating anti-D with the RBCs in question at 37°C followed by eluting the anti-D off the adsorbed red cells. The 37°C incubation provides time for the anti-D to bind to the few D antigen sites present on these red cells. Molecular studies can detect a mutant RHD

2682_Ch07_149-171 22/05/12 11:43 AM Page 160

160

PART II

Blood Groups and Serologic Testing

Table 7–9 Epitope Profiles of Partial D Antigens REACTIONS WITH MONOCLONAL ANTI-D ANTIBODIES Cells

epD1

epD2

epD3

epD4

epD5

epD6/7

epD8

epD9

I

+

±

+

+

+

+

IIIa

+

+

+

+

+

+

+

+

IIIb

+

+

+

+

+

+

+

+

IIIc

+

+

+

+

+

+

+

+

IVa

+

+

+

+

IVb

+

+

+

Va

+

+

+

+

+

+

VI

+

+

+

VII

+

+

+

+

+

+

+

DFR

±

±

+

+

±

±

+

DBT

±

+

R0Har

±

±

+ = positive reaction; 0 = negative reaction; ± = positive with some antibodies and negative with other antibodies.

gene that alters expression of the RhD protein. This phenotype is relatively common in individuals of Asian ethnicity, occurring in 10% to 30% of that population.19 It is rare in whites.

D Epitopes on RhCE Protein Like RhD proteins that can express some RhCE protein, resulting in the partial-D phenotypes, RhCE protein can express RhD epitopes detected by some monoclonal anti-D. This can cause discrepant RhD type results with historical information on a patient or donor. There are rare individuals who possess these unusual proteins and when typed with anti-D will show positive reactivity even though the D epitope is on the RhCE protein. Examples of these unusual phenotypes include DHAR and ceCF (Crawford). R0Har, also known as DHAR, results from a hybrid gene RHCE-RHD-RHCE where only a small portion of RHD is inserted into the RHCE gene (Fig. 7–8).28 If this hybrid gene is paired with a normal RHD gene, the individual will type D Epitope on RHCE Gene — D HAR Locus 1

1 2 3 4 5 6 7 8 9 10 Exons

Figure 7–8.

DHAR

Detection of Rh Antibodies and Antigens Basic Concepts Rh antibodies are fairly straightforward to detect and identify as compared to understanding the molecular genetics and biochemistry of the Rh blood group system. Further discussion on detecting antibodies made by individuals to Rh antigens follows.

Rh Antibodies

Locus 2 RHCE

No D antigens

Rh-positive. However, if paired with a D-deletion, they may type D-positive, depending on the anti-D reagent being used. These individuals should be classified as RhD-negative since they essentially lack the RhD protein. The Crawford (ceCF) phenotype is found in individuals of African descent. It results from a specific amino acid change in the RHce gene, resulting in an RhD epitope on the Rhce protein.29

ce antigens

results from one RHD exon inserted into the RHCE gene.

Although the Rh system was first recognized by saline tests used to detect IgM antibodies, most Rh antibodies are IgG immunoglobulins and react optimally at 37°C or after antiglobulin testing in any method used for antibody detection. Rh antibodies are usually produced following exposure of the individual’s immune system to foreign RBCs, through either transfusion or pregnancy. Rh antibodies may show dosage, reacting preferentially with RBCs possessing double-dose Rh antigen. For example, anti-E may show 3+ positive reactivity

2682_Ch07_149-171 22/05/12 11:43 AM Page 161

Chapter 7 The Rh Blood Group System

with E+e- RBCs versus 2+ positive reactivity with E+e+ RBCs. In addition, Rh antibodies are enhanced when testing with enzyme-treated RBCs. Rh antigens are highly immunogenic; the D antigen is the most potent.39 This is not surprising given that most Rh-negative individuals lack the entire RhD protein, resulting in a difference of 32 to 35 amino acids.22 Exposure to less than 0.1 mL of Rh-positive RBCs can stimulate antibody production in an Rh-negative person. While the D antigen is most immunogenic, c antigen is the next most likely Rh antigen to elicit an immune response, followed by E, C, and e. It is not uncommon to see several Rh antibodies in a patient; for example, anti-D and anti-C or anti-c and anti-E (see Case Study 7-2 and Figure 7-9). IgG1, IgG2, IgG3, and IgG4 subclasses of Rh antibodies have been reported. IgG1 and IgG3 are of the greatest clinical significance because the reticuloendothelial system rapidly clears RBCs coated with IgG1 and IgG3 from the circulation. IgA Rh antibodies have also been reported but are not routinely tested for in the blood bank.35 As with most blood group antibodies, IgM Rh antibodies are formed initially, followed by a transition to IgG. Rh antibodies often persist in the circulation for years. An individual with low-titer Rh antibody may experience an anamnestic (secondary) antibody response if exposed to the same sensitizing antigen. Therefore, in the clinical setting, accuracy of D typing is essential, as is the careful checking of patient history to determine whether an Rh antibody has been identified previously. Most commonly found Rh antibodies are considered clinically significant. Therefore, antigen-negative blood must be provided to any patient with a history of Rh-antibody sensitization, whether the antibody is currently demonstrable or not. Rh antibodies do not bind complement. For complement to be fixed (or the complement cascade activated), two IgG immunoglobulins must attach to an RBC antigen in close proximity to each other. Rh antigens (to which the antibody would attach) are not situated on the RBC surface this closely. Therefore, when an Rh antibody coats the RBCs, intravascular, complement-mediated hemolysis does not occur. RBC destruction resulting from Rh antibodies is primarily extravascular. However, a few rare examples of complement binding Rh antibodies have been reported. Because Rh antibodies are primarily IgG and can traverse the placenta and because Rh antigens are well developed early in fetal life, Rh antibodies formed by Rh-negative pregnant women cross the placenta and may coat fetal RBCs that carry the corresponding antigen. This results in the fetal cells having a positive direct antiglobulin test; in HDFN, the coated fetal cells are removed prematurely from the fetal circulation (see Chapter 19, “Hemolytic Disease of the Fetus and Newborn [HDFN]”). Until the discovery of Rh immune globulin, anti-D was the most frequent cause of HDFN. D

>

c

>

E

>

C

Figure 7–9. Immunogenicity of common Rh antigens.

>

e

161

Rh Typing Reagents Reagents used to type for D and for the other Rh antigens may be derived from a variety of sources. The reagents may be high-protein-based or low-protein-based, saline-based, chemically modified, monoclonal, or blends of monoclonals. The goal is to use a reagent anti-D that will allow for typing individuals’ RBCs as quickly and accurately as typing for ABO. Saline reactive reagents, which contain IgM immunoglobulin, were the first typing reagents available to test for the D antigen. Saline anti-D has the advantage of being lowprotein-based and can be used to test cells that are already coated with IgG antibody, as in patients who have warm autoantibodies binding to their RBCs. If a high-protein-based reagent was used when typing these antibody-coated RBCs, a false-positive reaction would be obtained because the RBCs would agglutinate on their own without the addition of anti-D. The primary disadvantages of saline typing reagents are their limited availability, cost of production, and lengthy incubation time. Because saline anti-D is an IgM immunoglobulin, it cannot be used for weak-D typing. In the 1940s, high-protein anti-D reagents were developed that consisted primarily of IgG anti-D. Human plasma containing high-titer D-specific antibody was used as the raw material. Potentiators of bovine albumin and macromolecular additives such as dextran or polyvinylpyrrolidone were added to the source material to optimize reactivity in the standard slide and rapid tube tests to allow for direct agglutination of red cells using an IgG anti-D.40 In essence, this media causes RBCs to be in closer proximity to each other and allows IgG anti-D to crosslink and cause direct agglutination. These reagents are commonly referred to as high-protein reagents. However, the presence of potentiators and the higher protein concentration increase the likelihood of false-positive reactions. To assess the validity of the high-protein Rh typing results, a control reagent was manufactured and had to be tested in parallel with each Rh test. If the control reacted, the test result was invalid and had to be repeated using a different technique or reagent anti-D. The major advantages of high-protein anti-D reagents are reduced incubation time and the ability to perform weak-D testing and slide typing with the same reagent. This type of anti-D reagent is also polyspecific. More than one clone of anti-D is produced by immunized human donors and is therefore able to recognize multiple epitopes on the RhD protein. In the late 1970s, scientists chemically modified the IgG anti-D molecule by breaking the disulfide bonds that maintain the antibody’s rigid shape.41 This allows the antibody to relax and to span the distance between RBCs in a low-protein medium. The chemically modified reagents can be used for both slide and tube testing and do not require a separate, manufactured Rh control as long as the samples type as A, B, or O. When samples test AB Rh-positive or when the Rh test is performed by itself, a separate saline control or 6% to 8% albumin control must be used to ensure the observed reactions are true agglutination and not a result of spontaneous agglutination. Fewer false-positive test reactions are obtained

2682_Ch07_149-171 22/05/12 11:43 AM Page 162

162

PART II

Blood Groups and Serologic Testing

because of the lower-protein suspending medium. Because of its lower-protein base and ready availability, the chemically modified anti-D replaced the need for saline (IgM) anti-D reagents. As monoclonal antibody production became available, Rh monoclonal antibodies were produced. These reagents are derived from single clones of antibody-producing cells. The antibody-producing cells are hybridized with myeloma cells to increase their reproduction rate, thereby maximizing their antibody-producing capabilities. Because the D antigen is composed of many epitopes and the monoclonal Rh antibodies have a narrow specificity, monoclonal anti-D reagents are usually a combination of monoclonal anti-D reagents from several different clones to ensure reactivity with a broad spectrum of Rh-positive RBCs. Some companies also blend IgM and IgG anti-D to maximize visualization of reactions at immediate spin testing and to allow indirect antiglobulin testing for weak D antigen with the same reagent.42 Monoclonal blends can be used for slide, tube, microwell, and most automated Rh testing. Because these reagents are not human-derived, they lack all potential for transmitting infectious disease. As with all commercial typing reagents, Rh antigen typing must be performed with strict adherence to manufacturer’s directions, use of proper controls, and accurate interpretation of test and control results. Table 7–10 summarizes several

common causes of false Rh typing results and suggests corrective actions that may be taken to obtain an accurate Rh type.

Clinical Considerations Determining an individual’s RhD type and testing to identify antibodies to Rh antigens has been reviewed. When Rh antibodies are identified it is important to understand the clinical implications when Rh incompatibility exists.

Transfusion Reactions Rh antigens are highly immunogenic. The D antigen is the most immunogenic antigen outside the ABO system. When anti-D is detected, a careful medical history will reveal RBC exposure through pregnancy or transfusion ofproducts containing RBCs. Circulating antibody appears within 120 days of a primary exposure and within 2 to 7 days after a secondary exposure. Rh-mediated hemolytic transfusion reactions, whether caused by primary sensitization or secondary immunization, usually result in extravascular destruction of immunoglobulincoated RBCs. The transfusion recipient may have an unexplained fever, a mild bilirubin elevation, and a decrease in hemoglobin and haptoglobin. The direct antiglobulin test

Table 7–10 False Reactions With Rh Typing Reagents FALSE-POSITIVES

FALSE-NEGATIVES

Likely Cause

Corrective Action

Likely Cause

Corrective Action

1. Cell suspension too heavy

1. Adjust suspension, retype

1. Immunoglobulin-coated cells (in vivo)

1. Use saline-active typing reagent

2. Cold agglutinins

2. Wash with warm saline, retype

2. Saline-suspended cells (slide)

2. Use unwashed cells

3. Test incubated too long or drying (slide)

3. Follow manufacturer’s instructions precisely

3. Failure to follow manufacturer’s directions precisely

3. Review directions; repeat test

4. Rouleaux

4. Use saline-washed cells, retype

4. Omission of reagent manufacturer’s directions

4. Always add reagent first and check before adding cells

5. Fibrin interference

5. Use saline-washed cells, retype

5. Resuspension too vigorous

5. Resuspend all tube tests gently

6. Contaminating low-incidence antibody in reagent

6. Try another manufacturer’s reagent or use a known serum antibody

6. Incorrect reagent selected

6. Read vial label carefully; repeat

7. Polyagglutination

7. See chapter on polyagglutination

7. Variant antigen

7. Refer sample for further investigation

8. Bacterial contamination of reagent vial

8. Open new vial of reagent, retype

8. Reagent deterioration

8. Open new vial

9. Incorrect reagent selected

9. Repeat test; read vial label carefully

10. Centrifugation too long

10. Repeat test using shorter centrifugation time

10. Centrifugation too short

10. Repeat test using longer centrifugation time

11. rpm too high

11. Repeat test using lower rpm

11. rpm too low

11. Repeat testing using higher rpm

2682_Ch07_149-171 22/05/12 11:43 AM Page 163

Chapter 7 The Rh Blood Group System

is usually positive, and the antibody screen may or may not demonstrate circulating antibody. When the direct antiglobulin test indicates that the recipient’s RBCs are coated with IgG, elution studies may be helpful in defining the offending antibody specificity. If antibody is detected in either the serum or eluate, subsequent transfusions should lack the implicated antigen. It is not unusual for a person with a single Rh antibody to produce additional Rh antibodies if further stimulated.39

Hemolytic Disease of the Fetus and Newborn Hemolytic disease of the fetus and newborn (HDFN) is briefly described here because of the historic significance of the discovery of the Rh system in elucidating its cause; it is covered in more detail in Chapter 19. As stated previously, anti-D was discovered in a woman after delivery of a stillborn fetus. The mother required transfusion. The baby’s father donated blood for the transfusion, and the mother subsequently experienced a severe hemolytic transfusion reaction. Levine and Stetson1 postulated that the antibody causing the transfusion reaction also crossed the placenta and destroyed the RBCs of the fetus, causing its death. The offending antibody was subsequently identified as anti-D.3 HDFN caused by Rh antibodies is often severe because the Rh antigens are well developed on fetal cells, and Rh antibodies are primarily IgG, which readily cross the placenta. After years of research, a method was developed to prevent susceptible (D-negative) mothers from forming anti-D, thus preventing RhD HDFN. Rh-immune globulin, a purified preparation of IgG anti-D, is given to D-negative woman during pregnancy and following delivery of a D-positive fetus.43 Rh-immune globulin is effective only in preventing RhD HDFN. No effort has been made to develop immune globulin products for other Rh antigens (e.g., C, c, E, e). When present, Rh HDFN may be severe and may require aggressive treatment. Refer to Chapter 19 for a more detailed discussion of HDFN—its etiology, serology, and treatment.

Rh Deficiency Syndrome: Rhnull and Rhmod Rare individuals have Rh deficiency or Rhnull syndrome and fail to express any Rh antigens on the RBC surface. This syndrome is inherited in one of two ways—amorphic and regulator. Other rare individuals exhibit a severely reduced expression of all Rh antigens, a phenotype called Rhmod. Individuals who lack all Rh antigens on their RBCs are said to have Rhnull syndrome, which can be produced by two different genetic mechanisms.37 In the regulator-type Rhnull syndrome, a mutation occurs in the RHAG gene. This results in no RhAG protein expression and subsequently no RhD or RhCE protein expression on the RBCs, even though these individuals usually have a normal complement of RHD and RHCE genes. These individuals can pass normal RHD and RHCE genes to their children.

163

In the second type of Rhnull syndrome (the amorphic type), there is a mutation in each of the RHCE genes inherited from each parent and the common deletion of the RHD gene found in most D-negative individuals. The RHAG gene is normal. It should be noted that Rhnull individuals of either regulator or amorphic type are negative for the high prevalence antigen LW and for FY5, an antigen in the Duffy blood group system. S, s, and U antigens found on glycophorin B may be depressed.44 Individuals with Rhnull syndrome demonstrate a mild compensated hemolytic anemia,45 reticulocytosis, stomatocytosis, a slight-to-moderate decrease in hemoglobin and hematocrit levels, an increase in hemoglobin F, a decrease in serum haptoglobin, and possibly an elevated bilirubin level. The severity of the syndrome is highly variable from individual to individual, even within one family. When transfusion of individuals with Rhnull syndrome is necessary, only Rhnull blood can be given. Individuals of the Rhmod phenotype have a partial suppression of RH gene expression caused by mutations in the RHAG gene. When the resultant RhAG protein is altered, normal Rh antigens are also altered, often causing weakened expression of the normal Rh and LW antigens. Rhmod RBCs exhibit other blood group antigens; however, like Rhnull, S, s, and U antigen expression may be depressed.45 Rhmod individuals exhibit features similar to those with the Rhnull syndrome; however, clinical symptoms are usually less severe and rarely clinically remarkable.46

Unusual Phenotypes and Rare Alleles Several of the less frequently encountered Rh antigens are described briefly in the following paragraphs. Refer to other textbooks for in-depth discussions.28,47–49

Cw Cw was originally considered an allele at the C/c locus.50 Later studies showed that it can be expressed in combination with both C and c and in the absence of either allele. It is now known that the relationship between C/c and Cw is only phenotypic and that Cw is antithetical to the high-prevalence antigen MAR.51 Cw results in a single amino acid change most often found on the RhCe protein. Cw is found in about 2% of whites and is very rare in blacks. Anti-Cw has been identified in individuals without known exposure to foreign RBCs and after transfusion or pregnancy. Anti-Cw may show dosage (i.e., reacting more strongly with cells from individuals who are homozygous for Cw). Because of the low prevalence of Cw, Cw antigen–negative blood is readily available.

f (ce) The f antigen is expressed on the RBC when both c and e are present on the same haplotype; it has been called a

2682_Ch07_149-171 22/05/12 11:43 AM Page 164

164

PART II

Blood Groups and Serologic Testing

compound antigen.52 However, f is likely a single entity resulting from conformational changes in the Rhce protein.53 The antigen f was included in a series of these compound antigens, which were previously referred to as cis-products to indicate that the antigens were on the same haplotype. It is now known they are expressed on the Rhce protein. Phenotypically, the following samples appear the same when tested with the five major Rh antisera: D+C+E+c+e+, resulting in the predicted genotypes of DCE/dce or DcE/DCe. However, when tested with anti-f, only the DCE/dce shows positive reactivity, confirming the former genotype. Anti-f is generally a weakly reactive antibody often found with other antibodies. It has been reported to cause HDFN and transfusion reactions. In case of transfusion, f-negative blood should be provided. Anti-f is not available as a reagent; however c-negative or e-negative blood may be provided since all c-negative or e-negative individuals are f-negative.

rhi (Ce) Similar to f, rhi was considered a compound antigen present when C and e are on the RhCe protein.52 A sample with the phenotype D +C +E +c +e + can be either DcE/DCe or DCE/dce. Anti-rhi shows positive reactivity only with DCe/dce RBCs. Antigens cE and CE or Rh22 also exist, but antibodies produced to these antigens are not commonly seen.

G G is an antigen present on most D-positive and all C-positive RBCs. The antigen results from the amino acid serine at position 103 on the RhD, RhCe, and RhCE protein. In antibody identification testing, anti-G reacts as though it were a combination of anti-C plus anti-D because all C-positive and D-positive cells are G+.54 G was originally described in an rr person who received D+C–E–c+e+ RBCs. Subsequently, the recipient produced an antibody that appeared to be anti-D plus anti-C, which should be impossible because the C antigen was not on the transfused RBCs. Further investigation showed the antibody was directed toward D + G, not anti-C. This also explains situations in which an Rh-negative individual who has received Rh-negative blood will look like they made anti-D. The Rh-negative blood the patient received was C-positive, thus G-positive and the antibody produced is actually anti-G, not anti-D and anti-C. Anti-G versus anti-D and anti-C is important when evaluating obstetric patients. If the patient has produced anti-G and not anti-D, they are considered a candidate for RhIg. Elaborate adsorption and elution studies, usually performed in an immunohematology reference laboratory, are valuable in these situations to discriminate anti-D from anti-C from anti-G. For transfusion purposes, it is not necessary to discriminate anti-D and anti-C from anti-G, as the patient would receive D-C blood regardless if the antibody is –D, –C or –G.

Rh13, Rh14, Rh15, and Rh16 Advanced Concepts Rh13, Rh14, Rh15, and Rh16 define four different parts of the D mosaic, as it was originally described.55 Although these parts are included in the partial-D categories II to VII as defined by Tippett and Sanger,36 they are not directly comparable. These antigens are now obsolete. Rh17 (Hr0) Rh17, also known as Hr0, is an antigen present on all RBCs with the “common” Rh phenotypes (e.g., R1R1, R2R2, rr).56 In essence, this antibody is directed to the entire protein resulting from the RHCE genes. When RBCs phenotype as D–, the most potent antibody they make is often one directed against Rh17 (Hr0).

Rh23, Rh30, and Rh40 Rh23, Rh30, and Rh40 are all low-prevalence antigens associated with a specific category of partial-D. These low-prevalence antigens result from the formation of the hybrid proteins seen in individuals with partial-D phenotypes. Rh23 (also known as Wiel and Dw) is an antigenic marker for category Va partial-D.57 Rh30 (also known as Goa or Dcor) is a marker for partial DIVa.58 Rh40 (also known as Tar or Targett) is a marker for partial DVII.59 Rh52 or BARC is associated with some partial-DVI types.36

Rh33 (Har) The low-prevalence antigen Rh33 is most often found in whites and is associated with the rare variant haplotype called R0Har.60 R0Har gene codes for normal amounts of c, reduced amounts of e, reduced f, reduced Hr0, and reduced amounts of D antigen written as (D)c(e). The D reactions are frequently so weak that the cells are often typed as Rh-negative. As previously discussed, R0Har or DHAR results from a hybrid gene RHCE-RHD-RHCE in which only a small portion of RHD is inserted into the RHCE gene.

Rh32 Rh:32 is a low-prevalence antigen associated with a variant = of the R1[D(C)(e)] haplotype called RN.61 The C antigen and e antigen are expressed weakly. The D antigen expression is exaggerated or exalted. This gene has been found primarily in blacks.

Rh43 (Crawford) Rh43, also known as the Crawford antigen, is a low-prevalence antigen on a variant Rhce protein.29 The Crawford (ceCF) antigen is of very low prevalence found in individuals of African descent.

2682_Ch07_149-171 22/05/12 11:43 AM Page 165

Chapter 7 The Rh Blood Group System

e Variants Like the variant D antigen seen in individuals possessing a hybrid or mutated RHD gene, some individuals of African or mixed ethnic backgrounds possess e antigen that exhibits similar qualities as those described for partial-D phenotypes— that is, an individual may phenotype e-positive but produce antibodies behaving as anti-e.62 These variant types result from multiple mutations in the RHCE gene.63 Individuals who possess two altered RHCE genes may phenotype e-positive but produce antibodies behaving as anti-e. The Rh antigens hrB and hrS are rarely considered in routine blood banking. They are normally present in individuals who possess normal RhCe or Rhce protein but are lacking in individuals with normal RhcE or RhCE proteins (i.e., e-negative). Several antigens, most notably hrB and hrS, are lacking on the resulting Rhce proteins encoded by some variant RHCE genes. If individuals with these variant genes who are hrB-negative or hrS-negative are immunized, they may produce anti-hrB or anti-hrS. In routine antibody identification, these antibodies are generally nonreactive with e-negative red cells (and therefore are also hrB-negative and hrS-negative), appearing to have anti-e-like specificity. To further complicate this, the variant RHCE gene associated with the hrB-negative phenotype is usually found with a variant RHD-CE-D hybrid gene. The RHCE is inserted in the middle of the RHDIIIa gene. The resulting protein lacks D antigen but possesses an unusual form of the C antigen. The hybrid gene occurs in 22% of individuals of African decent.18,64 This haplotype that includes the RHDIIIa-RHCEDIIIa hybrid gene and variant RHCE genes is referred to as r’s[(C)ces].

V and VS V and VS are antigens of low prevalence in the Caucasian population but are more prevalent among African Americans. These antigens can be used as predictors of an individual’s ethnic background because of this difference in prevalence. The V antigen, also historically referred to as ceS,65 is found in about 30% of randomly selected African Americans. It is most often found in individuals with Gly263 amino acid change in Rhce; several other mutations also occur in this gene. The VS antigen, also known as eS, occurs in 32% in blacks.66 It results from a single amino acid change that occurs at position Val245 in the Rhce protein. Most hrB- individuals with r’s genotype are VS+. The Val245 mutation in this haplotype is found in the hybrid RHDIIIa-RHCE-RHDIIIa gene described previously.67 Most V+ individuals are also VS+.

Deletions There are very uncommon phenotypes that demonstrate no Cc and/or Ee reactivity. Many examples lacking all Cc or Ee often have an unusually strong D antigen expression,

165

frequently called exalted D. The deletion phenotype is indicated by the use of a dash (–), as in the following example: D–. This phenotype results from individuals possessing normal RHD gene(s) and hybrid RHCE-RHDRHCE in which the Rhce protein is replaced with RhD. This helps explain the exalted D, as there are extra D antigens recognized on the resulting hybrid protein. The antibody made by D–/D– people is called anti-Rh17 or anti-Hr0.49 A variation has been recognized within the deletion D–, called D••. The D antigen in the D•• is stronger than that in DC–, or Dc– samples but weaker than that of D– samples. A low-prevalence antigen called Evans (Rh:37) accompanies the Rh structure of D•• cells.68 Some deletion phenotypes are missing E/e only and are indicated as Dc- or DC-. To date, a deletion of only C/c has not been reported. Transfusion of individuals with a D– or D•• phenotype is difficult, as blood of a similar phenotype or even the rarer Rhnull blood, all lacking Rh17, would be required.

Landsteiner Weiner Blood Group System Basic Concepts A discussion of the Landsteiner Weiner (LW) antigen begins with the time when Rh antigens were first recognized. The antibody produced by injecting rhesus monkey RBCs into guinea pigs and rabbits was identified as having the same specificity as the antibody Levine and Stetson1 described earlier. The antibody was given the name anti-Rh, for anti-rhesus, and the blood group system was established. Many years later, it was recognized that the two antibodies were not identical; the anti-rhesus described by Landsteiner and Wiener2 was renamed anti-LW in their honor. Phenotypically, there is a similarity between the Rh and LW systems. Anti-LW reacts strongly with most D-positive RBCs, weakly with Rh-negative RBCs (and sometimes not at all), and never with Rhnull cells. AntiLW usually shows stronger positive reactivity with D-positive RBCs than with D-negative adult RBCs. A weak anti-LW may be positive only with D-positive RBCs, and enhancement techniques may be required to demonstrate its reactivity with D-negative cells. Anti-LW shows equal reactivity with cord cells regardless of their D type.69 This is an important characteristic to remember when trying to differentiate anti-LW from anti-D. Also, anti-LW more frequently appears as an autoantibody, which does not present clinical problems. Further discussion can be found in Chapter 8, “Blood Group Terminology and the Other Blood Groups.” Because of the complexity of the Rh blood group system, a tremendous amount of literature exists. The inquisitive reader can continue to piece together the puzzle by consulting the sources included in the references.

2682_Ch07_149-171 22/05/12 11:43 AM Page 166

166

PART II

Blood Groups and Serologic Testing

CASE STUDIES Case 7-1 Two units of blood are ordered for an 89-year-old woman with myelodysplastic syndrome. She had been transfused 3 years ago and has six children. Routine pretransfusion testing follows. Anti-A 0

Anti-B 0

Anti-D 0

A1 Cells 4+

B Cells 4+

Interpretation

1. What is the patient’s ABO, Rh type? D 1 + 2 +

Rh E c 0 0 + +

C + 0

E + 0

f 0 0

M + +

MNS N S + + 0 +

s + 0

LU Lua Lub 0 + 0 +

P P1 + +

Lewis Lea Leb + 0 0 +

Kell K k + + 0 +

Duffy Fya Fyb + 0 + +

Kidd Jka Jkb 0 + + 0

GEL IAT 2+ 2+

2. How would you interpret the results of the antibody detection test/screen? 3. What information can you obtain from your evaluation of the antibody detection test/screen? 4. What additional testing should be performed? Rh 1 2 3 4 5 6 7 8 9 10 11 AC

D + 0 0 + 0 0 + 0 + + +

C + 0 0 + 0 + 0 0 + 0 0

E 0 0 + 0 + 0 + 0 0 + 0

c 0 + + 0 + 0 + + + + +

e + + 0 + + + 0 + + 0 +

f 0 + 0 0 + 0 0 + + 0 +

M + + 0 + + + 0 + + 0 0

MNS N S + + 0 + + 0 0 + + 0 + 0 + 0 0 + + 0 + + + 0

Gel Antibody Identification Panel Lu P1 Lewis s Lua Lub P1 Lea Leb + 0 + 0 + 0 0 0 + + 0 + + 0 + + 0 + + 0 + 0 0 0 + 0 + 0 0 + + 0 + + 0 + + 0 + 0 0 + 0 0 + + 0 + + 0 + + + 0 + 0 + + + 0 0 0 + + 0 +

Kell K k 0 + + 0 + + 0 + 0 + + + 0 + 0 + 0 + 0 + 0 +

Duffy Fya Fyb 0 + + + + 0 + + 0 + + + 0 + + 0 0 + + 0 0 0

Kidd Jka Jkb 0 + + 0 0 + + + 0 + + + + 0 0 + + 0 + 0 + +

IAT 2+ 0 0 2+ 0 0 2+ 0 2+ 2+ 2+ 0

NOTE: In this case study, antibodies are excluded only if the patient’s serum does not react with panel cells that possess a double-dose expression of the antigen (from a donor with homozygous expression). 5. What antibody(ies) is(are) present in the patient’s plasma? Case 7-2 A 25-year-old woman, pregnant with her second child, had routine orders for a “type and screen,” with the following results: Anti-A 0

Anti-B 0

Anti-D 3+

A1 Cells 4+

B Cells 4+

Interpretation

1. How would you interpret the results of the ABO, Rh type and antibody detection test (screen)?

1 2

D C + + + 0

E 0 +

Rh c 0 +

E + 0

f 0 0

M + +

NH = No hemolysis observed

MNS N S s + + + 0 + 0

LU Lua Lub 0 + 0 +

P P1 + +

Lewis Lea Leb + 0 0 +

Kell K k + + 0 +

Duffy Fya Fyb + 0 + +

Kidd Jka Jkb 0 + + 0

IS 0 0 0

37C PEG NH IAT NH 0 NH 3+

2682_Ch07_149-171 22/05/12 11:43 AM Page 167

Chapter 7 The Rh Blood Group System

167

An antibody identification panel is set up and results follow. D 1 + 2 0 3 0 4 + 5 0 6 0 7 + 8 0 9 + 10 + 11 + AC

Rh E 0 0 + 0 + 0 + 0 0 + 0

C + 0 0 + 0 + 0 0 + 0 0

c 0 + + 0 + 0 + + + + +

e + + 0 + + + 0 + + 0 +

f 0 + 0 0 + 0 0 + + 0 +

MNS N S + + 0 + + 0 0 + + 0 + 0 + 0 0 + + 0 + + + 0

M + + 0 + + 0 0 + + 0 0

Lu Lua 0 0 0 0 0 0 0 0 0 0 0

s + 0 + 0 + + + 0 + + 0

P1 Lewis P1 Lea Leb 0 + 0 + 0 + + 0 + 0 0 0 0 0 + + 0 + 0 0 + + 0 + + + 0 + + 0 + 0 +

Lub + + + + + + + + + + +

Kell K k 0 + + 0 + + 0 + 0 + + + 0 + 0 + 0 + 0 + 0 +

Duffy Fya Fyb 0 + + + + 0 + + 0 + + 0 0 + + 0 0 + + 0 0 0

Kidd Jka Jkb 0 + + 0 0 + + + 0 + + 0 + 0 0 + + 0 + 0 + +

IS 0 0 0 0 0 0 0 0 0 0 0 0

PEG 37C NH NH NH NH NH NH NH NH NH NH NH NH

IAT 0 3+ 3+ 0 3+ 0 3+ 3+ 3+ 3+ 3+ 0

NOTE: In this case study, antibodies are excluded only if the patient’s serum does not react with panel cells that possess a double-dose expression of the antigen (from a donor with homozygous expression). 2. What antibody(ies) cannot be ruled out based on the panel results? 3. What additional testing should be performed? The patient was phenotyped for the following antigens: Patient 4. 5. 6. 7.

Anti-C 4+

Anti-E 0

Anti-c 0

Anti-e 4+

Anti-K 4+

Using Fisher-Race and Weiner nomenclature, what are the possible Rh phenotypes? Using Fisher-Race and Weiner nomenclature, what is the most probable genotype? Does the patient’s antigen type confirm or conflict with your antibody identification? Which Rh antibodies are difficult to rule out on a double-dose (homozygous) antigen-positive cell in this case? Explain why.

Case 7-3 (Advanced) A 29-year-old female, pregnant for the first time, presented to her OB physician in her early first trimester for initial prenatal care. She had no known prior transfusions. Anti-A 4+

Forward Anti-B 0

Anti-D 0

A1 0

Reverse B Interpretation 4+

1. What is the patient’s ABO, Rh type?

1 2

D + +

C + 0

E 0 +

Rh c 0 +

E + 0

F 0 0

M + +

MNS N S + + 0 +

s + 0

LU Lua 0 0

Lub + +

P P1 + +

Lewis Kell Lea Leb K k + 0 + + 0 + 0 +

Duffy Fya Fyb + 0 + +

Kidd Jka Jkb 0 + + 0

GEL IAT 0 0

Approximately 1 month later, the Transfusion Service received a call from the OB physician, stating the patient had been previously typed as “A-positive” at another facility and her donor card states “A-positive.” A sample is sent to the laboratory for repeat ABO, Rh typing. The patient’s repeat ABO, Rh type showed the same results: A Rh-negative. Because of the reported discrepancy, the patient’s Rh (D) typing was performed using several different anti-D reagents.

2682_Ch07_149-171 22/05/12 11:43 AM Page 168

168

PART II

Blood Groups and Serologic Testing

Results with various anti-D reagents are as follows: Anti-D Reagent G-clone (monoclonal) O-clone (monoclonal) Gel IgG (polyspecific—human) Polyspecific—human

IS 0 0 0

IAT 4+ 3+ 0 3+

Control IAT 0 0 0 0

Typing with different anti-D reagents showed variability. All required a weak D test or indirect antiglobulin test to detect the weakened D antigen. The Rh typing was reported as follows: A-negative—for transfusion purposes and candidacy for RhIG at the testing facility, patient is considered “Rh(D)-negative” (patient to receive Rh[D]-negative blood products and RhIG prophylaxis recommended). Further testing was performed to determine if the patient possessed a partial-D antigen. The Rh phenotype results follow: Patient Positive control Negative control

Anti-C 3+ 4+ 0

Anti-E 0 4+ 0

Anti-c 4+ 4+ 0

Anti-e 4+ 4+ 0

2. Using Fisher-Race and Weiner nomenclature, what are the possible Rh phenotypes? 3. Using Fisher-Race and Weiner nomenclature, what is the most probable genotype? The sample was sent to an immunohematology reference laboratory for further characterization. A commercial monoclonal anti-D panel was available for testing to aid in differentiating weak D from partial D. The patient’s RBCs were typed with this kit. Anti-D Expected patterns of reactivity of different forms of partial D with the different monoclonal anti-D antibodies Test Results Cell Line Weak D DHK type 1 DII and and and DAR- DAUPOS Neg 2 DNU DIII DIV DV DCS DVI DVII DOL DFR DMH DAR E 4 DBT RoHar Cont Cont LHM + + + + +/0 + 0 + + + + + 0 0 0 (+)/0 4 0 76/58 LHM + + + 0 + + + + + + + + + + 0 0 4 0 76/59 LHM (+) + + 0 0 + 0 + 0 0 + 0 0 0 0 0 4 0 174/102 /0 LHM + + + + + + 0 + + + + + + + 0 0 4 0 50/28 LHM + + + 0 0 + 0 + + + + 0 0 0 0 0 4 0 169/81 ESDI + + + 0 + + + + + + + + + + 0 0 4 0 LHM + + + 0 + + + + + + + + + + 0 0 4 0 76/55 LHM + 0 + 0 + + + + + + + + + +/0 0 0 4 0 77/64 LHM (+) + + 0 0 0 0 + 0 0 0 0 0 0 0 0 4 0 70/45 /0 LHM + + + + + + 0 0 0 0 0 0 (+) + + 0 4 0 59/19 LHM + + + + + + 0 + + + + + + 0 0 0 4 0 169/80 LHM + + + + + 0 0 + + 0 + + + 0 + 0 4 0 57/17

Pt 0 3+ 0 0 0 4+ 3+ 3+ 0 0 0 0

The results are consistent with a partial DVI. Discrepancies in RhD typing are dependent on reagents and methods used to detect RhD antigen.

2682_Ch07_149-171 22/05/12 11:43 AM Page 169

Chapter 7 The Rh Blood Group System

169

SUMMARY CHART

  

 

The Rh antibody was so named on the basis of antibody production by guinea pigs and rabbits when transfused with rhesus monkey RBCs. Historically, Rh was a primary cause of HDFN, erythroblastosis fetalis, and a significant cause of hemolytic transfusion reactions. Fisher-Race DCE terminology is based on the theory that antigens of the system are produced by three closely linked sets of alleles and that each gene is responsible for producing a product (or antigen) on the RBC surface. A person who expresses no Rh antigens on the RBC is said to be Rhnull, and the phenotype may be written as –––/–––. In the Wiener Rh-Hr nomenclature, it is postulated that the gene responsible for defining Rh actually produces an agglutinogen that contains a series of blood factors in which each factor is an antigen recognized by an antibody. It is currently accepted that two closely linked genes control the expression of Rh; one gene (RHD) codes for the presence of RhD, and a second gene (RHCE) codes for the expression of CcEe antigens. In the Rosenfield alpha/numeric terminology, a number is assigned to each antigen of the Rh system

Review Questions 1. The Rh system was first recognized in a case report of: a. b. c. d.

A hemolytic transfusion reaction. Hemolytic disease of the fetus and newborn. Circulatory overload. Autoimmune hemolytic anemia.

2. What antigen is found in 85% of the white population

and is always significant for transfusion purposes? a. d b. c c. D d. E 3. How are weaker-than-expected reactions with anti-D

typing reagents categorized? a. Rhmod b. Weak D c. DAT positive d. Dw 4. Cells carrying a weak-D antigen require the use of what

test to demonstrate its presence? a. Indirect antiglobulin test b. Direct antiglobulin test c. Microplate test d. Warm autoadsorption test

   

 

in order of its discovery (Rh1 = D, Rh2 = C, Rh3 = E, Rh4 = c, Rh5 = e). Rh antigens are characterized as nonglycosylated proteins in the RBC membrane. The most common phenotype in whites is R1r (31%); the most common phenotype in blacks is R0r (23%), followed by R0R0 at 19%. The Rh antigens are inherited as codominant alleles. A partial-D individual is characterized as lacking one or more pieces or epitopes of the total D antigen and may produce alloantibody to the missing fraction if exposed to RBCs with the complete D antigen. Blood donor units for transfusion are considered Rh-positive if either the D or weak-D test is positive; if both the D and weak-D tests are negative, blood for transfusion is considered Rh-negative. Most Rh antibodies are IgG immunoglobulin and react optimally at 37°C or following antiglobulin testing; exposure to less than 0.1 mL of Rh-positive RBCs can stimulate antibody production in an Rh-negative person. Rh-mediated hemolytic transfusion reactions usually result in extravascular hemolysis. Rh antibodies are IgG and can cross the placenta to coat fetal (Rh-positive) RBCs.

5. How are Rh antigens inherited? a. b. c. d.

Autosomal recessive alleles Sex-linked genes Codominant alleles X-linked

6. Biochemically speaking, what type of molecules are Rh

antigens? a. Glycophorins b. Simple sugars c. Proteins d. Lipids 7. Rh antibodies react best at what temperature (°C)? a. b. c. d.

22 18 15 37

8. Rh antibodies are primarily of which immunoglobulin

class? a. IgA b. IgM c. IgG d. IgD

2682_Ch07_149-171 22/05/12 11:43 AM Page 170

170

PART II

Blood Groups and Serologic Testing

9. Rh antibodies have been associated with which of the

following clinical conditions? a. Erythroblastosis fetalis b. Thrombocytopenia c. Hemophilia A d. Stomatocytosis 10. What do Rhnull cells lack? a. b. c. d.

Lewis antigens Normal oxygen-carrying capacity Rh antigens MNSs antigens

11. What antigen system is closely associated phenotypically

with Rh? a. McCoy b. Lutheran c. Duffy d. LW 12. Anti-LW will not react with which of the following? a. b. c. d.

Rh-positive RBCs Rh-negative RBCs Rhnull RBCs Rh:33 RBCs

13. Convert the following genotypes from Wiener nomen-

clature to Fisher-Race and Rosenfield nomenclatures, and list the antigens present in each haplotype. a. R1r b. R2R0 c. RzR1 d. ryr 14. Which Rh phenotype has the strongest expression of D? a. b. c. d.

R1r R1R1 R2R2 D–

15. Which of the following most commonly causes an

individual to type RhD positive yet possess anti-D? a. Genetic weak D b. Partial D c. C in trans to RHD d. D epitopes on RhCE protein 16. An individual has the following Rh phenotype:

D+C+E+c+e+. Using Fisher-Race terminology, what is their most likely Rh genotype? a. DCE/Dce b. DCE/dce c. DCe/dcE d. DCe/DcE 17. Which of the following is the most common Rh pheno-

type in African Americans? a. Dce/dce b. DcE/dce c. DCe/dce d. Dce/dCe

References 1. Levine, P, and Stetson, RE: An unusual case of intragroup agglutination. JAMA 113:126, 1939. 2. Landsteiner, K, and Wiener, AS: An agglutinable factor in human blood recognized by immune sera for rhesus blood. Proc Soc Exp Biol (NY) 43:223, 1940. 3. Levine, P, et al: The role of isoimmunization in the pathogenesis of erythroblastosis fetalis. Am J Obstet Gynecol 42:925, 1941. 4. Race, RR, et al: Recognition of a further common Rh genotype in man. Nature 153:52, 1944. 5. Mourant, AE: A new rhesus antibody. Nature 155:542, 1945. 6. Stratton, F: A new Rh allelomorph. Nature 158:25, 1946. 7. Levine, P: On Hr factor and Rh genetic theory. Science 102:1, 1945. 8. Race, RR: The Rh genotypes and Fisher’s theory. Blood 3 (Suppl 2):27, 1948. 9. Wiener, AS: Genetic theory of the Rh blood types. Proc Soc Exp Biol (NY) 54:316, 1943. 10. Rosenfield, RE, et al: A review of Rh serology and presentation of a new terminology. Transfusion 2:287, 1962. 11. Lewis, M: Blood group terminology 1990. Vox Sang 58:152, 1990. 12. Tippett, PA: A speculative model for the Rh blood groups. Ann Hum Genet 50:241, 1986. 13. Cherif-Zahar, B, Bloy, C, Le Van Kim, C, et al: Molecular cloning and protein structure of a human blood group Rh polypeptide. Proc Natl Acad Sci USA Aug;87(16):6243–6247, 1990. 14. Le van Kim, C, Mouro, I, Cherif-Zahar, B, et al: Molecular cloning and primary structure of human blood group RhD polypeptide. Proc Natl Acad Sci USA Nov 15;89(22):10925– 10929,1992. 15. Arce, MA, Thompson, ES, Wagner, S, et al: Molecular cloning of RhD cDNA derived from a gene present in RhD-positive, but not RhD-negative individuals. Blood Jul 15;82(2):651–655, 1993. 16. Ridgewell, K, Spurr, NK, Laguda, B, et al: Isolation of cDNA clones for a 50 kDa glycoprotein of the human erythrocyte membrane associated with Rh (rhesus) blood group antigen expression. Biochem J 287:223–228, 1992. 17. Colin, Y, Cherif-Zahar, B, Le Van Kim, C, et al: Genetic basis of the RhD-positive and RhD-negative blood group polymorphism as determined by Southern analysis. Blood 78:2747– 2752, 1991. 18. Singleton, BK, Green, CA, Avent, ND, et al: The presence of an RHD pseudogene containing a 37 base pair duplication and nonsense mutation in Africans with the RhD-negative blood group phenotype. Blood 95(1):12–18, 2000. 19. Shao, CP, Maas, JH, Su, YQ, et al: Molecular background of Rh D-positive, D-negative, D (el) and weak D phenotypes in Chinese. Vox Sang 83:156–161, 2002. 20. Blumenfeld, OO, and Patnaik, SK: Allelic genes of blood group antigens: A source of human mutations and cSNPs documented in the Blood Group Antigen Gene Mutation Database. Hum Mutat Jan;23(1):8–16, 2004. 21. Avent, ND, Butcher, SK, Liu, W et al: Localization of the C termini of the Rh (rhesus) polypeptides to the cytoplasmic face of the human erythrocyte membrane. J Biol Chem 267:15134– 15139, 1992. 22. Avent, ND, Liu, W, Warner, KM, et al: Immunochemical analysis of the human erythrocyte Rh polypeptides. J Biol Chem 271:14233–14239, 1996. 23. Hughes-Jones, NC, Gardner, B, and Lincoln, PJ: Observations of the number of available c, D, and E antigen sites on red cells. Vox Sang 21:210, 1971. 24. Westhoff, CM, and Wylie, DE: Transport characteristics of mammalian Rh and Rh glycoproteins expressed in heterologous systems. Transfus Clin Biol 13:132–138, 2006.

2682_Ch07_149-171 22/05/12 11:43 AM Page 171

Chapter 7 The Rh Blood Group System 25. Roback, JD, Combs, MR, Grossman, B, and Hillyer, C (eds): Technical Manual, 16th ed. AABB, Bethesda, MD, 2008. 26. Race, RR, Sanger, R, and Lawler, SD: The Rh antigen Du. Ann Eugen Lond 14:171, 1948. 27. Westhoff, CM: Rh complexities: Serology and DNA typing. Transfusion 47:17S–22S, 2007. 28. Beckers, EA, Faas, BH, von dem Borne, AE, et al: The R0Har RH:33 phenotype results from substitution of exon 5 of the RHCE gene by the corresponding exon of the RHD gene. Br J Haematol Mar 92(3):751–757, 1996. 29. Flegel, WA, Wagner, FF, Chen, Q, et al: The RHCE allele ceCF: The molecular basis of Crawford (RH43). Transfusion 46(8):1334–1342, 2006. 30. Ceppellini, R, Dunn, LC, and Turri, M: An interaction between alleles at the Rh locus in man which weakens the reactivity of the Rh0 factor (D0). Proc Natl Acad Sci 41:283, 1955. 31. Wagner, FF, Gassner, C, Muller, TH, et al: Molecular basis of weak D phenotypes. Blood 93:385–393, 1999. 32. Tippett, P, Lomas-Francis, C, and Wallace, M: The Rh antigen D: Partial D antigens and associated low incidence antigens. Vox Sang 70:123–131, 1996. 33. Shapiro, M: The ABO, MN, P and Rh blood group systems in South African Bantu: A genetic study. South Afr Med J 25:187, 1951. 34. Argall, CI, Ball, JM, and Trentelman, E: Presence of anti-D antibody in the serum of Du patient. J Clin Lab Med 41:895, 1953. 35. Wiener, AS, and Unger, LJ: Rh factors related to the Rh0 factor as a source of clinical problems. JAMA 169:696, 1959. 36. Tippett, P, and Sanger, R: Observations on subdivisions of the Rh antigen D. Vox Sang 7:9, 1962. 37. Huang, CH, Liu, P, and Cheng, JG: Molecular biology and genetics of the Rh blood group system. Semin Hematol 37:150– 165, 2000. 38. Tippett, P, Lomas-Francis, C, and Wallace, M. The Rh antigen D: Partial D antigens and associated low incidence antigens. Vox Sang 70:123–131, 1996. 39. Mollison, PL: Blood Transfusion in Clinical Medicine, 6th ed. Blackwell Scientific Publications, Oxford, 1988. 40. Diamond, LK, and Denton, RC: Rh agglutination in various media with particular reference to the value of albumin. J Clin Lab Med 30:821, 1945. 41. Romans, DG, et al: Conversion of incomplete antibodies to direct agglutinins by mild reduction. Proc Natl Acad Sci USA 74:2531, 1977. 42. Denomme, GA, Dake, LR, Vilensky, D, Ramyar, L, and Judd, WJ: Rh discrepancies caused by variable reactivity of partial and weak D types with different serologic techniques. Transfusion 48(3):473–478, 2008. 43. Queenan, JT: Modern Management of the Rh Problem, 2nd ed. Harper & Row, New York, 1977. 44. Schmidt, PJ, et al: Aberrant U blood group accompany Rhnull. Transfusion 7:33, 1967. 45. Schmidt, PJ, and Vos, GH: Multiple phenotypic abnormalities associated with Rhnull (—/—). Vox Sang 13:18, 1967. 46. Chown, B, et al: An unlinked modifier of Rh blood groups: Effects when heterozygous and when homozygous. Am J Hum Genet 24:623, 1972.

171

47. Daniels, G: Human Blood Groups, 2nd ed. Blackwell Scientific, Oxford, 2002. 48. Reid, MR, and Lomas-Francis, C. The Blood Group Antigen Facts Book, 2nd ed. Elsevier, San Diego, 2004. 49. Issitt, PD, and Anstee, DJ: Applied Blood Group Serology, 4th ed. Montgomery Scientific Publications, Durham, NC, 1998. 50. Callendar, ST, and Race, RR: A serological and genetic study of multiple antibodies formed in response to blood transfusion by a patient with lupus erythematosus diffuses. Ann Eugen Lond 13:102, 1946. 51. Sistonen, P, et al: MAR, a novel high-incidence Rh antigen revealing the existence of an allele sub-system including Cw (Rh8) and Cx (Rh9) with exceptional distribution in the Finnish population. Vox Sang 66:287–292, 1994. 52. Rosenfield, RE, and Haber, GV: An Rh blood factor, Rh1 (Ce) and its relationship to hr (ce). Am J Hum Genet 10:474, 1958. 53. Chen, YX, Peng, J, Novaretti, M, Reid, ME, and Huang, CH: Deletion of arginine codon 229 in the Rhce gene alters e and f but not c antigen expression. Transfusion Mar;44(3):391–398, 2004. 54. Allen, FH, and Tippett, PA: A new Rh blood type which reveals the Rh antigen G. Vox Sang 3:321, 1958. 55. Wiener, AS, and Unger, LJ: Further observations on the blood factors RhA, RhB, RhC, RhD. Transfusion 2:230, 1962. 56. Allen, FH, Jr, and Corcoran, PA: Proc 11th Ann Mtg. AABB, Cincinnati, Abstract, 1958. 57. Chown, B, et al: The Rh antigen Dw (Wiel). Transfusion 4:169, 1964. 58. Lewis, M, et al: Blood group antigen Goa and the Rh system. Transfusion 7:440, 1967. 59. Lewis, M, et al: Assignment of the red cell antigen Targett (Rh 40) to the Rh blood group systems. Am J Hum Genet 31:630, 1979. 60. Giles, CM, et al: An Rh gene complex which results in a “new” antigen detectable by a specific antibody, anti-Rh 33. Vox Sang 21:289, 1971. 61. Rosenfield, RE, et al: Problems in Rh typing as revealed by a single Negro family. Am J Hum Genet 12:147, 1960. 62. Issitt, PD: Applied Blood Group Serology, 3rd ed. Montgomery Scientific Publication, Miami, FL, 1985. 63. Vege, S, and Westhoff, CM. Molecular characterization of GYPB and RH in donors in the American Rare Donor Program. Immunohematology 22:143–147, 2006. 64. Huang, CH, Chen, Y, and Reid, M: Human D(IIIa) erythrocytes: RhD protein is associated with multiple dispersed amino acid variations. Am J Hematol. Jul;55(3):139–145, 1997. 65. DeNatale, A, et al: A “new” Rh antigen, common in Negroes, rare in white people. JAMA 159:247, 1955. 66. Sanger, R, et al: An Rh antibody specific for V and Rs. Nature (Lond) 186:171, 1960. 67. Daniels, GL, Faas, BH, Green, CA, et al: The VS and V blood group polymorphisms in Africans: A serologic and molecular analysis. Transfusion 38:951–958, 1998. 68. Contreras, M, et al: The Rh antigen Evans. Vox Sang 34:208, 1978. 69. Race, RR, and Sanger, R: Blood Groups in Man, 6th ed. Blackwell Scientific, Oxford, 1975.

2682_Ch08_172-215 22/05/12 11:44 AM Page 172

Chapter

8

Blood Group Terminology and the Other Blood Groups Regina M. Leger, MSQA, MT(ASCP)SBB, CMQ/OE(ASQ)

Introduction Blood Groups and Terminology The Lewis (007) System Lewis Antibodies Genetics and Biosynthesis Development of Lewis Antigens Other Lewis Antigens The P Blood Group: P1PK (003) and Globoside (028) Systems and Related (209) Antigens The P1 Antigen Anti-P1 Biochemistry Genetics Other Sources of P1 Antigen and Antibody Anti-PP1Pk Alloanti-P Autoanti-P Associated With Paroxysmal Cold Hemoglobinuria Antibodies to Compound Antigens Luke (LKE) Antigen Disease Associations The I (027) System and i Antigen The I and i Antigens Anti-I Anti-i Biochemistry and Genetics Other Sources of I and i Antigen The IT Antigen and Antibody Antibodies to Compound Antigens Disease Associations The MNS (002) System M and N Antigens S and s Antigens Anti-M Anti-N Anti-S and Anti-s Biochemistry Genetics

172

GPA- and GPB-Deficient Phenotypes Other Antibodies in the MNS System Autoantibodies Disease Associations The Kell (006) and Kx (019) Systems K and k Antigens Kpa, Kpb, and Kpc Antigens Jsa and Jsb Antigens Anti-K Antibodies to Kpa, Jsa, and Other Low-Prevalence Kell Antigens Antibodies to k, Kpb, Jsb, and Other High-Prevalence Kell Antigens Biochemistry Genetics The Kx Antigen The Ko Phenotype and Anti-Ku(K5) The McLeod Phenotype and Syndrome Altered Expressions of Kell Antigens Autoantibodies The Duffy (008) System Fya and Fyb Antigens Anti-Fya and Anti-Fyb Biochemistry Genetics Fyx Fy3 Antigen and Antibody Fy5 Antigen and Antibody The Kidd (009) System Jka and Jkb Antigens Anti-Jka and Anti-Jkb Biochemistry Genetics Jk(a–b–) Phenotype and the Recessive Allele, Jk Jk(a–b–) Phenotype and the Dominant In(Jk) Allele Anti-Jk3 Autoantibodies

The Lutheran (005) System Lua and Lub Antigens Anti-Lua Anti-Lub Biochemistry Genetics Lu(a–b–) Phenotypes Anti-Lu3 The Diego (010) System The Yt (011) System The Xg (012) System The Scianna (013) System The Dombrock (014) System The Colton (015) System The Landsteiner-Wiener (016) System The Chido/Rodgers (017) System The Gerbich (020) System The Cromer (021) System The Knops (022) System The Indian (023) System The Ok (024) System The Raph (025) System The John Milton Hagen (026) System The Gill (029) System The Rh-associated Glycoprotein (030) System Miscellaneous Antigens Vel Ata Jra Sda Applications to Routine Blood Banking Summary Chart Review Questions References

2682_Ch08_172-215 22/05/12 11:44 AM Page 173

Chapter 8 Blood Group Terminology and the Other Blood Groups

173

OBJECTIVES Blood Group Terminology 1. Describe how antigens, antibodies, genes, and phenotypes are correctly written. 2. List the four categories for classification of RBC surface blood group antigens used by the ISBT. 3. For each of the blood group systems described in this chapter: • List the major antigens and common phenotypes • Describe the serologic characteristics and clinical significance of the antibodies • Identify null phenotypes

Antigen Characteristics 4. Describe the formation of Lewis antigens and their adsorption onto RBCs. 5. Define the interaction of Lewis genes with ABO, H, and secretor genes. 6. List substances present in secretions and the Lewis phenotypes based on a given genotype. 7. Describe the reciprocal relationship of I antigen to i antigen. 8. List the antigen frequencies for the common antigens K, M, S, s, Fya, Fyb, Jka, Jkb, and P1. 9. Define Kpa, Jsa, and Lua as low-prevalence antigens and Kpb, Jsb, Lub, and I as high-prevalence antigens. 10. Define the association of M and N with glycophorin A (GPA) and S and s with glycophorin B (GPB). 11. Describe the antigen phenotypes S–s–U–, Js(a+), and Fy(a–b–) associated with blacks. 12. Define the null phenotypes Mk, p, Ko, Fy(a–b–), Jk(a–b–), and Lu(a–b–), and describe their role in problem-solving. 13. Compare dominant and recessive forms of the Lu(a–b–) and Jk(a–b–) phenotypes. 14. Explain I, P1, and Lutheran antigens as being poorly expressed on cord RBCs. 15. Describe the phenotypic relationship between LW and Rh. 16. List the Gerbich-negative phenotypes and the antibodies that can be made by each. 17. List the antigens that are denatured by routine blood bank enzymes (M, N, S, s, Fya, Fyb) and antigens whose reactivity with antibody is enhanced with enzymes (I, i, P1, Jka, Jkb). 18. List which antigens are destroyed by treatment with DTT (dithiothreitol). 19. Explain the prevalence of Dia with South, Central, and North American native populations, and the consequent higher prevalence of the Di(b–) phenotype in those populations.

Antibody Characteristics 20. List the characteristics of the Lewis antibodies, including clinical significance. 21. Define antibodies to M, N, I, and P1 as being typically non-RBC-induced (“naturally occurring”), cold-reacting agglutinins that are usually clinically insignificant. 22. Describe antibodies to K, k, S, s, Fya, Fyb, Jka, and Jkb as usually induced by exposure to foreign RBCs (“immune”), antiglobulinreactive antibodies that are clinically significant. 23. List the antibody specificities that commonly show dosage (anti-M, -N, -S, -s, -Fya, -Fyb, -Jka and -Jkb). 24. Describe the characteristic reactivity of antibodies to Ch, Rg, JMH, and Knops antigens, and their clinical significance. 25. List the antibodies in the Dombrock system that are clinically significant for transfusion (anti-Doa and anti-Dob).

Clinical Significance and Disease Association 26. List and correlate the common 37°C antihuman globulin–reactive antibodies K, k, S, s, Fya, Fyb, Jka, and Jkb with hemolytic transfusion reactions (HTR) and hemolytic disease of the fetus and newborn (HDFN). 27. Describe why the Kidd antibodies are a common cause of delayed HTR. 28. Define the relationship of autoanti-I with Mycoplasma pneumoniae infections and autoanti-i with infectious mononucleosis. 29. Describe the common characteristics of the McLeod syndrome, including very weak Kell antigen expression, acanthocytosis, and late onset of muscular and neurological abnormalities. 30. Describe the association of the Fy(a–b–) phenotype with Plasmodium vivax resistance. 31. Explain Jk(a–b–) RBCs with a resistance to lysis that normally occurs in 2M urea, a common diluting fluid used for automated platelet counters.

2682_Ch08_172-215 22/05/12 11:44 AM Page 174

174

PART II

Blood Groups and Serologic Testing

Introduction The first part of this chapter covers blood group terminology and how antigens are organized into a classification scheme. Conventions for the correct use of terminology are included so that the student will be able to accurately communicate information about antigens and antibodies, phenotypes, and genotypes. The ABO and Rh blood groups are the most significant in transfusion practice. However, there are over 300 RBC antigens that are formally recognized internationally. Blood group antigens are defined by carbohydrates (sugars) attached to glycoprotein or glycolipid structures or by amino acids on a protein. The carbohydrate blood groups Lewis, P, and I will be presented first. The antigens of these carbohydrate systems (like ABO and H) are not encoded by their genes directly. Rather, the genes encode specific glycosyltransferases that in turn synthesize the carbohydrate epitopes by sequential addition of sugars to a precursor. The next blood groups discussed are MNS, Duffy, Kell, and Kidd. These are significant in routine transfusion medicine; antibodies to these antigens are more commonly encountered. The chapter then addresses the remainder of the blood groups and selected antigens. Antibodies to these latter will be rarely encountered, but it is important for clinical laboratorians to know that these other antigens and corresponding antibodies exist. While there is more information presented here than is required to work capably at the bench, students will be better prepared for those real-life situations when they encounter one of these uncommon antibodies. Antigen and antibody characteristics are discussed for each blood group presented. Included are the effects of enzymes and chemical treatments on test RBCs. This information is a tool for antibody identification. For example, if an antibody no longer reacts with a panel of RBCs after the RBCs have been pretreated with an enzyme such as ficin or papain, then only those antibodies that don’t react after enzyme treatment are considered for the specificity, and all other specificities can be excluded. These antigen and antibody characteristics are summarized on the front and back cover of the book so that students can easily access pertinent information while performing routine antibody identification.

Blood Groups and Terminology A blood group system is one or more antigens produced by alleles at a single gene locus or at loci so closely linked that crossing over does not occur or is very rare.1 With a few notable exceptions, most blood group genes are located on the autosomal chromosomes and demonstrate straightforward Mendelian inheritance. Most blood group alleles are codominant and express a corresponding antigen. For example, a person who inherits alleles K and k expresses both K and k antigens on his or her RBCs. Some genes code for complex structures that carry more than one antigen (e.g., the glycophorin B structure, which carries S or s antigen, also carries the U antigen).

Silent, or amorphic, alleles exist that make no antigen, but they are rare. When paired chromosomes carry the same silent allele, a null phenotype results. Null phenotype RBCs can be very helpful when evaluating antibodies to unknown high-prevalence antigens. For example, an antibody reacting with all test cells except those with the phenotype Lu(a–b–) may be directed against an antigen in the Lutheran system or an antigen phenotypically related to the Lutheran system. In some blood group systems, the null phenotype results in RBC abnormalities. Some blood group systems have regulator or modifying genes, which alter antigen expression. These are not necessarily located at the same locus as the blood group genes they affect and may segregate independently. For example, RBCs with the dominant type of Lu(a–b–) have suppressed expression of all the antigens in the Lutheran blood group system as well as many other antigens, including P1 and i. This modifying gene is inherited independently of the genes coding for Lutheran, P1, and i antigens. Blood group antigens are detected by alloantibodies, which occur naturally (i.e., without a known immune stimulus) or as a response by the immune system after exposure to non-self RBC antigens introduced by blood transfusion or pregnancy. Over the last century, blood group antigens have been named using several styles of symbols: uppercase single letters, uppercase and lowercase letters to represent alleles, letters derived from the name of the system (some with superscripts to represent alleles), letter symbols followed by numbers, and finally the more recent use of all uppercase letters. Although gene and antigen names seem confusing at first, certain conventions are followed when writing alleles, antigens, and phenotypes.1 Some examples are given in Table 8–1. Genes are written in italics or underlined when italics are not available (e.g., when handwritten), and their allele number or letter is always superscript. Antigen names are written in regular type without italics or underlining; some antigens have numbers or superscript letters. A phenotype is a description of which antigens are present on an individual’s RBCs and simply indicates the results of serologic tests on those RBCs. It is important to use subscripts, superscripts, and italics appropriately. For example, A1, A1 and A1 mean the antigen, the phenotype, and the allele respectively. How the phenotype is written depends on the antigen nomenclature and whether letters or numbers are used. For letter antigens, a plus sign or minus sign written on the same line as the antigen is used to designate that the antigen is present or absent, respectively. Examples are M+ and K–. For antigens that have superscripts, the letter of the superscript is placed in parentheses on the same line as the letter defining the antigen—for example, Fy(a+) and Jk(a–). When testing for both of the antithetical antigens, both results are written within the parentheses—for instance, Fy(a–b+). For antigens that have a numerical designation, the letter(s) defining the system is followed by a colon, followed by the number representing the antigen. No plus sign is written if the antigen is present, but a minus sign is placed before the

2682_Ch08_172-215 22/05/12 11:44 AM Page 175

Chapter 8 Blood Group Terminology and the Other Blood Groups

175

Table 8–1 Examples of Terminology for Genes, Antigens, Antibodies, and Phenotypes GENE

ANTIGEN

System

Conventional

ISBT

Lewis

Le le

LE

Lea Leb

MNS

M N S s

MNS*1 MNS*2 MNS*3 MNS*4

Kell

K k

Kidd

Jka Jkb

ANTIBODY

PHENOTYPE Antigen Positive

Antigen Negative

Anti-Lea Anti-Leb

Le(a+) Le(b+)

Le(a–) Le(b–)

M N S s

Anti-M Anti-N Anti-S Anti-s

M+ N+ S+ s+

M– N– S– s–

KEL*1 KEL*2

K k

Anti-K Anti-k

K+ k+

K– k–

JK*1 JK*2

Jka Jkb

Anti-Jka Anti-Jkb

Jk(a+) Jk(b+)

Jk(a–) Jk(b–)

negative result, and multiple results are separated by a comma (e.g., Sc:–1,2). Phenotypes of more than one blood group system are separated by a semicolon—for example, S+s+; K–; Fy(a+b–). One must remember that serologic tests determine only RBC phenotype, not genotype. A genotype is composed of the actual genes that an individual has inherited and can be determined only by family or DNA studies. Sometimes the genotype can be predicted or inferred by the phenotype. When based on results from RBC antigen typing, the genotype is a probable interpretation as to which genes the individual carries in order to have the observed phenotype. Antibodies are described by their antigen notation with the prefix anti-, including a hyphen before the antigen symbol. Use of correct blood group terminology, especially for antibodies identified in a patient’s serum, is very important so that correct information is conveyed for patient care. Some examples of correct and incorrect terminology are given in Table 8–2. Numeric terminology was originally introduced for the Kell and Rh systems and was subsequently applied to other systems. To facilitate computer storage and retrieval of blood group information and to help standardize blood group system and antigen names, the International Society of Blood

Table 8–2 Examples of Correct and Incorrect Terminology CORRECT

INCORRECT

Fy(a+)

Fya+, Fy(a+), Fya+, Fya(+), Duffy a-positive, Duffya+

Fy(a–b+)

Fya–b+, Fya(–)Fyb(+)

Anti-Fya

Anti Fya, anti-Duffy, anti-Duffya

K

Kell (name of system), K1

Anti-k

Anti-Cellano, anti-K2

M+N–

M(+), MM

Ge:–2

Ge2–, Ge:2–, Ge2-negative

Transfusion (ISBT) formed the Working Party on Terminology for Red Cell Surface Antigens in 1980.2 The numeric system this group proposed was not intended to replace traditional terminology but rather to enable communication on computer systems where numbers are necessary. Each antigen is given a six-digit identification number. The first three digits represent the system, collection, or series, and the second three digits identify the antigen. The antigens within the system are numbered sequentially in order of discovery. Each system also has an alphabetical symbol. For example, using the ISBT terminology, the K antigen is 006001 with the first three numbers (006) representing the system and the second three numbers (001) representing the number assigned to K. Antigens can also be written using the system symbol followed by the antigen number; for instance, KEL1 (the redundant sinistral zeroes can be omitted). This committee’s work is ongoing, and the assignment of RBC antigens to blood group systems is periodically updated. The first monograph was released in 1990, and updates are published in Vox Sanguinis3 and on the Working Party’s page of the ISBT website (www.isbtweb.org). The ISBT assigns RBC antigens to a system, collection, or low- or high-prevalence series. This chapter uses traditional terminology, but the ISBT symbol and number are indicated for the blood group systems and collections discussed. As defined by the ISBT, a blood group system “consists of one or more antigens controlled at a single gene locus, or by two or more very closely linked homologous genes with little or no observable recombination between them.”4 Each system is genetically distinct. To date, there are 30 blood group systems (Table 8–3).3 Collections are antigens that have a biochemical, serologic, or genetic relationship but do not meet the criteria for a system.4 Antigens classified as a collection are assigned a 200 number. Some of the previously established collections have been made obsolete as criteria have been met to establish a system or incorporate antigens into an existing system. See Table 8–4 for a listing of the ISBT collections. All remaining RBC antigens that are not associated with a system or a collection are catalogued into the 700 series of

2682_Ch08_172-215 22/05/12 11:44 AM Page 176

176

PART II

Blood Groups and Serologic Testing

Table 8–3 International Society of Blood Transfusion (ISBT) Blood Group Systems NUMBER

NAME

SYMBOL

GENE NAME ISBT (HGNC)

CHROMOSOMAL LOCATION

NO. OF AGS

001

ABO

ABO

ABO (ABO)

9q

4

002

MNS

MNS

MNS (GYPA, GYPB, GYPE)

4q

46

003

P1PK

P1PK

P1PK (A4GALT)

22q

2

004

Rh

RH

RH (RHD, RHCE)

1p

52

005

Lutheran

LU

LU (LU)

19q

20

006

Kell

KEL

KEL (KEL)

7q

32

007

Lewis

LE

LE (FUT3)

19p

6

008

Duffy

FY

FY (DARC)

1q

5

009

Kidd

JK

JK (SLC14A1)

18q

3

010

Diego

DI

DI (SLC4A1)

17q

22

011

Yt

YT

YT (ACHE)

7q

2

012

Xg

XG

XG (XG) MIC2 (CD99)

X

2

013

Scianna

SC

SC(ERMAP)

1p

7

014

Dombrock

DO

DO (ART4)

12p

7

015

Colton

CO

CO (AQP1)

7p

4

016

LandsteinerWiener

LW

LW (ICAM4)

19p

3

017

Chido/Rodgers

CH/RG

CH/RG (C4A, C4B)

6p

9

018

H

H

H (FUT1)

19q

1

019

Kx

XK

XK (XK)

Xp

1

020

Gerbich

GE

GE (GYPC)

2q

11

021

Cromer

CROM

CROM (CD55)

1q

16

022

Knops

KN

KN (CR1)

1q

9

023

Indian

IN

IN (CD44)

11p

4

024

Ok

OK

OK (BSG)

19p

3

025

Raph

RAPH

RAPH (CD151)

11p

1

026

John Milton Hagen

JMH

JMH (SEMA7A)

15q

6

027

I

I

IGNT (GCNT2)

6p

1

028

Globoside

GLOB

GLOB (B3GALT3)

3q

1

029

Gill

GIL

GIL (AQP3)

9p

1

030

Rh-associated glycoprotein

RHAG

RHAG (RHAG)

6p

2

HGNC = Human Gene Nomenclature Committee

2682_Ch08_172-215 22/05/12 11:44 AM Page 177

Chapter 8 Blood Group Terminology and the Other Blood Groups

Table 8–4 International Society of Blood Transfusion Blood Group Collections COLLECTION

ANTIGEN

Number

Name

Symbol

205

Cost

COST

205001 205002

Csa Csb

207

Ii

I

207002

i

208

Er

ER

208001 208002 208003

Era Erb Er3

209003 209004

LKE PX2

210001 210002

Lec Led

VEL

212001 212002

Vel ABTI

MN CHO

213001 213002 213003 213004 213005 213006

Hu M1 Tm Can Sext Sj

209

Number

GLOB

210 212

Vel

213

Symbol

177

low-prevalence antigens or the 901 series of high-prevalence antigens. Refer to Table 8–5 for a listing of low- and highprevalence antigens recognized by the ISBT. Antigens in these series represent those with a prevalence of less than 1% or more than 90% of most random populations, respectively. As terminology has evolved, the terms high- and low-incidence, also previously known as high- and lowfrequency, are currently being replaced by the terms high- and low-prevalence, reflecting the occurrence of an inherited characteristic at the phenotypic level.5

The Lewis (007) System

Antigens in shaded boxes are discussed in text.

The Lewis blood group system is unique because the Lewis antigens are not intrinsic to RBCs but are on type 1 glycosphingolipids that are passively adsorbed onto the RBC membrane from the plasma. The Lewis system was named after one of the first individuals to make the antibody, reported by Mourant in 1946.6 This antibody, later called anti-Lea, agglutinated RBCs from about 25% of English people.7 In 1948, an antibody, later called anti-Leb, was found that reacted with Le(a–) individuals. It was thought that Lea and Leb were antithetical antigens, but we now know this is not so because they do not result from alternative alleles of a single gene. Rather, they result from the interaction of two fucosyltransferases encoded by independent genes, Le and Se. The Lewis blood group system has been assigned the ISBT system number 007 and the system symbol LE.

Table 8–5 International Society of Blood Transfusion Antigens of Low (700 Series) and High (901 Series) Prevalence NUMBER Lows

Highs

NAME

SYMBOL

700002

Batty

By

700039

Milne

700003

Christiansen

Chra

700040

Rasmussen

700005

Biles

Bi

700044

700006

Box

Bxa

700045

Katagiri

Kg

700017

Torkildsen

Toa

700047

Jones

JONES

700018

Peters

Pta

700049

HJK

700019

Reid

Rea

700050

HOFM

700021

Jensen

Jea

700052

SARA

700028

Livesay

Lia

700054

REIT

901002

Langereis

Lan

901009

Anton

AnWj

901003

August

Ata

901012

Sid

Sda

901005

Jra

901014

PEL

901008

Emm

901016

MAM

Antigens in shaded boxes are discussed in text.

NUMBER

NAME

SYMBOL

RASM JFV

2682_Ch08_172-215 22/05/12 11:44 AM Page 178

178

PART II

Blood Groups and Serologic Testing

Basic Concepts There are several Lewis antigens, but the two of primary concern are Lea and Leb. The Lewis (Le, FUT3) gene is located on chromosome 19 (at 19p13.3), as is the secretor (Se, FUT2) gene at 19q13.3. There are two alleles at the Lewis locus, Le and the amorph le, and there are two alleles at the secretor locus, Se and the amorph se. The biochemistry and interaction of the genes at these two loci will be explained in a later section, but in short, the Le gene must be present for a precursor substance to be converted to Lea, but the Se gene must also be present for conversion to Leb. The four phenotypes resulting from the interaction of these two genes are shown in Table 8–6. In 1948, it was observed that individuals with Le(a+) RBCs were mostly nonsecretors of ABH.8 As a result, in general for adults, Le(a+b–) RBCs are from ABH nonsecretors and Le(a–b+) RBCs are from ABH secretors (refer to Chapter 6, “The ABO Blood Group System”). Individuals with the Le(a–b–) RBC phenotype are either secretors or nonsecretors.7 The Le(a–b–) phenotype is found more frequently among Africans. The Le(a+b+) phenotype is rare among whites and Africans but is more frequent among Asians, with a prevalence of 10% to 40%.9 The antigens of the Lewis blood group system recognized by the ISBT are listed in Table 8–7. Lewis antigens are not expressed on cord RBCs and are often diminished on the mother’s RBCs during pregnancy. Lewis antigens are found on lymphocytes and platelets and on other tissues such as the pancreas, stomach, intestine, skeletal muscle, renal cortex, and adrenal glands.9 In addition, soluble Lewis antigens are found in saliva as glycoproteins. Lewis antigens are resistant to treatment with the enzymes ficin and papain, dithiothreitol (DTT), and glycine-acid EDTA. Reactivity of Lewis antibodies can be greatly enhanced by testing with enzyme-treated RBCs; hemolysis of enzymetreated RBCs may be seen if serum is tested.

Lewis Antibodies Lewis antibodies are often naturally occurring and made by Le(a–b–) persons; that is, they occur without any known

Table 8–6 Phenotypes of the Lewis System ADULT PHENOTYPE PREVALENCE (%)

PHENOTYPE

Whites

Blacks

Le(a+b–)

22

23

Le(a–b+)

72

55

Le(a–b–)

6

22

Le(a+b+)

Rare

Rare

Table 8–7 Antigens of the Lewis Blood Group System ANTIGEN

ISBT NUMBER

Lea

LE1

Leb

LE2

Leab

LE3

Anti-Leab reacts with Le(a+b–) and Le(a–b+) RBCs from adults and with 90% cord RBCs.*

LebH

LE4

Anti-LebH reacts with group O Le(b+) and A2 Le(b+) RBCs.

ALeb

LE5

Anti-Aleb reacts with group A1 Le(b+) and A1B Le(b+) RBCs.

BLeb

LE6

Anti-BLeb reacts with group B Le(b+) and A1B Le(b+) RBCs.

COMMENT

*Reactive cord RBCs [serologically Le(a–b–)] are from babies with Le gene.

RBC stimulus. They are generally IgM and do not cross the placenta. Because of this and because the Lewis antigens are not well developed on fetal RBCs, the antibodies do not cause hemolytic disease of the fetus and newborn (HDFN). Anti-Lea and anti-Leb may occur together and can be neutralized by the Lewis substances present in plasma or saliva or with commercially prepared Lewis substance. Lewis antibodies occur quite frequently in the sera of pregnant women who transiently exhibit the Le(a–b–) phenotype. Most Lewis antibodies agglutinate saline suspended RBCs, but these agglutinates are often fragile and can be easily dispersed if the cell button is not gently resuspended after centrifugation. Lewis antibodies can bind complement, and when fresh serum is tested, anti-Lea may cause in vitro hemolysis of incompatible RBCs, though this is more often seen with enzyme-treated RBCs than with untreated RBCs. Anti-Lea is the most commonly encountered of the Lewis antibodies and is often detected in room temperature tests, but it sometimes reacts at 37°C and in the indirect antiglobulin test. Rare hemolytic transfusion reactions (HTR) have been reported in patients with anti-Lea who were transfused with Le(a+) RBCs, so anti-Lea that are reactive at 37°C, particularly those that cause in vitro hemolysis, should not be ignored.1 It is relatively easy to find Le(a–) units since 80% of the population are secretors. Obtaining donor units that are typed Le(a–) with reagent antisera is generally not considered necessary for these patients; units that are crossmatch compatible in tests performed at 37°C are acceptable. Persons whose RBCs are Le(a–b+) do not make anti-Lea, because small amounts of unconverted Lea are present in their plasma and saliva. Anti-Leb is not as common or generally as strong as anti-Lea. It is usually an IgM agglutinin and can bind complement. AntiLeb is infrequently made by Le(a+b–) individuals and can be classified into two categories: anti-LebH and anti-LebL. Anti-LebH reacts best when both the Leb and the H antigens are present on the RBC, such as group O and A2 cells. Anti-LebH represents

2682_Ch08_172-215 22/05/12 11:44 AM Page 179

Chapter 8 Blood Group Terminology and the Other Blood Groups

an antibody to a compound antigen. Anti-LebL recognizes any Leb antigen regardless of the ABO type. Anti-LebH should be suspected when anti-Leb is identified with a panel of RBCs (group O) but most or all group A donor units are crossmatch compatible (as only about 20% of the group A RBC units will be from group A2 individuals). Lewis antigens are not intrinsic to the RBC membrane and are readily shed from transfused RBCs within a few days of transfusion. Also, Lewis blood group substance present in transfused plasma neutralizes Lewis antibodies in the recipient.5 This is why it is exceedingly rare for anti-Lea or anti-Leb to cause hemolysis of transfused RBCs.

Genetics and Biosynthesis Advanced Concepts The Lewis gene (FUT3) is linked to Se (FUT2) and H (FUT1), all located on chromosome 19. The synthesis of Lewis antigens depends on the interaction of the transferases produced by the Lewis and secretor genes. The Lewis and secretor transferases preferentially fucosylate type 1 chains, whereas the H gene (FUT1) preferentially fucosylates type 2 chains. Type 1 chain refers to the beta linkage of the number 1 carbon of galactose to the number 3 carbon of N-acetylglucosamine (GlcNAc) residue of the precursor structure (Fig. 8–1). As shown in Figure 8–2, secretor α1,2-L-fucosyltransferase adds a terminal fucose to the type 1 chain to form type 1 H. The Le allele codes for α1,4-L-fucosyltransferase, which transfers L-fucose to type 1H chain on glycoprotein or glycolipid structures to form Leb. Small amounts of Lea are made before the secretor enzyme is able to add the terminal fucose. If these individuals also have A or B genes, type 1H structures will be converted to A or B structures and the Le fucosyltransferase will then produce ALeb or BLeb (see Fig. 8–2). Individuals who are nonsecretors do not have the enzyme to convert type 1 chains in secretions to type 1H. Consequently, the type 1 precursor is available for action by the Le fucosyltransferase, with the result of Lea antigen in secretions

GAL

Type 1 GlcNAc ␤1

GAL ␤1

3

Predominant type in secretions, plasma, some tissues

3

Type 2 GAL GAL

GlcNAc ␤1

␤1

4

Predominant type on RBCs

3

Figure 8–1. Precursor type 1 and type 2 chains. The type 1 chain has a beta 1→3 linkage of the terminal galactose (Gal) to the N-acetylglucosamine (GlcNAc) of the precursor structure. The type 2 chain has a beta 1→4 linkage of the terminal galactose.

and Le(a+b–) RBCs. The Lea antigen cannot be converted to Leb because of steric hindrance from the fucose added to make Lea. Individuals with a weak Se gene, common in Asia, produce a fucosyltransferase that competes less effectively with the Le fucosyltransferase, resulting in RBCs with the Le(a+b+) phenotype.7 The Le(a+b+) phenotype is rare in European populations, and it occurs in 10% to 40% of some Asian populations.9 Mutations that result in inactivation of the fucosyltransferase, represented by the amorphic or silent le allele, are responsible for the Le(a–b–) phenotype. All Le(a–b+) individuals are ABH secretors and also secrete Lea and Leb; very little Lea will be detected in the plasma or on the RBCs. All Le(a+b–) individuals are ABH nonsecretors, yet all secrete Lea. Approximately 78% to 80% of whites are secretors, and 20% are nonsecretors. In terms of Le(a–b–) individuals, 80% are ABH secretors, and 20% are ABH nonsecretors. The interaction of Lewis, secretor, and ABO genes is summarized in Table 8–8. Lewis antigens produced in saliva and other secretions are glycoproteins, but Lewis cell-bound antigens absorbed from plasma onto the RBC membranes are glycolipids. The

Figure 8–2. Formation of Lewis antigens. Gal = galactose; GlcNAc = N-acetylglucosamine; Fuc = fucose; GalNAc = N-acetylgalactosamine.

Type 1 precursor Gal(␤1

3)GlcNAc-R

Gal(␤1

3)GlcNAc-R ␣1,4 Fuc Lea

Gal(␤1 ␣1,2 Fuc

3)GlcNAc-R ␣1,4 Fuc Leb

Le

Se Gal(␤1 ␣1,2 Fuc

3)GlcNAc-R

GalNAc(␣1

Le

Type 1H

A GalNAc(␣1

179

3)Gal(␤1 ␣1,2 Fuc Le

3)GlcNAc-R

3)Gal(␤1 ␣1,2 Fuc

3)GlcNAc-R ␣1,4 Fuc

B Gal(␣1

3)Gal(␤1 3)GlcNAc-R ␣1,2 Type 1B Fuc Le

Gal(␣1

3)Gal(␤1 ␣1,2 Fuc

Type 1A

ALeb

BLeb

3)GlcNAc-R ␣1,4 Fuc

2682_Ch08_172-215 22/05/12 11:44 AM Page 180

180

PART II

Blood Groups and Serologic Testing

Table 8–8 Antigens and Phenotypes Resulting From Interaction of Lewis, Secretor, and ABO Genes LEWIS, SECRETOR, AND ABO GENES Genes

Antigens in Secretions

RBC Phenotype

Le, Se, A/B/H

Lea, Leb, A, B, H

A, B, H, Le(a – b+)

lele, Se, A/B/H

A, B, H

A, B, H, Le(a – b –)

Le, sese, A/B/H

Lea

A, B, H, Le(a+b –)

lele, sese, A/B/H

None

A, B, H, Le(a – b –)

Le, sese, hh, A/B

Lea

Oh, Le(a+b –)

Le, Se, hh, A/B

Lea, Leb, A, B, H

A*, B*, Le(a – b+)

*para-Bombay

gastrointestinal tract is thought to be the primary source of Lewis glycolipid in plasma.5 Le(a–b–) RBCs incubated with plasma from Le(a+) or Le(b+) individuals can be converted to Le(a+b–) or Le(a–b+), respectively. With saliva as a source of Lewis substances, Le(a–b–) RBCs cannot be converted into Lewis-positive phenotypes because Lewis substances in saliva, being glycoproteins, are not adsorbed onto the RBC membranes.

Development of Lewis Antigens Depending on the genes inherited, Lea and Leb glycoproteins will be present in the saliva of newborns, but Lewis glycolipids are not detectable in the plasma until about 10 days after birth. As a result, cord blood and RBCs from newborn infants phenotype as Le(a–b–). Some can be shown to be weakly Le(a+) when tested with a potent anti-Lea or with methods more sensitive than direct agglutination. Lewis antigens will start to appear shortly after birth, with Lea developing first when the Le gene is present. The Lewis fucosyltransferase is more active than the secretor fucosyltransferase in newborns, so more type 1 chains are available for conversion to Lea. As the secretor transferase activity increases, converting type 1 to type 1H, Leb will be detected. In children who inherit both Le and Se genes, the transformation can be followed from the Le(a–b–) phenotype at birth to Le(a+b–) after 10 days to Le(a+b+) and finally to Le(a–b+), the true Lewis phenotype, after about 6 years. In contrast, children who inherit Le and sese genes phenotype as Le(a–b–) at birth and transform to Le(a+b–) after 10 days; the Le(a+b–) phenotype persists throughout life. Individuals with lele genes phenotype as Le(a–b–) at birth and for the rest of their lives.

Other Lewis Antigens Leab is present on all Le(a+b–) and Le(a–b+) RBCs and on 90% of cord RBCs. The antigen was previously known as Lex, but in 1998 the ISBT renamed it Leab.9 Anti-Leab is fairly

common and is frequently found with anti-Lea or anti-Leb. The antibody is heterogenous and occurs mainly in Le(a–b–) secretors of group A1, B, or A1B. The antigens now known as Lex and Ley are products of FUT3 on type 2 precursor chains and are not associated with the RBC surface and are not part of the Lewis blood group.9 ALeb and BLeb result from the addition of the A or B immunodominant sugar, respectively, to type 1H chain in individuals who have at least one Se and one Le allele. Se converts type 1 chains to type 1H, providing a suitable acceptor for the A and B carbohydrates (see Fig. 8–2).

The P Blood Group: P1PK (003) and Globoside (028) Systems and Related (209) Antigens Traditionally, the P blood group comprised the P, P1, and Pk antigens and, later, Luke (LKE). The biochemistry and molecular genetics, although not completely understood as yet, make it clear that at least two biosynthetic pathways and genes at different loci are involved in the development and expression of these antigens. Consequently, these antigens cannot be considered a single blood group system. Currently, in ISBT nomenclature, P1 and Pk are assigned to the P1PK blood group system (003, symbol P1PK), P is assigned to the Globoside blood group system (028, symbol GLOB), and LKE and PX2 are assigned to the Globoside collection (209, symbol GLOB). The reader will notice the confusing use of GLOB as the symbol for both a system and a collection. For simplicity in this chapter, these antigens will be referred to as the P blood group. The P blood group was introduced in 1927 by Landsteiner and Levine. In their search for new antigens, they injected rabbits with human RBCs and produced an antibody, initially called anti-P, that divided human RBCs into two groups: P+ and P–.7 In 1951, Levine and colleagues10 described anti-Tja (now known as anti-PP1Pk), an antibody to a high-prevalence antigen that Sanger11 later showed was related to the P blood group. Because anti-Tja defined an antigen common to P+ and P– cells and was made by an apparent P null individual, the original antigen and phenotypes were renamed. Anti-P became anti-P1; the P+ phenotype became P1; the P– phenotype became P2; and the rare P null individual became p. The P blood group became more complex in 1959 when Matson and coworkers12 described a new antigen, Pk. This antigen is expressed on all RBCs except those of the very rare p phenotype, but it is not readily detected unless P is absent (i.e., in the P1k and P2k phenotypes). The phenotypes, antigens, and antibodies associated with the P blood group are summarized in Table 8–9. There are two common phenotypes: P1 and P2, and three rare phenotypes: p, P1k, and P2k. The P1 phenotype describes RBCs that react with anti-P1 and anti-P; the P2 phenotype describes RBCs that do not react with anti-P1 but do react with anti-P. When RBCs are tested only with anti-P1 and not with anti-P, the phenotype should be written as P1+ (or P1) or P1–. Only when P1– RBCs are tested and found to be reactive with anti-P should they be designated as phenotype P2. RBCs of the p phenotype do not react with anti-P1, anti-P, or anti-Pk. RBCs of the P1k phenotype

2682_Ch08_172-215 22/05/12 11:44 AM Page 181

Chapter 8 Blood Group Terminology and the Other Blood Groups

181

Table 8–9 P Blood Group: Phenotypes, Antigens, and Antibodies PHENOTYPE

ANTIGENS PRESENT

POSSIBLE ANTIBODIES

PREVALENCE Whites

Blacks

P1

P1, P, Pk*

None

79%

94%

P2

P, Pk*

Anti-P1

21%

6%

p

None

Anti-PP1Pk

Rare

Rare

P1k

P1, Pk

Anti-P

Very rare

Very rare

P2k

Pk

Anti-P, anti-P1

Very rare

Very rare

*Trace amounts of Pk antigen, not detectable by agglutination test

react with anti-P1 and anti-Pk but not with anti-P. RBCs of the P2k phenotype react with anti-Pk but not with anti-P1 or anti-P. Individuals with the p phenotype (P null) are very rare: 5.8 in a million. P nulls are slightly more common in Japan, North Sweden, and in an Amish group in Ohio.1 The antibodies generally fall into two categories: clinically insignificant or potently hemolytic.

Basic Concepts The P blood group antigens, like the ABH antigens, are synthesized by sequential action of glycosyltransferases, which add sugars to precursor substances. The precursor of P1 can also be glycosylated to type 2H chains, which carry ABH antigens. P1, P, or Pk may be found on RBCs, lymphocytes, granulocytes, and monocytes; P can be found on platelets, epithelial cells, and fibroblasts. P and Pk have also been found in plasma as glycosphingolipids and as glycoproteins in hydatid cyst fluid.7 The antigens have not been identified in secretions. RBCs carry approximately 14 × 106 copies of globoside, the P structure, per adult RBC and about 5 × 105 copies of P1.9 The P blood group antigens are resistant to treatment with ficin and papain, DTT, chloroquine, and glycine-acid EDTA. Reactivity of the antibodies can be greatly enhanced by testing with enzyme-treated RBCs.

The P1 Antigen The P1 antigen is poorly expressed at birth and may take up to 7 years to be fully expressed.7 Antigen strength in adults varies from one individual to another: RBCs from some P1+ individuals are P1 strong (P1+s) and others are P1 weak (P1+w). These differences may be controlled genetically or may represent homozygous versus heterozygous inheritance of the gene coding for P1. The strength of P1 can also vary with race. Blacks have a stronger expression of P1 than whites. The rare dominant gene for the In(lu) type Lu(a–b–) RBCs, discussed in the Lutheran section, inhibits the expression of P1 so that P1 individuals who inherit this modifier gene may type serologically as P1–.

The P1 antigen deteriorates rapidly on storage. When older RBCs are typed or used as controls for typing reagents or when older RBCs are used to detect anti-P1 in serum, false-negative reactions may result.

Anti-P1 Anti-P1 is a common, naturally occurring IgM antibody in the sera of P1– individuals. Anti-P1 is typically a weak, coldreactive saline agglutinin optimally reactive at 4°C and not seen in routine testing. Stronger examples react at room temperature, and rare examples react at 37°C and bind complement, which is detected in the antiglobulin test when polyspecific (anti-IgG plus anti-C3) reagents are used. Antibody activity can be neutralized or inhibited with soluble P1 substance. If room temperature incubation is not included, antibody activity can often be bypassed altogether. Examples of anti-P1 that react only at temperatures below 37°C can be considered clinically insignificant. Because P1 antigen expression on RBCs varies and deteriorates during storage, antibodies may react only with RBCs that have the strongest expression and give inconclusive patterns of reactivity when antibody identification is performed. When anti-P1 is suspected, incubating tests at room temperature or lower or pretreating test cells with enzymes can enhance reactions to confirm specificity. Providing units that are crossmatch-compatible at 37°C and the antiglobulin phase, without typing for P1, is an acceptable approach to transfusion. Rare examples of anti-P1 that react at 37°C can cause in vivo RBC destruction; both immediate and delayed HTRs have been reported.13 Anti-P1 is usually IgM; IgG forms are rare. HDFN is not associated with anti-P1, presumably because the antibody is usually IgM and the antigen is so poorly developed on fetal RBCs.

Biochemistry Advanced Concepts The RBC antigens of the P blood group exist as glycosphingolipids. As with ABH, the antigens result from the sugars added sequentially to precursor structures. Biochemical

2682_Ch08_172-215 22/05/12 11:44 AM Page 182

182

PART II

Blood Groups and Serologic Testing

analyses have shown that the precursor substance for P1 is also a precursor for type 2H chains that carry ABH antigens. However, the genes responsible for the formation of the P1 and ABH antigens are independent. There are two distinct pathways for the synthesis of the P blood group antigens, as shown in Figure 8–3. The common precursor is lactosylceramide (or Gb2, also known as ceramide dihexose or CDH). The pathway on the figure’s left results in the formation of paragloboside and P1. Paragloboside is also the type 2 precursor for ABH. The pathway shown on the figure’s right side leads to the production of the globoside series: Pk, P, and Luke (LKE).

Genetics The gene encoding the enzyme responsible for the synthesis of Pk, a 4-α-galactosyltransferase (Gb3 or Pk synthase), was cloned independently by three research groups in 2000.14 The gene (B3GALNT1) encoding the 3-β-Nacetylgalactosaminyltransferase (Gb4 synthase) that is responsible for converting Pk to P was also cloned in 2000.14 Several mutations in both genes have been identified that result in the p and Pk phenotypes. A polymorphism in the Pk synthase was recently identified that ties the P1 and Pk antigens together at the genetic level; consequently, the P system (003), to which the P1 antigen was assigned, was renamed P1PK.3 The P1PK gene (located at chromosome 22q11.2) and the P gene (located at chromosome 3q26.1) are inherited independently. The gene for the synthesis of LKE has not yet been cloned.

Soluble P1 substances have potential use in the blood bank and are commercially available. When it is necessary to confirm antibody specificity or to identify underlying antibodies, these substances can be used to neutralize anti-P1.

Anti-PP1Pk Originally called anti-Tja, anti-PP1Pk was first described in the serum of Mrs. Jay, a p individual with adenocarcinoma of the stomach.10 Her tumor cells carried P system antigens, and the antibody was credited as having cytotoxic properties that may have helped prevent metastatic growth postsurgery (the T in the Tja refers to tumor). Anti-PP1Pk is produced by p individuals early in life without RBC sensitization and reacts with all RBCs except those of the p phenotype. Unlike antibodies made by other blood group null phenotypes, the anti-P, anti-P1, and anti-Pk components of anti-PP1Pk are separable through adsorption.7 Components of anti-PP1Pk have been shown to be IgM and IgG.7 They react over a wide thermal range and efficiently bind complement, which makes them potent hemolysins. Anti-PP1Pk has the potential to cause severe HTRs and HDFN. The antibody is also associated with an increased incidence of spontaneous abortions in early pregnancy. Although the reason for this is not fully known, it has been suggested that having an IgG anti-P component is an important factor. Women with anti-P and anti-PP1Pk and a history of multiple abortions have successfully delivered infants after multiple plasmaphereses to reduce their antibody level during pregnancy.15

Alloanti-P Other Sources of P1 Antigen and Antibody The discovery of strong anti-P1 in two P1– individuals infected with Echinococcus granulosus tapeworms led to the identification of P1 and Pk substance in hydatid cyst fluid. This fluid was subsequently used in many of the studies that identified the biochemical structures of the P blood group. Strong antibodies to P1 have also been found in patients with fascioliasis (bovine liver fluke disease) and in bird handlers.

Lactosylceramide (Gb2)

Lactotriaosylceramide

Paragloboside (type 2 precursor)

P1 antigen

Pk antigen Globotriaosylceramide (Gb3)

P antigen Globoside (Gb4)

ABH antigen LKE

Figure 8–3. Biosynthetic pathways of the P blood group antigens.

In addition to being a component of the anti-PP1Pk in p individuals (see above), anti-P is found as a naturally occurring alloantibody in the sera of Pk individuals. Its reactivity is similar to that of anti-PP1Pk in that it is usually a potent hemolysin reacting with all cells except the autocontrol and those with the p phenotype. However, it differs from anti-PP1Pk in that it does not react with cells that have the extremely rare Pk phenotype, and the individual making the antibody may type P1+. Alloanti-P is rarely seen, but because it is hemolytic with a wide thermal range of reactivity, it is very significant in transfusion. IgG class anti-P may occur and has been associated with habitual early abortion.

Autoanti-P Associated With Paroxysmal Cold Hemoglobinuria Anti-P specificity is also associated with the cold-reactive IgG autoantibody in patients with paroxysmal cold hemoglobinuria (PCH). Historically, this rare autoimmune disorder was seen in patients with tertiary syphilis; it now more commonly presents as a transient, acute condition secondary to viral infection, especially in young children. The IgG autoantibody in PCH is described as a biphasic hemolysin: In vitro, the antibody binds to RBCs in the cold, and, via complement activation, the coated RBCs lyse as they are warmed to 37°C. The autoantibody typically does not react in routine test

2682_Ch08_172-215 22/05/12 11:44 AM Page 183

Chapter 8 Blood Group Terminology and the Other Blood Groups

systems but is demonstrable only by the Donath-Landsteiner test. The etiology and diagnosis of PCH are more fully discussed in Chapter 20, “Autoimmune Hemolytic Anemias.”

Antibodies to Compound Antigens Considering the biochemical relationship of the P blood group antigens to ABH and I, it is not surprising that antibodies requiring more than one antigenic determinant have been described, including anti-IP1, -iP1, -ITP1, and -IP. Most examples are cold-reactive agglutinins.

Luke (LKE) Antigen In 1965, Tippett and colleagues16 described an antibody in the serum of a patient with Hodgkin’s lymphoma that divided the population into three phenotypes: 84% tested Luke+, 14% were weakly positive or Luke(w), and 2% were Luke–. Although this Mendelian-dominant character segregated independently of the P blood group, it was thought to be phenotypically related because the antibody reacted with all RBCs except 2% of P1 and P2 phenotypes and those having the rare p and Pk phenotypes. All individuals with the p and Pk phenotype are Luke–.

Disease Associations Several pathological conditions associated with the P blood group antigens have been described: parasitic infections are associated with anti-P1, early abortions with anti-PP1Pk or anti-P, and PCH with autoanti-P. The P system antigens also serve as receptors for P-fimbriated uropathogenic E. coli—a cause of urinary tract infections. The Pk antigen is a receptor for shiga toxins, which cause shigella dysentery and E. coli– associated hemolytic uremic syndrome. In addition, P is the receptor of human parvovirus B19. Recent studies demonstrate that Pk provides some protection against HIV infection of peripheral blood mononuclear cells.17

The I (027) System and I Antigen The existence of cold agglutinins in the serum of normal individuals and in patients with acquired hemolytic anemia has long been recognized. In 1956, Wiener and coworkers2,7 gave a name to one such agglutinin, calling its antigen I for “individuality.” The antibody reacted with most blood specimens tested. The few nonreactive I– specimens were thought to be from homozygotes for a rare gene producing the “i” antigen; the I– phenotype in adults is now called adult i. In 1960, Marsh and Jenkins18 reported finding anti-i, and the unique relationship between I and i began to unfold. I and i are not antithetical antigens. Rather, they are branched and linear carbohydrate structures, respectively, that are formed by the action of glycosyl transferases. The gene encoding the transferase that converts i active straight chains into I active branched chains has been cloned, and several mutations responsible for the rare adult i phenotype have been identified.19 The synthesis of i antigen is not controlled by this same gene. Consequently, I has been raised to

183

blood group system status (system number 027, symbol I) and the i antigen remains in the Ii collection (collection number 207, symbol I). The reader will notice the confusing use of the same ISBT symbol, capital I, for both the I system and Ii collection; in ISBT terminology, the antigen numbers provide the distinction between the I (027001) and i (207002) antigens.

The I and i Antigens Basic Concepts The antigens are best introduced by classic serologic facts. Both I and i are high-prevalence antigens, but they are expressed in a reciprocal relationship that is developmentally regulated. At birth, infant RBCs are rich in i; I is almost undetectable. During the first 18 months of life, the quantity of i slowly decreases as I increases until adult proportions are reached; adult RBCs are rich in I and have only trace amounts of i antigen. There is no true I– or i– phenotype. The strength of I and i varies from individual to individual, and the relative amount detected will depend on the example of anti-I or anti-i used. Data suggest that i reactivity on RBCs is inversely proportional to marrow transit time and RBC age in circulation. Some people appear not to change their i status after birth. They become the rare adult i. Adult i RBCs generally express more i antigen than do cord RBCs. A spectrum of Ii phenotypes and their characteristic reactivity are shown in Table 8–10. Treatment of RBCs with ficin and papain enhances reactivity of the I and i antigens with their respective antibodies. The I and i antigens are resistant to treatment with DTT and glycine-acid EDTA.

Anti-I Anti-I is a common autoantibody that can be found in virtually all sera, although testing at 4°C and/or against enzymetreated RBCs may be required to detect the reactivity.1 Consistently strong agglutination with adult RBCs and weak or no agglutination with cord or adult i RBCs define its classic activity (see Table 8–10). Autoanti-I, found in the serum of many normal healthy individuals, is benign—that is, not associated with in vivo

Table 8–10 I and i Antigens PHENOTYPE

STRENGTH OF REACTIVITY WITH Anti-I

Anti-i

Anti-IT

Adult I

Strong

Weak

Weak

Cord

Weak

Strong

Strong

Adult i

Weak

Strong

Weakest

2682_Ch08_172-215 22/05/12 11:44 AM Page 184

184

PART II

Blood Groups and Serologic Testing

RBC destruction. It is usually a weak, naturally occurring, saline-reactive IgM agglutinin with a titer less than 64 at 4°C. Stronger examples agglutinate test cells at room temperature and bind complement, which can be detected in the antiglobulin test if polyspecific reagents are used. Some examples may react only with the strongest I+ RBCs and give inconsistent reactions with panel RBCs. Incubating tests in the cold enhances anti-I reactivity and helps confirm its identity; albumin and enzyme methods also enhance anti-I reactivity. Testing enzyme-treated RBCs with slightly acidified serum may even promote hemolysis. Occasionally, benign cold autoanti-I can cause problems in pretransfusion testing. Usually, avoiding room temperature testing and using anti-IgG instead of a polyspecific antihuman globulin help to eliminate detection of cold reactive antibodies that may bind complement at lower temperatures. Cold autoadsorption to remove the autoantibody from the serum may be necessary for stronger examples; cold autoadsorbed plasma or serum can also be used in ABO typing. Pathogenic autoanti-I (e.g., the type associated with cold agglutinin syndrome) typically consists of strong IgM agglutinins with higher titers and a broad thermal range of activity, reacting up to 30° or 32°C. When peripheral circulation cools in response to low ambient temperatures, these antibodies attach in vivo and cause autoagglutination and peripheral vascular occlusion (acrocyanosis) or hemolytic anemia. Refer to Chapter 20 for more information. Pathogenic anti-I typically reacts with adult and cord RBCs equally well at room temperature and at 4°C, and antibody specificity may not be apparent unless the serum is diluted or warmed to 30°C or 37°C. Potent cold autoantibodies can also mask clinically significant underlying alloantibodies and can complicate pretransfusion testing. Procedures to deal with these problems are discussed in Chapters 9 and 20. The production of autoanti-I may be stimulated by microorganisms carrying I-like antigen on their surface. Patients with M. pneumoniae often develop strong cold agglutinins with I specificity and can experience a transient episode of acute abrupt hemolysis just as the infection begins to resolve. Alloanti-I exists as an IgM or IgG antibody in the serum of most individuals with the adult i phenotype. Although adult i RBCs are not totally devoid of I, the anti-I in these cases does not react with autologous RBCs. It has been traditional to transfuse compatible adult i units to these people, although such practice may be unnecessary, especially when the antibody is not reactive at 37°C.1 Technologists must be aware that strong autoanti-I can mimic alloanti-I: if enough autoantibody and complement are bound to a patient’s RBCs, blocking the antigenic sites, they may falsely type I-negative.

Anti-I is not associated with HDFN because the antibody is IgM, and the I antigen is poorly expressed on infant RBCs.

Anti-i Alloanti-i has never been described. Autoanti-i is a fairly rare antibody that gives strong reactions with cord RBCs and adult i RBCs and weaker reactions with adult I RBCs. Most examples of autoanti-i are IgM and react best with saline-suspended cells at 4°C. Only very strong examples of autoanti-i are detected in routine testing because standard test cells (except cord RBCs) have poor i expression (see Table 8–10). Unlike anti-I, autoanti-i is not seen as a common antibody in healthy individuals. Potent examples are associated with infectious mononucleosis (Epstein-Barr virus infections) and some lymphoproliferative disorders. High-titer autoantibodies with a wide thermal range may contribute to hemolysis, but because i expression is generally weak they seldom cause significant hemolysis. IgG anti-i has also been described and has been associated with HDFN.1

Biochemistry and Genetics Advanced Concepts An early association of I and i to ABH was demonstrated by complex antibodies involving both ABH and Ii specificity (see the “Antibodies to Compound Antigens” section). I and i antigens are precursors for the synthesis of ABO and Lewis antigens, and thus they are internal structures on these oligosaccharide chains. ABH and Ii determinants on the RBC membrane are carried on type 2 chains that attach either to proteins or to lipids. See Figure 8–4 for examples of glycolipid structures for i and I antigens. The i antigen activity is defined by at least two repeating N-acetyllactosamine [Gal(β1-4)GlcNAc(β1-3)] units in linear form. I antigen activity is associated with a branched form of i antigen. The IGnT (also known as GCNT2) gene on chromosome 6p24 encodes the N-acetylglucosaminyltransferase, which adds GlcNAc to form the branches.19,20 In summary, fetal, cord, and adult i RBCs carry predominantly unbranched chains and have the i phenotype. Normal adult cells have more branched structures and express I antigen. The gene responsible for I antigen (IGnT) codes for the branching enzyme. Family studies show that the adult i phenotype is recessive. Heterozygotes (e.g., children inheriting I from one parent and i from the other parent) have intermediate I antigen expression. Several gene mutations have been identified that result in the adult i phenotype.

Antigen

Structure

(None)

Gal(␤1-4)GlcNAc(␤1-3)Gal(␤1-4)GlcNAc(␤1-3)Gal(␤1-4)Glc-Cer

i

Gal(␤1-4)GlcNAc(␤1-3)Gal(␤1-4)GlcNAc(␤1-3)Gal(␤1-4)Glc-Cer

I

Gal(␤1-4)GlcNAc(␤1-3) Gal(␤1-4)GlcNAc(␤1-6)

Gal(␤1-4)GlcNAc(␤1-3)Gal(␤1-4)Glc-Cer

Figure 8–4. The linear and branched structures carrying i and I activity.

2682_Ch08_172-215 22/05/12 11:44 AM Page 185

Chapter 8 Blood Group Terminology and the Other Blood Groups

Other Sources of I and i Antigen

185

to react. For example, anti-IA reacts with RBCs that carry both I and A but will not react with group O, I+, or group A adult i RBCs. (Table 8–11 summarizes some common cold autoantibodies.) Anti-IH is commonly encountered in the serum of group A1 individuals. Anti-IH reacts stronger with group O and group A2 RBCs than with group A1 RBCs. AntiIH should be suspected when serum from a group A individual directly agglutinates all group O RBCs but is compatible with most group A donor units.

I and i antigens are found on the membranes of leukocytes and platelets in addition to RBCs. It is quite likely that the antigens exist on other tissue cells, much like ABH, but this has not been confirmed. I and i have also been found in the plasma and serum of adults and newborns and in saliva, human milk, amniotic fluid, urine, and ovarian cyst fluid. The antigens in secretions do not correlate with RBC expression and are thought to develop under separate genetic control. For example, the quantity of I antigen in the saliva of adult i individuals and newborns is quite high.

Disease Associations Well-known associations between strong autoantibodies and disease or microorganisms have already been discussed: antiI with cold agglutinin syndrome and M. pneumoniae, and anti-i with infectious mononucleosis. Diseases can also alter the expression of I and i antigens on RBCs. Conditions associated with increased i antigen on RBCs include those with shortened marrow maturation time or dyserythropoiesis: acute leukemia, hypoplastic anemia, megaloblastic anemia, sideroblastic anemia, thalassemia, sickle cell disease, paroxysmal nocturnal hemoglobinuria (PNH), and chronic hemolytic anemia.1,7 Except in some cases of leukemia, the increase in i on RBCs is not usually associated with a decrease in I antigen; the expression of I antigen can appear normal or sometimes enhanced. Chronic dyserythropoietic anemia type II or hereditary erythroblastic multinuclearity with a positive acidified serum test (HEMPAS) is associated with much greater i activity on RBCs than control cord RBCs. HEMPAS RBCs are very susceptible to lysis with both anti-i and anti-I, and lysis by anti-I appears to be the result of increased antibody uptake and increased sensitivity to complement.1 In Asians, the adult i phenotype has been associated with congenital cataracts.20

The IT Antigen and Antibody In 1965, Curtain and coworkers21 reported a cold agglutinin in Melanesians that did not demonstrate classical I or i specificity. In 1966, Booth and colleagues22 confirmed these observations and carefully described the agglutinin’s reactivity. This agglutinin reacted strongly with cord RBCs, weakly with normal adult RBCs, and most weakly with adult i RBCs. They concluded that the agglutinin recognizes a transition state of i into I and designated the specificity IT (T for “transition”). However, detection of IT on fetal RBCs ranging in age from 11 to 16 weeks does not support this hypothesis.23 This benign IgM anti-IT was frequently found in two populations: Melanesians and the Yanomama Indians in Venezuela. Whether it is associated with an organism or parasite in these regions is unknown. Examples of IgM and IgG anti-IT reacting preferentially at 37°C have also been found in patients with warm autoimmune hemolytic anemia, with a special association with Hodgkin’s disease.23

Antibodies to Compound Antigens

The MNS (002) System

Many other I-related antibodies have been described: antiIA, -IB, -IAB, -IH, -iH, -IP1, -ITP1, -IHLeb, and -iHLeb. Bearing in mind the close relationship of I to the biochemical structures of ABH, Lewis, and P antigens, it is not surprising to find antibodies that recognize compound antigens. These specificities are not mixtures of separable antibodies; rather, both antigens must be present on the RBCs for the antibody

Following the discovery of the ABO blood group system, Landsteiner and Levine began immunizing rabbits with human RBCs, hoping to find new antigen specificities. Among the antibodies recovered from these rabbit sera were anti-M and anti-N, both of which were reported in 1927.7 Data from family studies suggested that M and N were

Table 8–11 Typical Reactions of Some Cold Autoantibodies* ANTIBODY

A1 ADULT

A2 ADULT

B ADULT

O ADULT

O CORD

A CORD

Oh ADULT

Anti-I

++++

++++

++++

++++

0/+

0/+

++++

(0)

Anti-i

0/+

0/+

0/+

0/+

++++

++++

0/+

++++

Anti-H

0/+

++

+++

++++

+++

0/+

(0)

+++

Anti-IH

0/+

++

+++

++++

0/+

0/+

(0)

(0)

Anti-IA

++++

+++

0/+

0/+

0/+

0/+

(0)

(0)

*Reactions vary with antibody strength; very potent examples may need to be diluted before specificity can be determined. 0 = negative; + = positive

O i ADULT

2682_Ch08_172-215 22/05/12 11:44 AM Page 186

186

PART II

Blood Groups and Serologic Testing

antithetical antigens. In 1947, after the implementation of the antiglobulin test, Walsh and Montgomery discovered S, a distinct antigen that appeared to be genetically linked to M and N. Its antithetical partner, s, was discovered in 1951. Family studies (and later, molecular genetics) demonstrated the close linkage between the genes controlling M, N, and S, s antigens. There is a disequilibrium in the expression of S and s with M and N. In whites, the common haplotypes were calculated to appear in the following order of relative frequency: Ns > Ms > MS > NS.1,7 The prevalence of the common MN and Ss phenotypes are listed in Table 8–12. In 1953, an antibody to a high-prevalence antigen, U (for almost universal distribution), was named by Weiner. The observation by Greenwalt and colleagues24 that all U– RBCs were also S–s– resulted in the inclusion of U into the system. Forty-six antigens have been included in the MNS system, making it almost equal to Rh in size and complexity (Table 8–13). Most of these antigens are of low prevalence and were discovered in cases of HDFN or incompatible crossmatch. Others are high-prevalence antigens. Antibodies to these low- and high-prevalence antigens are not commonly encountered in the blood bank. The genes encoding the MNS antigens are located on chromosome 4. The MNS blood group system has been assigned the ISBT number 002 (symbol MNS), second after ABO.

M and N Antigens Basic Concepts The M and N antigens are found on a well-characterized glycoprotein called glycophorin A (GPA), the major RBC sialic acid–rich glycoprotein (sialoglycoprotein, SGP). The M and N antigens are antithetical and differ in their amino acid residues at positions 1 and 5 (Fig. 8–5). M is defined by serine at position 1 and glycine at position 5; N has leucine and glutamic acid at these positions, respectively. The antibody reactivity may also be dependent on adjacent carbohydrate chains, which are rich in sialic acid. There are about 106 copies of GPA per RBC.13 The antigens are well developed at birth. Because M and N are located at the outer end of GPA, they are easily destroyed by the routine blood bank enzymes ficin, papain, and bromelin and by the less common enzymes trypsin and pronase. The antigens are also destroyed by ZZAP, a combination of DTT and papain or ficin, but they are not affected by DTT alone, 2-aminoethylisothiouronium bromide (AET), α-chymotrypsin, chloroquine, or glycine-acid EDTA treatment. Treating RBCs with neuraminidase, which cleaves sialic acid (also known as neuraminic acid or NeuNAc), abolishes reactivity with only some examples of antibody. M and N antibodies are heterogeneous; some may recognize only specific amino acids, but others recognize both amino acids and carbohydrate chains.

Table 8–12 Prevalence of Common MN and Ss Phenotypes PHENOTYPE

WHITES (%)

BLACKS (%)

M+N–

28

26

M+N+

50

44

M–N+

22

30

S+s–

11

3

S+s+

44

28

S–s+

45

69

S–s–U–

99.9

Kpa, Kpc

1958

Ku

5

KEL5

> 99.9

Jsa

6

KEL6

< 0.1 whites 20 blacks

Jsb

1958

Jsb

7

KEL7

> 99.9 whites 99 blacks

Jsa

1963

Ula

10

KEL10

< 3 Finns

Côté

11

KEL11

> 99.9

Boc

12

KEL12

> 99.9

1973

SGRO

13

KEL13

> 99.9

1973

San

14

KEL14

> 99.9

k-like

16

KEL16

99.8

Wka

17

KEL17

0.3

VM

18

KEL18

> 99.9

1957

1968 K17

K24

1971

1973 1976

K11

1974 1975 Continued

2682_Ch08_172-215 22/05/12 11:44 AM Page 192

192

PART II

Blood Groups and Serologic Testing

Table 8–14 Kell System Antigens—cont’d NAME

NUMERIC TERMINOLOGY

ISBT NUMBER

PREVALENCE (%)

ANTITHETICAL ANTIGEN(S)

YEAR DISCOVERED

Sub

19

KEL19

> 99.9

1979

Km

20

KEL20

> 99.9

1979

Kpc

21

KEL21

< 0.1

Ikar

22

KEl22

> 99.9

1982

Centauro

23

KEL23

< 0.01

1987

CL

24

KEL24

99.9

1995

KEL27

> 99.9

1994

VONG

KEL28

< 0.1

2003

KALT

KEL29

> 99.9

2006

KTIM

KEL30

> 99.9

2006

KYO

KEL31

< 0.1

2006

KUCI

KEL32

> 99.9

2007

KANT

KEL33

> 99.9

2007

KASH

KEL34

> 99.9

2007

KELP

KEL35

> 99.9

2010

RAZ

K27

Kpa, Kpb

1945

K14

1985

Obsolete: K8, K9, K15

Basic Concepts Kell blood group antigens are found only on RBCs. They have not been found on platelets or on lymphocytes, granulocytes, or monocytes. The associated Xk protein is found in erythroid tissues and in other tissues, such as brain, lymphoid organs, heart, and skeletal muscle.30 The K antigen can be detected on fetal RBCs as early as 10 weeks and is well developed at birth. The k antigen has been detected at 7 weeks. The total number of K antigen sites per RBC is quite low: only 3,500 up to 18,000 sites per RBC.9 Despite its lower quantity, K is very immunogenic. The antigens are not denatured by the routine blood bank enzymes ficin and papain but are destroyed by trypsin and chymotrypsin when used in combination.7 Thiol-reducing agents, such as 100 to 200 mM DTT, 2-mercaptoethanol (2-ME), AET, and ZZAP (which contains DTT in addition to enzyme), destroy Kell antigens but not Kx. Glycine-acid EDTA (an IgG-removal agent) also destroys Kell antigens. The prevalence of common Kell phenotypes are listed in Table 8–15. There are five sets of antithetical antigens; antithetical relationships have not been established for the other high- and low-prevalence antigens. Some of the Kell antigens (e.g., Jsb) are more prevalent in certain populations.

Table 8–15 Prevalence of Common Kell System Phenotypes PHENOTYPE

WHITES (%)

BLACKS (%)

K–k+

91

96.5

K+k+

8.8

3.5

K+k–

0.2

< 0.1

Kp(a+b–)

< 0.1

Kp(a+b+)

2.3

Rare

Kp(a–b+)

97.7

100

Js(a+b–)

1

Js(a+b+)

Rare

19

Js(a–b+)

100

80

K and k Antigens Excluding ABO, K is rated second only to D in immunogenicity. Most anti-K appear to be induced by pregnancy and transfusion.7 Fortunately, the prevalence of K antigen is low (9% in whites), and the chance of receiving a K+ unit is small. If anti-K develops, compatible units are easy to find.

2682_Ch08_172-215 22/05/12 11:44 AM Page 193

Chapter 8 Blood Group Terminology and the Other Blood Groups

Antibodies to k antigen are seldom encountered. Only 2 in 1,000 individuals lack k and are capable of developing the antibody. The likelihood that these few individuals will receive transfusions and become immunized is even less.

Kpa, Kpb, and Kpc Antigens Alleles Kpa and Kpc are low-prevalence mutations of their high-prevalence partner Kpb. The Kpa antigen is found in about 2% of whites. The Kpa gene is associated with suppression of other Kell antigens on the same molecule, including k and Jsb.7 The effect appears to result from a reduced amount of the Kell glycoprotein (produced by the Kpa allele) inserted in the RBC membrane. The Kpc antigen is even more rare.

Jsa and Jsb Antigens The Jsa antigen, antithetical to the high-prevalence antigen Jsb, is found in about 20% of blacks but in fewer than 0.1% of whites.9 The prevalence of Jsa in blacks is almost 10 times greater than the prevalence of the K antigen in blacks. Jsa and Jsb were linked to the Kell system when it was discovered that Ko RBCs were Js(a–b–).

Anti-K Outside the ABO and Rh antibodies, anti-K is the most common antibody seen in the blood bank. Anti-K is usually IgG and reactive in the antiglobulin phase, but some examples agglutinate saline-suspended RBCs. The antibody is usually made in response to antigen exposure through pregnancy and transfusion and can persist for many years. Naturally occurring IgM examples of anti-K are rare and have been associated with bacterial infections. Marsh and colleagues31 studied an IgM anti-K in an untransfused 20-day-old infant with an E. coli O125:B15 infection whose mother did not make anti-K. The organism was shown to have a somatic K-like antigen that reacted with the infant’s antibody, so the bacterial antigen was thought to have been the stimulus. The antibody disappeared after recovery. Some examples of anti-K react poorly in methods incorporating low-ionic media, such as LISS, and in some automated systems. The most reliable method of detection is the indirect antiglobulin test. The potentiating medium, PEG, may increase reactivity. Anti-K has been implicated in severe HTRs. Although some examples of anti-K bind complement, in vivo RBC destruction is usually extravascular via the macrophages in the spleen. Anti-K is also associated with severe HDFN. The antibody titer does not always accurately predict the severity of disease; stillbirth has been seen with anti-K titers as low as 64. Fetal anemia in anti-K HDFN is associated with suppression of erythropoiesis due to destruction of erythroid precursor cells, which can be additional to destruction of circulating antigen-positive RBCs, as seen in anti-D HDFN. Kell glycoprotein is expressed on fetal RBCs at a much earlier stage of erythropoiesis than Rh antigens.32 When a pregnant woman is identified as making anti-K, it is prudent to type

193

the father for the K antigen. If he’s K+, the fetus should be monitored carefully for signs of HDFN.

Antibodies to Kpa, Jsa, and Other Low-Prevalence Kell Antigens Antibodies to the low-prevalence Kell antigens are rare because so few people are exposed to these antigens. Because routine antibody detection RBCs do not carry low-prevalence antigens, the antibodies are most often detected through unexpected incompatible crossmatches or cases of HDFN. The serologic characteristics and clinical significance of these antibodies parallel anti-K. The original anti-Kpa was naturally occurring, but most antibodies result from transfusion or pregnancy.

Antibodies to k, Kpb, Jsb, and Other High-Prevalence Kell Antigens Antibodies to high-prevalence Kell system antigens are rare because so few people lack these antigens. They also parallel anti-K in serologic characteristics and clinical significance. The high-prevalence antibodies are easy to detect but difficult to work with, because most blood banks do not have the antigen-negative panel cells needed to exclude other alloantibodies, nor do they have typing reagents to phenotype the patient’s RBCs. Testing an unidentified high-prevalence antibody against DTT- or AET-treated RBCs is a helpful technique: Reactivity that is abolished with DTT or AET treatment suggests that the antibody may be related to the Kell system and enables the technologist to exclude common alloantibodies. Caution is needed before assigning Kell system specificity until antigen-negative RBCs are tested, because DTT also denatures JMH and high-prevalence antigens in the LW, Lutheran, Dombrock, Cromer, and Knops systems. Finding compatible units for transfusion can be difficult; siblings and rare-donor inventories are the most likely sources. Patients with antibodies to high-prevalence antigens should be encouraged to donate autologous units and, if possible, to participate in a rare-donor program.

Biochemistry Advanced Concepts The Kell antigens are located on a glycoprotein that consists of 731 amino acids and spans the RBC membrane once. The N-terminal domain is intracellular, and the large external C-terminal domain is highly folded by disulfide linkages (Fig. 8–8). The Kell glycoprotein is covalently linked with another protein, called Xk, by a single disulfide bond. The Xk protein (440 amino acids) is predicted to span the RBC membrane ten times. Kell antigen expression is dependent upon the presence of the Xk protein. The Kell glycoprotein is a member of the neprilysin (M13) family of zinc endopeptidases associated with the cleavage of big endothelins, but how this relates to the physiological role of the Kell glycoprotein remains unclear. The structure of the Xk protein suggests a membrane

2682_Ch08_172-215 22/05/12 11:44 AM Page 194

194

PART II

Blood Groups and Serologic Testing

transport protein. The absence of Xk results in McLeod syndrome (see the “McLeod Phenotype and Syndrome” section below).

Genetics The KEL gene, located on chromosome 7 (at 7q34), is organized into 19 exons of coding sequence. Single base mutations encoding amino acid substitutions are responsible for the different Kell antigens. Several different mutations (e.g., point, frameshift, or splice site mutations) have been found that result in the rare null phenotype Ko.7,9 No Kell haplotype has been shown to code for more than one low-prevalence antigen. People who test positive for two low-prevalence Kell antigens have always been found to carry the encoding alleles on opposite chromosomes. For example, someone who types Kp(a+) and Js(a+) is genetically kKpaJsb on one chromosome and kKpbJsa on the other. The XK gene, which encodes the Kx antigen, is independent of KEL and is located on the short arm of the X chromosome at position Xp21.1.7

The Kx Antigen Kx is present on all RBCs except those of the rare McLeod phenotype (see the “McLeod Phenotype and Syndrome” section below). Ko and Kmod phenotype RBCs have increased Kx antigen.7 When Kell antigens are denatured with AET or DTT, the expression of Kx increases.

The Ko Phenotype and Anti-Ku(K5) Ko RBCs lack expression of all Kell antigens. Ko RBCs have no membrane abnormality and survive normally in circulation. The phenotype is rare; data suggest a frequency of 1:25,000 in whites.7 Immunized individuals with the Ko phenotype typically make an antibody called anti-Ku (K5) that recognizes the “universal” Kell antigen (Ku) present on all RBCs except Ko. Kell COOH

Kx

S-S

NH2 NH2 COOH Figure 8–8. Proposed structures for Kell and Kx proteins. The two proteins are linked through one disulfide bond. The conformation of the large external domain of the Kell glycoprotein is unknown; 15 cysteine residues suggest the presence of disulfide bonds and extensive folding.

Anti-Ku appears to be a single specificity and cannot be separated into components. Anti-Ku has caused both HDFN and HTRs.7 Because Ko RBCs are negative for k, Kpb, Jsb, and so forth, they are very useful in investigating complex antibody problems. They can help confirm a Kell system specificity or rule out other underlying specificities. When Ko RBCs are not available, they can be made artificially by treating normal RBCs with DTT, AET, or glycine-acid EDTA.

The McLeod Phenotype and Syndrome In 1961, Allen and coworkers33 described a young male medical student who initially appeared to be Kell null but who demonstrated weak expression of k, Kpb, and Jsb detectable by adsorption-elution methods. This unusual phenotype was called McLeod, after the student. The McLeod phenotype is very rare. All who have it are male, and inheritance is X-linked through a carrier mother. McLeod phenotype RBCs lack Kx and another highprevalence antigen, Km, and have marked depression of all other Kell antigens. The weakened expression of the Kell antigens is designated by a superscript w for “weak”—for example, K–k+w Kp(a–b+w). The McLeod phenotype has been associated with several mutations and deletions at the XK locus. A significant proportion of the RBCs in individuals with the McLeod phenotype are acanthocytic (having irregular shapes and protrusions) with decreased deformability and reduced in vivo survival. As a result, individuals with the McLeod phenotype have a chronic but often well-compensated hemolytic anemia characterized by reticulocytosis, bilirubinemia, splenomegaly, and reduced serum haptoglobin levels. Individuals with the McLeod phenotype have a variety of muscle and nerve disorders that, together with the serologic and hematologic picture, are collectively known as the McLeod syndrome, one of the neuroacanthocytosis syndromes. McLeod individuals develop a slow, progressive form of muscular dystrophy between ages 40 and 50 years and cardiomegaly (leading to cardiomyopathy). The associated neurological disorder presents initially as areflexia (a lack of deep tendon reflexes) and progresses to choreiform movements (well-coordinated but involuntary movements). These individuals also have elevated serum creatinine phosphokinase levels of the MM type (cardiac/skeletal muscle) and carbonic anhydrase III levels. In 1971, Giblett and colleagues made an association between the rare Kell phenotypes, including the McLeod phenotype, and the rare X-linked chronic granulomatous disease (CGD).34 CGD is characterized by the inability of phagocytes to make NADH oxidase, an enzyme important in generating H2O2, which is used to kill ingested bacteria. Afflicted children can die at an early age from overwhelming infections if not treated. Not all males with the McLeod phenotype have CGD, nor do all patients with CGD have the McLeod phenotype. At one time it was suggested that CGD was caused by a lack of Kx on white blood cells, and several alleles at the XK locus were proposed to explain Kx expression on McLeod RBCs and

2682_Ch08_172-215 22/05/12 11:44 AM Page 195

Chapter 8 Blood Group Terminology and the Other Blood Groups

CGD white blood cells. More recent data have shown that this theory is not valid. The XK gene resides on the X chromosome near deletions associated with CGD, Duchenne muscular dystrophy, and retinitis pigmentosa, in the Xp21 region. The expression of Kx in women who are carriers of the McLeod phenotype follows the Lyon hypothesis, which states that in early embryo development, one X chromosome randomly shuts down in female cells that have two. All cells descending from the resulting cell line express only the allele on the active chromosome. Hence, McLeod carriers exhibit two RBC populations: one having Kx and normal Kell antigens, the other having the McLeod phenotype and acanthocytosis. The percentage of McLeod phenotype RBCs in carriers varies from 5% to 85%.1 McLeod males with CGD make anti-Kx + Km, which reacts strongly with Ko RBCs, weaker with normal Kell phenotype RBCs, and not at all with McLeod phenotype RBCs. Anti-Km is made by McLeod males without CGD. There are rare reports of a McLeod male without CGD who has made anti-Kx + Km.35 The expression of Kell antigens on RBCs with common, McLeod, and Ko phenotypes is summarized in Table 8–16.

Altered Expressions of Kell Antigens Weaker-than-normal Kell antigen expression is associated with the McLeod phenotype and the suppression by the Kpa gene (cis-modified effect) on Kell antigens. Depressed Kell antigens are also seen on RBCs with the rare Gerbichnegative phenotypes Ge: –2, –3, 4 and Ge: –2, –3, –4. The phenotypic relationship between Gerbich and Kell is not understood. The umbrella term Kmod is used to describe other phenotypes with very weak Kell expression, often requiring adsorption-elution tests for detection. As a group, these RBCs have a reduced amount of Kell glycoprotein and enhanced Kx expression. Some Kmod individuals make an antibody that resembles anti-Ku but does not react with other Kmod RBCs (unlike anti-Ku made by Ko individuals). Patients with autoimmune hemolytic anemia, in which the autoantibody is directed against a Kell antigen, may have depressed expression of that antigen. Antigen strength returns to normal when the anemia resolves and the DAT becomes negative. This phenomenon appears to be more common in the Kell system than in others.1 Finally, RBCs may appear to acquire Kell antigens. McGinnis and coworkers36 described a K– patient who acquired a K-like antigen during a Streptococcus faecium

infection. Cultures containing the disrupted organism converted K– cells to K+ but bacteria-free filtrates did not.

Autoantibodies Most Kell autoantibodies are directed against undefined high-prevalence Kell antigens, but identifiable autoantibodies to K, Kpb, and K13 have been reported. Mimicking specificities have also been reported, such as when an apparent anti-K is eluted from DAT+ K– RBCs and the anti-K in the eluate can be adsorbed onto K– RBCs.

The Duffy (008) System The Duffy blood group system was named for Mr. Duffy, a multiply transfused hemophiliac who in 1950 was found to have the first described example of anti-Fya. One year later, the antibody defining its antithetical antigen, Fyb, was found in the serum of a woman who had had three pregnancies. In 1955, Sanger and colleagues37 reported that the majority of African Americans tested were Fy(a–b–). The gene responsible for this null phenotype was called Fy. FyFy appeared to be a common genotype in blacks, especially in Africa; the gene is exceedingly rare in whites. In 1975, it was observed that Fy(a–b–) RBCs resist infection in vitro by the monkey malaria organism Plasmodium knowlesi. It was later shown that Fy(a–b–) RBCs also resist infection by P. vivax (one of the organisms causing malaria in humans).37 This discovery provides an explanation for the predominance of the Fy(a–b–) phenotype in persons originating from West Africa. Antibodies to other antigens in the Duffy blood group system, Fy3, Fy5, are rarely encountered. RBCs that are Fy(a–b–) are also Fy: –3, –5. Fy5 is also not present on Rhnull RBCs, regardless of the Fya or Fyb status of those RBCs. The Duffy blood group system is designated by the symbol FY or 008 by the ISBT.

Fya and Fyb Antigens Basic Concepts The Duffy antigens most important in routine blood bank serology are Fya and Fyb. They can be identified on fetal RBCs as early as 6 weeks gestational age and are well developed at birth. There are about 13,000 to 14,000 Fya

Table 8–16 Expression of Kell Antigens on RBCs With Common, Ko, and McLeod Phenotypes PHENOTYPE

195

RBC ANTIGEN EXPRESSION

POSSIBLE ANTIBODY

Kell Antigens

Km

Kx

Common

k, Kpb, Jsb, K11 . . .

Normal

Weak

Alloantibody

Ko

None

None

Increased

Anti-Ku

McLeod

Trace k, Kpa, Jsb, K11 . . .

None

None

Anti-Kx + Km (CGD) Anti-Km (non-CGD)

2682_Ch08_172-215 22/05/12 11:44 AM Page 196

196

PART II

Blood Groups and Serologic Testing

or Fyb sites on Fy(a+b–) and Fy(a–b+) RBCs, respectively; there are half that number of Fya sites on Fy(a+b+) RBCs.7 The antigens have not been found on platelets, lymphocytes, monocytes, or granulocytes, but they have been identified in other body tissues, including brain, colon, endothelium, lung, spleen, thyroid, thymus, and kidney cells.9 The prevalence of the common phenotypes in the Duffy system are given in Table 8–17. The disparity in distribution in different races is notable. Fya and Fyb antigens are destroyed by common proteolytic enzymes, such as ficin, papain, bromelin, and chymotrypsin, and by ZZAP (which contains either papain or ficin in addition to DTT); they are not affected by DTT alone, AET, or glycine-acid EDTA treatment. Neuraminidase may reduce the molecular weight of Fya and Fyb, but it does not destroy antigenic activity and neither does purified trypsin.

Anti-Fya and Anti-Fyb Anti-Fya is a common antibody and is found as a single specificity or in a mixture of antibodies. Anti-Fya occurs three times less frequently than anti-K. Anti-Fyb is 20 times less common than anti-Fya and often occurs in combination with other antibodies. The antibodies are usually IgG and react best at the antiglobulin phase. Rare examples of anti-Fya and anti-Fyb bind complement. A few examples are saline agglutinins. Antibody activity is enhanced in a low ionic strength medium. Because anti-Fya and anti-Fyb do not react with enzyme-treated RBCs, this is a helpful technique when multiple antibodies are present. Some examples of anti-Fya and anti-Fyb show dosage, reacting more strongly with RBCs that have a double dose than RBCs from heterozygotes. It must be remembered that some reagent RBCs that appear to be from homozygotes (and have a double dose of either Fya or Fyb) may actually be from heterozygotes if they are from black donors; a silent allele, Fy, is commonly found in blacks. For example, Fy(a+b–) RBCs will have a double dose of Fya if they are from a white FyaFya donor but will have a single dose of Fya if they are from a black donor who is genetically FyaFy. Additional phenotypic markers commonly found in black donors can give a clue to the possible presence of the silent Fy allele: Ro, S–s–, V+VS+, Js(a+), Le(a–b–).

Anti-Fya and anti-Fyb have been associated with acute and delayed HTRs. Once the antibody is identified, Fy(a–) or Fy(b–) blood must be given; finding such units in a random population is not difficult. For example, one in three random units of blood is Fy(a–) and one in five random units of blood is Fy(b–). Anti-Fya and anti-Fyb are associated with HDFN that ranges from mild to severe. Rare autoantibodies with mimicking Fya and Fyb specificity have been reported—for example, anti-Fyb that can be adsorbed onto and eluted from Fy(a+b–) RBCs. Issitt and Anstee1 suggest that these may represent alloantibodies with “sloppy” specificity made early in an immune response.

Biochemistry Advanced Concepts Enzymes, membrane solubilization methods, immunoblotting, radiolabeling, and amino acid sequencing have all been used to study the biochemistry of Duffy antigens.1 Duffy antigens reside on a glycoprotein of 336 amino acids that has a relative mass of 36 kD and two N-glycosylation sites (Fig. 8–9).38 The glycoprotein is predicted to traverse the cell membrane seven times and has two predicted disulfide bridges. The amino acid at position 42 on the Duffy glycoprotein defines the Fya and Fyb polymorphism: Fya has glycine, and Fyb has aspartic acid. The Fy3 epitope, as defined by monoclonal antibody, is on the third extracellular loop, and Fy6 appears to involve amino acids 19 through 25.38 The Duffy glycoprotein is a member of the superfamily of chemokine receptors and is known as the Duffy antigen receptor for chemokines (DARC). Thus, in addition to being a receptor for the malaria parasite P. vivax, the Duffy glycoprotein binds a variety of proinflammatory cytokines. Genetics In 1968, the Duffy gene was linked to a visible, inherited abnormality of chromosome 1, thus becoming the first human gene to be assigned to a specific chromosome. The gene is located near the centromere on the long arm of chromosome 1 at position 1q23.2. The Fy locus is syntenic to the Rh locus, which is located near the tip of the short arm; that is, they

Table 8–17 Prevalence of Common Duffy Phenotypes

Fy6

[

PHENOTYPE Fy(a+b–)

17

9

90.8

Fy(a+b+)

49

1

8.9

Fy(a–b+)

34

22

0.3

Fy(a–b–)

Very rare

68

Fy3

Fya/Fyb S

SS

S

CHINESE (%)

WHITES (%)

NH2

[

AFRICAN AMERICANS (%)

COOH Figure 8–9. Proposed structure for the Duffy protein. Disulfide bonds probably link the NH2 terminal domain and the third loop and the first and second loop.

2682_Ch08_172-215 22/05/12 11:44 AM Page 197

Chapter 8 Blood Group Terminology and the Other Blood Groups

are on the same chromosome, but they are far enough apart that linkage cannot be demonstrated and serologically they appear to segregate independently. There are three common alleles at the Fy locus: Fya, Fyb, and Fy. Fya and Fyb encode the antithetical antigens Fya and Fyb, respectively, and Fy is a silent allele and is the major allele in blacks. The Fy gene in Fy(a–b–) blacks is an Fyb variant with a change in the promoter region of the gene, which disrupts the binding site for mRNA transcription in the RBC.9 Consequently, Fy(a–b–) blacks do not express Fyb on their RBCs but express Fyb in other tissues. The presence of Fyb in tissues presumably precludes the recognition of Fyb as foreign; thus, no anti-Fyb is made by these individuals. A molecular analysis of Fy(a–b–) whites revealed different mutations. These individuals carry no Duffy protein on their RBCs or on other tissues and thus can form anti-Fyb and anti-Fy3. Typing for Duffy antigens has been performed on the RBCs of chimpanzees, gorillas, and old- and new-world monkeys. The results suggest that Fy3 developed first, then Fyb, and that Fya arose during human evolution.9

Fyx Fyx was described in 1965 as a new allele at the Fy locus. It does not produce a distinct antigen but rather is an inherited weak form of Fyb that reacts with some examples of anti-Fyb. Fyx has been described in white populations. Individuals with Fyx may type Fy(b–), but their RBCs adsorb and elute anti-Fyb. They also have depressed expression of their Fy3 and Fy5 antigens. The decreased expression of Fyb due to Fyx appears to be related to a reduced amount of Duffy glycoprotein on the surface of RBCs.39 There is no anti-Fyx.

Fy3 Antigen and Antibody In 1971, anti-Fy3 was found in the serum of an Fy(a–b–) white Australian female. It reacted with all RBCs tested except those of the Fy(a–b–) phenotype. Because it was an inseparable anti-FyaFyb, it was thought to react with an antigenic determinant or precursor common to both Fya and Fyb and was called Fy3. Unlike Fya and Fyb, the Fy3 antigen is not destroyed by enzymes. Anti-Fy3 is a rare antibody made by Fy(a–b–) individuals who lack the Duffy glycoprotein. The Fy(a–b–) phenotype has been found in whites, Cree Indian families, and blacks.1 Blacks with the Fy(a–b–) phenotype rarely make anti-Fy3. Some blacks who make anti-Fy3 initially make anti-Fya.7

Fy5 Antigen and Antibody In 1973, Colledge and coworkers40 discovered anti-Fy5 in the serum of an Fy(a–b–) black child who later died of leukemia. Initially it was thought to be a second example of anti-Fy3, because it reacted with all Fy(a+) or Fy(b+) RBCs but not with Fy(a–b–) cells. The antibody differed

197

in that it reacted with the cells from an Fy(a–b–)Fy:–3 white female, but it did not react with Fy(a+) or Fy(b+) Rhnull RBCs and reacted only weakly with Fy(a+) or Fy(b+) D__ RBCs. Sometimes, sera containing anti-Fy5 also contain antiFya. Several examples of anti-Fy5 have been reported in multiply transfused Fy(a–b–) sickle cell patients with a mixture of other antibodies. The molecular structure of Fy5 is not known, but it appears to be the result of interaction between the Rh complex and the Duffy glycoprotein. People who are Fy(a–b–) or Rhnull do not make Fy5 antigen and are at risk of making the antibody, although few do. Like Fy3, Fy5 is not destroyed by enzymes.

The Kidd (009) System The Kidd blood group is a simple and straightforward system consisting of only three antigens. In 1951, Allen and colleagues41 reported finding an antibody in the serum of Mrs. Kidd, whose infant had HDFN. The antibody, named anti-Jka, reacted with 77% of Bostonians. Its antithetical partner, Jkb, was found 2 years later. The null phenotype Jk(a–b–) was described in 1959. The propositus made an antibody to a high-prevalence antigen called Jk3, which is present on any RBC positive for Jk a or Jkb. No other antigens associated with the Kidd system have been described. The Kidd system is designated by the symbol JK or 009 by the ISBT. It has special significance to routine blood banking because of its antibodies, which can be difficult to detect and are a common cause of HTRs.

Jka and Jkb Antigens Basic Concepts Jka and Jkb are antigens commonly found on RBCs of most individuals. Table 8–18 summarizes the prevalence of the four known phenotypes. There are notable differences in antigen frequency among various races: 91% of blacks and 77% of whites are Jk(a+); 57% of blacks and only 28% of whites are Jk(b–). Jka and Jkb antigens are well developed on the RBCs of neonates. Jka has been detected on fetal RBCs as early as 11 weeks; Jkb has been detected at 7 weeks.7 Although this early development of Kidd antigens contributes to the potential for HDFN, anti-Jka and anti-Jkb are only rarely responsible for severe HDFN. Jk(a+b–) RBCs carry 14,000 antigen sites per cell.7 The Kidd antigens are not very immunogenic. Kidd antigens are not denatured by papain or ficin; treatment of RBCs with enzymes generally enhances reactivity with Kidd antibodies. Kidd antigens are also not affected by chloroquine, DTT, AET, or glycine-acid EDTA. The antigens are not found on platelets, lymphocytes, monocytes, or granulocytes.

2682_Ch08_172-215 22/05/12 11:44 AM Page 198

198

PART II

Blood Groups and Serologic Testing

Table 8–18 Prevalence of Kidd Phenotypes PHENOTYPE

WHITES (%)

BLACKS (%)

ASIANS (%)

Jk(a+b–)

28

57

23

Jk(a+b+)

49

34

50

Jk(a–b+)

23

9

27

Jk(a–b–)

Exceedingly rare

Exceedingly rare

0.9 Polynesians

Anti-Jka and Anti-Jkb Kidd antibodies have a notorious reputation in the blood bank. They demonstrate dosage, are often weak, and are found in combination with other antibodies, all of which make them difficult to detect. Anti-Jka is more frequently encountered than anti-Jkb, but neither antibody is common. The antibodies are usually IgG (antiglobulin reactive) but may also be partly IgM and are made in response to pregnancy or transfusion. The ability of Kidd antibodies to show dosage can confound inexperienced serologists. Many anti-Jka and anti-Jkb react more strongly with RBCs that carry a double dose of the respective antigen and may not react with Jk(a+b+) RBCs. An anti-Jka that reacts only with Jk(a+b–) RBCs can give inconclusive panel results and appear compatible with Jk(a+b+) cells. Readers are urged to rule out anti-Jka and anti-Jkb only with Jk(a+b–) and Jk(a–b+) panel cells, respectively, and to type all crossmatch-compatible units with commercial antisera. To ensure that antisera can indeed detect weak expressions of the antigen, Jk(a+b+) RBCs should be tested in parallel as the positive control. Antibody reactivity can also be enhanced by using LISS or PEG (to promote IgG attachment), by using four drops of serum instead of two (to increase the antibody-to-antigen ratio), or by using enzymes such as ficin or papain. In vitro hemolysis can sometimes be observed with enzyme-treated RBCs if serum is tested; antigen dose may influence this hemolytic activity.1 Many examples of the Kidd antibodies bind complement. Rare examples are detected only by the complement they bind (i.e., they are nonreactive in antiglobulin tests using anti-IgG reagents). Testing serum (rather than plasma) and using polyspecific reagents with both anti-IgG and anticomplement can be helpful in these situations.1 The titer of anti-Jka or anti-Jkb quickly declines in vivo. A strong antibody identified following a transfusion reaction may be undetectable in a few weeks or months.1 This confirms the need to check blood bank records for previously identified antibodies before a patient is transfused. It is equally important to inform the patient that he or she has such an antibody and to provide a wallet card that notes the specificity in case the patient is transfused elsewhere. The decline in antibody reactivity and the difficulty in detecting Kidd antibodies are reasons why they are a common cause of HTRs, especially of the delayed type. Although

intravascular hemolysis has been noted in severe reactions, coated RBCs more often are removed extravascularly. The rate of clearance of incompatible RBCs can vary but is usually rapid. Contrary to their hemolytic reputation in transfusion, most Kidd antibodies are only rarely associated with severe cases of HDFN.42

Biochemistry Advanced Concepts Heaton and McLoughlin43 reported in 1982 that Jk(a–b–) RBCs resist lysis in 2M urea, a solution commonly used to lyse RBCs in a sample before it is used in some automated platelet-counting instruments. Urea crosses the RBC membrane, causing an osmotic imbalance and an influx of water, which rapidly lyses normal cells. With Jk(a+) or Jk(b+) RBCs, lysis in 2M urea occurs within 1 minute; with Jk(a–b–) cells, lysis is delayed by 30 minutes.7 The predicted Kidd glycoprotein has 389 amino acids with 10 membrane-spanning domains and two N-glycosylation sites, one of which is extracellular on the third extracellular loop (Fig. 8–10). The glycoprotein is a urea transporter. Genetics The Jk locus is on chromosome 18 at position 18q12.3. The gene SLC14A1 (for solute carrier family 14, member 1) is a member of the urea transporter gene family. The gene is organized into 11 exons. The Jka/Jkb polymorphism is associated with an amino acid substitution at position 280, predicted to be located on the fourth extracellular loop of the glycoprotein. Molecular studies have demonstrated the silent Jk allele can arise from mutations in both the Jka and Jkb alleles. Jka and Jkb are inherited as codominant alleles.

Jk(a–b–) Phenotype and the Recessive Allele, Jk People with the null Jk(a–b–) phenotype lack Jka, Jkb, and the common antigen Jk3. Although very rare, the Jk(a–b–) phenotype is most abundant among Polynesians, and it has also been identified in Filipinos, Indonesians, Chinese, and Japanese.1 The null phenotype has also been reported in several European families (Finnish, French, Swiss, and English) and in the Mato Grosso Indians of Brazil. The delayed lysis

Jka/Jkb

NH2

COOH

Figure 8–10. Proposed structure for Kidd protein. One of two proposed N-glycans is extracellular and is located on the third extracellular loop; the Jka/Jkb polymorphism is located on the fourth extracellular loop.

2682_Ch08_172-215 22/05/12 11:44 AM Page 199

Chapter 8 Blood Group Terminology and the Other Blood Groups

of Jk(a–b–) RBCs in 2M urea has proved an easy way to screen families and populations for this rare phenotype. No clinical abnormalities have been associated with the Jk(a–b–) phenotype to date. Several unrelated Jk(a–b–) individuals had normal blood urea nitrogen, creatinine, and serum electrolytes, but studies on two individuals with this phenotype showed a marked defect in their ability to concentrate urine. Family studies show that most Jk(a–b–) nulls are homozygous for the rare “silent” allele Jk. Parents of JkJk offspring and children of JkJk parents type Jk(a+b–) or Jk(a–b+) but never Jk(a+b+), because they are genetically JkaJk or JkbJk. Their RBCs also demonstrate a single dose of Jka or Jkb antigen in titration studies.

Jk(a–b–) Phenotype and the Dominant In(Jk) Allele Another genetic explanation for the Jk(a–b–) phenotype is association with a dominant gene called In(Jk), for “inhibitor,” that shows a dominant pattern of inheritance within a Japanese family analogous to the inhibitor gene responsible for the dominant type Lu(a–b–) phenotype in the Lutheran blood group system.7,9 Dominant type Jk(a–b–) RBCs adsorb and elute anti-Jk3 and anti-Jka or anti-Jkb (depending on which genes were inherited), indicating that the antigens are expressed but only very weakly. Individuals with the dominant type Jk(a–b–) phenotype do not make anti-Jk3. Family studies show that the In(Jk) gene does not reside at the Jk locus. The molecular basis is unknown.

Anti-Jk3 Alloanti-Jk3 is an IgG antiglobulin-reactive antibody that looks like an inseparable anti-JkaJkb. Because panel cells are Jk(a+) or Jk(b+), anti-Jk3 reacts with all RBCs tested except the autocontrol. Most blood banks do not have the rare cells needed to confirm anti-Jk3; however, they can easily determine its most probable specificity by means of antigen typing. The individual making the antibody will type Jk(a–b–). Like other Kidd antibodies, anti-Jk3 reacts optimally by an antiglobulin test, and the reactivity is enhanced with enzyme pretreatment of the RBCs. Anti-Jk3 has been associated with severe immediate and delayed HTRs and with mild HDFN. Compatible units are best found by typing siblings or searching the rare donor files.

Autoantibodies Autoantibodies with Kidd specificity (anti-Jka, anti-Jkb, and anti-Jk3) are rare, but they have been associated with autoimmune hemolytic anemia.1 As with other blood groups, Kidd autoantibodies may have mimicking specificity or may be associated with depressed antigen expression.

The Lutheran (005) System In 1945, anti-Lua was found (and described in detail a year later) in the serum of a patient with lupus erythematosus, following the transfusion of a unit of blood carrying the corresponding low-prevalence antigen.44 (This patient also

199

made anti-c, anti-N, the first example of anti-CW, and antiLevay, now known as Kpc!) The new antibody was named Lutheran for the donor; the donor’s last name was Lutteran but the donor blood sample was incorrectly labeled.2 In 1956, Cutbush and Chanarin45 described anti-Lub, which defined the antithetical partner to Lua. The blood group system appeared complete until 1961, when Crawford and colleagues46 described the first Lu(a–b–) phenotype. Unlike most null phenotypes at the time, this one demonstrated dominant inheritance. In 1963, the Lu(a–b–) phenotype inherited as a recessive silent allele was described. Twenty antigens are part of the Lutheran system, numbered through Lu22; some antigens are also known by other common names. Two numbers (Lu10 and Lu15) are obsolete. Most of these antigens are high prevalence; four sets of antigens are antithetical. Many of the antigens were associated with the Lutheran system when their corresponding antibodies were nonreactive with the rare Lu(a–b–) RBCs. All are summarized in Table 8–19. The ISBT designation of the Lutheran blood group system is LU or 005.

Basic Concepts Blood bankers seldom deal with the serology of the Lutheran blood group system. The antigens are either high prevalence, so only a few people lack the antigen and can make an alloantibody, or very low prevalence, so that only a few people are ever exposed. Consequently, the antibodies are seen infrequently, and there are not much data on the clinical significance of Lutheran antibodies. Although the antigens have been detected on fetal RBCs as early as 10 to 12 weeks of gestation, they are poorly developed at birth. As a result, HDFN is rare and only mild.9 Lutheran antigens have not been detected on platelets, lymphocytes, monocytes, or granulocytes. However, Lutheran glycoprotein is widely distributed in tissues: brain, lung, pancreas, placenta, skeletal muscle, and hepatocytes (especially fetal hepatic epithelial cells).7 The presence of Lutheran glycoprotein on placental tissue may result in adsorption of maternal antibodies to Lutheran antigens, thus decreasing the likelihood of HDFN.9 Lutheran antigens are resistant to the enzymes ficin and papain and to glycine-acid EDTA treatment but are destroyed by treatment with the enzymes trypsin and α-chymotrypsin. Most Lutheran antibodies do not react with RBCs treated with the sulfhydryl reagents DTT and AET.

Lua and Lub Antigens Lua and Lub are antigens produced by allelic codominant genes. The prevalence of common phenotypes are listed in Table 8–20. Most individuals are Lu(b+); 8% of whites and 5% of blacks are Lu(a+).9 Lutheran antigen expression is variable from one individual to another. The number of Lub sites per RBC is low, estimated to be from 1,640 to 4,070 on Lu(a–b+) RBCs and from 850 to 1,820 on Lu(a+b+) RBCs.7

2682_Ch08_172-215 22/05/12 11:44 AM Page 200

200

PART II

Blood Groups and Serologic Testing

Table 8–19 Lutheran System Antigens CONVENTIONAL NAME

PREVALENCE (%)

YEAR DISCOVERED

COMMENTS

Lua

8 whites 5 blacks

1945

Antithetical to Lub

Lub

99.8

1956

Antithetical to Lua

Lu3

> 99.9

1963

Lu4

> 99.9

1971

Lu5

> 99.9

1972

Lu6

> 99.9

1972

Lu7

> 99.9

1972

Lu8

> 99.9

1972

Antithetical to Lu14

Lu9

2

1973

Antithetical to Lu6

Lu11

> 99.9

1974

Lu12

> 99.9

1973

Lu13

> 99.9

1983

Lu14

2.4

1977

Lu16

> 99.9

1980

Lu17

> 99.9

1979

Aua, Lu18

80 whites

1961

Antithetical to Aub

Aub, Lu19

50 whites

1989

Antithetical to Aua

Lu20

> 99.9

1992

Lu21

> 99.9

2002

Lu22

> 99.9

2009

Antithetical to Lu9

Antithetical to Lu8

LURC

Lu (a+b–)

0.15

Lu (a+b+)

7.5

Lu (a–b+)

92.35

encountered as an incompatible crossmatch or during an antibody workup for another specificity. Experienced technologists recognize Lutheran antibodies by their characteristic loose, mixed-field reactivity in a test tube. Examples of anti-Lua that react only at temperatures below 37°C are clinically insignificant. There are no documented cases of immediate HTRs; there are only rare and mild delayed HTRs due to anti-Lua.1

Lu (a–b–)

Very rare

Anti-Lub

Table 8–20 Prevalence of Common Lutheran Phenotypes PHENOTYPE

MOST POPULATIONS (%)

Anti-Lua Most examples of anti-Lua are IgM naturally occurring saline agglutinins that react better at room temperature than at 37°C. A few react at 37°C by indirect antiglobulin test. Some are capable of binding complement, but in vitro hemolysis has not been reported. Anti-Lua often goes undetected in routine testing because most reagent RBCs are Lu(a–). Anti-Lua is more likely

Although the first example of anti-Lub was a room-temperature agglutinin, and IgM and IgA antibodies have been noted, most examples of anti-Lub are IgG and reactive at 37°C at the antiglobulin phase. The antibody is made in response to pregnancy or transfusion. Alloanti-Lub reacts with all cells tested except the autocontrol, and reactions are often weaker with Lu(a+b+) RBCs and cord RBCs. Anti-Lub has been implicated with shortened survival of transfused cells and post-transfusion jaundice, but severe or acute hemolysis has not been reported.

2682_Ch08_172-215 22/05/12 11:44 AM Page 201

Chapter 8 Blood Group Terminology and the Other Blood Groups

Biochemistry

Lu and the Se gene (FUT2) was the first example of autosomal linkage described in humans.

Advanced Concepts The Lutheran antigens are located on a type 1 transmembrane protein. The protein exists in two forms as a result of alternative RNA splicing: the longer Lu glycoprotein and the shorter basal cell adhesion molecule (B-CAM). The longer 85-kD protein contains 597 amino acids with five extracellular domains, a hydrophobic transmembrane domain of 19 amino acids, and a cytoplasmic domain of 59 amino acids (Fig. 8–11). The smaller isoform (78 kD) is identical except for a shorter cytoplasmic domain of 59 amino acids. The external portion consists of five disulfide-bonded domains. The Lutheran glycoproteins belong to the immunoglobulin superfamily of proteins; the repeating extracellular domains are homologous to immunoglobulin variable or constant domains. The Lutheran proteins are multifunctional adhesion molecules that bind laminin, notably in sickle cell disease.47 The molecular basis for the four pairs of antithetical antigens and several of the high-prevalence antigens has been determined through the creation of Lutheran glycoprotein mutants and subsequent sequencing of the exons encoding the extracellular domains. For most of the antigens, expression was caused by a single nucleotide polymorphism, resulting in single amino acid changes on the protein level.48 Genetics The Lu gene is located on chromosome 19 at position 19q13.2, along with genes that govern expression of several blood group antigens (H, Se, Le, LW, Oka) . A linkage between

Lua/Lub Lu21 Lu5 Lu17 Lu12 Lu4 Lu8/Lu14 Lu16

201

NH2

V

V

V

V

Lu20 Lu6/Lu9

C

C

Lu7

C

C

Lu13 Aua/Aub

C

C

Lu

B-CAM

Figure 8–11. The two structures encoded by the Lu gene: the longer Lu glycoprotein and the shorter basal cell adhesion molecule (B-CAM). The five extracellular disulfide-bonded domains are homologous to immunoglobulin variable (V) or constant (C) domains.

Lu(a–b–) Phenotypes Three genetic explanations for the Lu(a–b–) phenotype have been described. These are summarized in Table 8–21. Dominant Type Lu(a–b–) The first Lu(a–b–) family study was reported by the propositus herself.46 Because the phenotype was seen in successive generations in 50% of her family members and others, and because null individuals passed normal Lutheran genes to their offspring, the expression of Lutheran was thought to be suppressed by a rare dominant regulator gene later called In(Lu) for “inhibitor of Lutheran.” Recently, mutations in the gene for Erythroid Krüppel-like Factor (EKLF), a transcription factor, were shown to be associated with the In(Lu) phenotype in 21 of 24 In(Lu) individuals studied.49 In all cases, the mutated EKLF allele occurred in the presence of a normal EKLF allele. The authors of this study concluded that the In(Lu) phenotypeis caused by inheritance of a lossof-function mutation on one allele of EKLF. Dominant-type Lu(a–b–) RBCs carry trace amounts of Lutheran antigens as shown by adsorption-elution studies. For example, the RBCs of a person with the dominant type Lu(a–b–) who inherited two normal Lub genes will type Lu(a–b–) with routine methods but will adsorb and elute anti-Lub. Because individuals with the dominant type Lu(a–b–) RBCs have normal Lutheran antigens, they do not make anti-Lu3. In addition to reduced expression of Lutheran antigens, dominant type Lu(a–b–) RBCs also can have reduced expression of CD44 and a weak expression of P1, i, AnWj, MER2, and Inb blood group antigens. Recessive Type Lu(a–b–) In some families, the Lu(a–b–) phenotype demonstrates recessive inheritance, the result of having two rare silent alleles LuLu at the Lutheran locus. The parents and offspring of these nulls may type Lu(a–b–), but dosage studies and titers show them to carry a single dose of Lub. Unlike the dominant type, people with recessive Lu(a–b–) RBCs truly lack all Lutheran antigens (i.e., they have the null phenotype) and can make an inseparable anti-Luab called anti-Lu3. They also have normal antigen expression of P1, i, and the other antigens that are weakened with the dominant type. This distinction emphasizes the importance of testing an antibody against recessive Lu(a–b–) RBCs before defining the specificity phenotypically related to Lutheran. Different inactivating mutations were recently reported for three individuals with the recessive Lu(a–b–) type.50 In all three individuals the mutations would result in a truncated glycoprotein that would not be integrated in the RBC surface membrane. Recessive X-Linked Inhibitor Type An Lu(a–b–) phenotype in a large Australian family did not fit either the dominant or recessive inheritance patterns. All

2682_Ch08_172-215 22/05/12 11:44 AM Page 202

202

PART II

Blood Groups and Serologic Testing

Table 8–21 Summary of Lu(a–b–) Phenotypes MODE OF INHERITANCE

GENE RESPONSIBLE

Lu ANTIGENS

OTHER RBC ANTIGENS AFFECTED

MAKE ANTI-Lu3?

Dominant

EKLF49 Not at Lu locus

Extremely weak

Reduced P1, i, Inb, AnWj, MER2, CD44

No

Recessive

Lu

None

Not affected

Yes

X-linked

XS2

Extremely weak

Not affected

No

Lu(a–b–) family members were male and carried trace amounts of Lub detected by adsorption-elution. The pattern of inheritance suggested an X-borne inhibitor to Lutheran. The researchers proposed calling the locus XS, XS1 being the common allele and XS2 the rare inhibitor that suppresses in a hemizygous state. There have been no other families reported with this rare X-linked Lu(a–b–) phenotype.9

Anti-Lu3 Anti-Lu3 is a rare antibody that reacts with all RBCs except Lu(a–b–) RBCs. The antibody looks like inseparable antiLuab and recognizes a common antigen, Lu3, that is present whenever Lua or Lub is present (much like the Jk3 association with Jka and Jkb). Anti-Lu3 is usually antiglobulinreactive. This antibody is made only by individuals with the recessive type of Lu(a–b–).

The Diego (010) System The Diego system is composed of 22 antigens: three sets of independent pairs of antithetical antigens—Dia/Dib, Wra/Wrb, and Wu/DISK—and 17 low-prevalence antigens.3,7 The system was named after the first antibody maker in a Venezuelan family during an investigation of HDFN. The Diego system is designated DI and number 010 by the ISBT. The Diego antigens are carried on band 3, a major integral RBC membrane glycoprotein with about 1 million copies per RBC. Band 3 is also known as the red cell anion exchanger (AE1) or solute carrier family-4. anion exchanger, member 1 (SLC4A1). The protein crosses the membrane multiple times, and both the amino- and carboxyl-terminal domains are in the cytoplasm. A large N-glycan on the fourth external loop carries over half the RBC A, B, H, and I blood group antigens. The long amino-terminal domain of band 3 interacts with ankyrin and protein 4.2 of the membrane skeleton. The gene encoding band 3 and the Diego antigens, SLC4A1, consists of 20 exons and is located at chromosome 17q21-q22. Reported in 1955, anti-Dia had caused HDFN in a Venezuelan baby. Anti-Dib was described 2 years later. Dia is rare in most populations but is polymorphic in people of Mongoloid ancestry. In South American Indians, the prevalence of Dia can be as high as 54%.9 Dia is also present in the North and Central American native populations but is surprisingly rare in Canada and among the Alaskan Inuit.7 The prevalence of Dib is generally greater than 99% but is 96% in Native Americans. The Dia/Dib polymorphism is

located on the last (seventh) extracellular loop of the protein. The Di(a–b–) phenotype has not been reported. Wra, a low-prevalence antigen, and the antithetical, highprevalence Wrb are associated with an amino acid substitution on the fourth external loop, close to the insertion point of the protein into the RBC membrane. However, expression of Wrb requires the presence of both band 3 and a normal GPA of the MNS blood group system. GPA-deficient RBCs are Wr(a–b–).7 Localization of Dia and Dib antigens to band 3 enabled many low-prevalence antigens to be assigned to the Diego system: Wda, Rba, WARR, ELO, Wu, Bpa, Moa, Hga, Vga, Swa, BOW, NFLD, Jna, KREP, Tra, Fra, and Sw1. Diego antigens are expressed on RBCs of newborns. The antigens are resistant to treatment with ficin and papain, DTT, and glycine-acid EDTA, with the exception of Bpa, which is sensitive to papain.7,9 Diego system antibodies are sometimes IgM, but are usually IgG, reactive in the indirect antiglobulin test. Both anti-Dia and anti-Dib have caused HTRs and HDFN.7,9 Anti-Wra is a relatively common antibody in donors and patients; some are directly agglutinating, but most require the indirect antiglobulin test to be detected. Anti-Wra has caused severe HTRs. Only a few examples of alloanti-Wrb in individuals with Wr(a–b–) RBCs have been described, so information about clinical significance is insufficient. Autoanti-Wrb is relatively common in the serum of patients with warm autoimmune hemolytic anemia. Little or no data are available on the clinical significance of antibodies to the low-prevalence Diego antigens, with the exception of anti-ELO, which has caused severe HDFN.7

The Yt (011) System Two antigens make up the Yt system, which was named in 1956 for the first antibody maker and used the last letter “t” in the patient’s last name, which was Cartwright.51 Apparently “why T” became “Yt.”9 Yta is the high-prevalence antigen in all populations; Ytb is the low-prevalence antigen found in about 8% of whites and 21% to 26% of Israelis, but it is not found in Japanese.7,9 Three phenotypes are observed: the common Yt(a+b–) and Yt(a+b+) and the rare Yt(a–b+). The Yt(a–b–) phenotype has not been reported. The Yt system has the ISBT designation YT and system number 011. The Yt antigens are antithetical and represent an amino acid substitution on the glycosylphosphatidylinositol (GPI)linked RBC glycoprotein acetylcholinesterase (AChE). AChE is an important enzyme participating in neurotransmission,

2682_Ch08_172-215 22/05/12 11:44 AM Page 203

Chapter 8 Blood Group Terminology and the Other Blood Groups

but the function of RBC-bound AChE is not known. The gene is located at chromosome 7q22. Yt antigens are variably sensitive to ficin and papain, are sensitive to DTT, and are resistant to glycine-acid EDTA treatment. The antigens are developed at birth but are expressed more weakly on cord RBCs than on adult RBCs, and are absent from RBCs of people with paroxysmal nocturnal hemoglobinuria (PNH) III.7 Anti-Yta and anti-Ytb are IgG and are stimulated by pregnancy or transfusion. Anti-Yta is not an uncommon antibody, so it appears that Yta is reasonably immunogenic. However, Ytb appears to be a poor immunogen, as the antibody is rare. Yt antibodies have not caused HDFN. Some examples of anti-Yta have been shown to be clinically significant for transfusion while others have not.7

The Xg (012) System Anti-Xga was discovered in 1962 in the serum of a multiply transfused man. The antibody detected an antigen with a higher prevalence in females than in males. Family studies were used to confirm the antigen Xga expression was controlled by an X-linked gene. The antigen was named after the X chromosome and g for “Grand Rapids,” where the patient was treated.9 The Xg system is designated by the symbol XG and number 012. There are two antigens in the Xg system: Xga and CD99. CD99 is also known as 12E7 and MIC2. The gene encoding Xga is located on the X chromosome at Xp22.3. The gene responsible for CD99, MIC2, is located at Xp22.2. CD99 became part of the Xg system because the MIC2 and XG genes are adjacent and homologous. Xga has a phenotypic relationship to CD99: all Xg(a+) individuals have a high expression of CD99 on their RBCs and all Xg(a–) females have a low expression of CD99, but 68% of Xg(a–) males have a high expression and 32% have a low expression of CD99.7 Both Xga and CD99 escape X chromosome inactivation. The Xg glycoprotein crosses the RBC membrane once, with the amino terminus directed externally. There are approximately 9,000 copies of Xga per RBC.9 The prevalence of Xga is 66% in males and 89% in females. Because males have only one X chromosome, Xg(a+) males are hemizygotes. Females, having two X chromosomes, can be homozygotes or heterozygotes. However, homozygosity for the gene does not directly correlate to RBC antigen strength.52 Cord RBCs express Xga weakly. Weak expression of Xga is seen on RBCs from some adult females, but weak expression on RBCs from adult males is rare.9 The antigen is sensitive to ficin and papain but resistant to DTT treatment. Anti-Xga is usually IgG; some examples are naturally occurring. Anti-Xga has not been implicated in HDFN or as a cause of HTRs. Two CD99– Japanese individuals have been found with alloanti-CD99.

The Scianna (013) System The Scianna blood group system, ISBT symbol SC and number 013, currently consists of seven antigens. The system is

203

named after the first antibody maker. In 1962, a new highprevalence antigen was named Sm; 1 year later, a new lowprevalence antigen, Bua was found. After it was confirmed that these two antigens were antithetical, the Scianna blood group system was established in 1974 and the two antigens were renamed Sc1 and Sc2, respectively. The prevalence of Sc2 in Northern Europeans is 1% but is higher in the Mennonite population. In 1980, an individual in the Marshall Islands in the South Pacific was found with the Sc:–1,–2 phenotype. He had made an antibody to an unknown high-prevalence antibody. The antibody was named anti-Sc3; separable anti-Sc1 and antiSc2 were not identified. The very rare Sc:–1,–2,–3 phenotype is the Scianna null type. Three examples of anti-Sc3, nonreactive with Sc:–1,–2, were found to be incompatible with the RBCs of the other anti-Sc3 makers, indicating the existence of additional high-prevalence antigens.53 The SC gene is located on chromosome 1 at 1p34. The product of the gene is a protein called erythroid membraneassociated protein (ERMAP), which is an RBC adhesion protein. Once location of Scianna to ERMAP was made, other antigens were assigned to the system. The low-prevalence antigen Rd became Sc4. Sc5 (STAR), Sc6 (SCER), and Sc7 (SCAN) are all high-prevalence antigens.54 The Scianna antigens are resistant to ficin and papain but are slightly weakened by DTT treatment. The antigens are expressed on cord RBCs. Alloantibodies to Scianna antigens are rare and little is known about their clinical significance. They are usually IgG and reactive in the antiglobulin test. None have been reported to cause a severe HTR. Only mild HDFN has been reported, except for one severe case for anti-Sc4, for which the baby required exchange transfusion. Autoantibodies to Sc1 and Sc3 have been reported.

The Dombrock (014) System The Dombrock blood group system, designated by the ISBT with the symbol DO and number 014, was named for the first antibody maker, Mrs. Dombrock, found in 1965. Anti-Dob, which recognizes the antithetical antigen, was identified in 1973. The prevalence of the three resulting phenotypes, Do(a+b–), Do(a+b+), and Do(a–b+), varies in different populations. In whites, they are 18%, 49%, and 33%, respectively. The high-prevalence antigens Gya and Hy were both described in 1967. RBCs from whites who are Gy(a–) were found to be Hy–, but Hy– RBCs from blacks were weakly Gy(a+). The high-prevalence antigen Joa was described in 1972, and the phenotypic relationship to Gya and Hy was later shown: Gy(a–) RBCs or Hy– RBCs are also Jo(a–). In 1995, it was reported that Gy(a–) RBCs were also Do(a–b–).55 The Gy(a–) phenotype is the Dombrock null. Two additional high-prevalence antigens, DOYA and DOMR, were recently added to the system.3 The Hy– and Jo(a–) phenotypes are not found in whites and are rare in blacks. The Dombrock antigens are carried on a mono-ADPribosyltransferase 4 (ART4) attached to the RBC membrane by a GPI anchor. The gene encoding the Dombrock glycoprotein is located at chromosome 12p12.3.

2682_Ch08_172-215 22/05/12 11:44 AM Page 204

204

PART II

Blood Groups and Serologic Testing

The Dombrock antigens are resistant to ficin, papain, and glycine-acid EDTA, and are sensitive to 0.2 M DTT treatment. The antigens are present on cord RBCs, but are absent from PNH III RBCs. The Doa and Dob antigens are considered to be poor immunogens and the antibodies are rarely found as single specificities; Gya, however, is highly immunogenic.9 Anti-Doa and anti-Dob have caused delayed HTRs but no clinical HDFN. The Dombrock antibodies are usually IgG, reacting optimally with enzyme-treated RBCs. These antibodies are usually weakly reactive and disappear, both factors making them difficult to identify.

The Colton (015) System The Colton blood group system, ISBT symbol CO and number 015, consists of four antigens. The system was named in 1967 for the first antibody maker; it should have been named Calton, but the handwriting on the tube was misread!9 The high- and low-prevalence antithetical antigens are Coa and Cob, respectively. The Cob antigen is present in about 10% of most populations.9 The third antigen, Co3, is present on all RBCs except those of the very rare Co(a–b–) phenotype. Co4, a high-prevalence antigen, has been identified on RBCs from two individuals with the Co(a–b–) phenotype.3 The Colton antigens are carried on an integral membrane protein, aquaporin 1 (AQP1), which accounts for 80% of water readsorption in the kidneys.9 The glycoprotein crosses the RBC membrane multiple times. The gene (AQP1) is located at chromosome 7p14. The Colton antigens are expressed on RBCs of newborns and are resistant to treatment with ficin and papain, chloroquine, and DTT. Antibodies are usually IgG and are enhanced with enzymetreated RBCs. Anti-Coa is often seen as a single specificity and has been reported to cause HTRs and HDFN.56 Anti-Cob appears more often with other specificities but has also caused HTRs and mild HDFN.9 Anti-Co3, which reacts with all Co(a+) and Co(b+) RBCs, has been reported to cause severe HDFN.1

The Landsteiner-Wiener (016) System The Landsteiner-Wiener blood group system, ISBT symbol LW and number 016, had its origins along with the discovery of the D antigen of the Rh blood group system. In 1940,

Landsteiner and Wiener reported that an antibody produced in rabbits (and later, guinea pigs) after injection with RBCs of rhesus monkeys reacted with 85% of human RBCs.57 This antibody was called anti-Rh for anti-rhesus. The reactivity of anti-Rh was similar to the human antibody reported by Levine and Stetson in 1939 in a woman who delivered a stillborn infant and had a transfusion reaction to the blood donated by her husband.58 Both sera identified the same population of Rh+ and Rh– RBCs. The two antibodies were later shown to be different in several studies; in the 1960s, the human anti-Rh was renamed anti-D (but called anti-Rho by some workers) and the rabbit anti-Rh was called anti-LW in honor of Landsteiner and Wiener. Examples of human anti-LW were subsequently described. There are three LW antigens: LWa, LWab, and LWb. The first two, LWa and LWab, are common, high-prevalence antigens, and LWb is of low prevalence, found in less than 1% of most Europeans but in 6% of Finns.9 LWab was originally defined by the antibody made by an individual with an inherited LW(a–b–) phenotype. Terminology for LW antigens has evolved as more information became available. The ISBT has used LW5, LW6, and LW7 as the antigen numbers for LWa, LWab, and LWb, respectively, to prevent confusion with obsolete terminology that used LW1-LW4 to designate phenotypes. The null phenotype is LW(a–b–); in one individual who made anti-LWab (Mrs. Big), this phenotype resulted from a 10 base pair deletion in exon 1 of an LWa gene, which introduced a premature stop codon. Rhnull RBCs also type LW(a–b–) and are considered to be the only true LW– RBCs because they fail to elicit the formation of anti-LW in animals, whereas injection of Mrs. Big’s LW(a–b–) RBCs into guinea pigs caused the formation of anti-LW. The LW phenotypes are shown in Table 8–22. As was shown by the similarity in reactivity of the original animal anti-Rh and the human anti-Rh (later called anti-D), there is a phenotypic relationship between the D antigen and anti-LW. Anti-LW usually reacts strongly with D+ RBCs, weakly (and sometimes not at all) with D– RBCs from adults, and not at all with Rhnull RBCs. A weak anti-LW may react only with D+ RBCs and may appear to be anti-D unless enhancement techniques are used. This is because there are more LW antigen sites on D+ RBCs from adults than on D– RBCs.9 However, anti-LW reacts equally well with cord RBCs regardless of their D type. Distinguishing anti-LW

Table 8–22 LW Phenotypes PHENOTYPE

REACTIVITY WITH

PREVALENCE

Anti-LWa

Anti-LWb

Anti-LWab

LW(a+b–)

+

LW(a+b+)

+

LW(a–b+)

Most Europeans

Finns

+

97%

93.9%

+

+

3%

6%

+

+

Rare

0.1%

LW(a–b–) Big

LW(a–b–) Rhnull

2682_Ch08_172-215 22/05/12 11:44 AM Page 205

Chapter 8 Blood Group Terminology and the Other Blood Groups

from anti-D is most easily accomplished by testing DTTtreated D+ RBCs: the D antigen is not denatured by DTT, so anti-D would still be detected; however, LW antigen is destroyed by DTT, so anti-LW would no longer react. LW antigens are resistant to treatment of RBCs with enzymes and glycine-acid EDTA. The structure that carries the LW antigens is a glycoprotein known as intracellular adhesion molecule 4 (ICAM-4), a member of the immunoglobulin superfamily. The LW glycoprotein is part of the band 3/Rh macrocomplex59; Rhnull RBCs lack the LW glycoprotein. The LW gene is located on chromosome 19 at 19p13.3. LW antigens may be depressed during pregnancy and in some diseases, such as lymphoma and leukemia.9 AutoantiLW made by these patients can appear to be an alloantibody; as the antigen strength returns the antibody diminishes. Autoanti-LW is also common in serum from patients with warm autoimmune hemolytic anemia. No anti-LW has been shown to cause serious HDFN or transfusion reactions. Many patients with anti-LW have successfully been transfused with D– RBCs. Only two examples of alloanti-LWab have been described, the antibodies of the only two known propositi with an inherited LW(a–b–) phenotype.7

The Chido/Rodgers (017) System The Chido/Rodgers blood group system, designated by the ISBT with symbol CH/RG and number 017, was named after the first two antibody producers, Ch for Chido and Rg for Rodgers. These two antibodies were described in 1967 and 1976, respectively. Serologically, they were both characterized as nebulous because antigen strength on different samples of RBCs was variable.1 It was also appreciated that both anti-Ch and anti-Rg could be neutralized by plasma. Ch and Rg antigens are not intrinsic to the RBC membrane. Rather, they are on the fourth component of complement (C4), and are adsorbed onto RBCs from plasma.1 The C4 glycoprotein has two isoforms: C4B carries the Ch antigens and C4A expresses Rg antigens. Genes at two closely linked loci located at chromosome 6p21.3 encode these isoforms. The Chido/Rodgers system consists of nine antigens: Ch1 to Ch6, Rg1, and Rg2 are all high prevalence; WH has a prevalence of about 15%.9 Differentiation of the determinants is not made for routine serology. Ch is present in 96% to 98% of most populations.1,9 Rg is present in 97% to 98% of most populations.1,9 The antigens are destroyed by ficin and papain but are resistant to treatment with DTT and glycine-acid EDTA.9 Anti-Ch and anti-Rg are usually IgG and react weakly, often to moderate or high titration endpoints. Neutralization of anti-Ch and anti-Rg with pooled plasma is often used as part of the identification of these antibodies in a patient’s serum. Anti-Ch and anti-Rg are clinically insignificant for transfusion.1

The Gerbich (020) System The Gerbich blood group system was named in 1960 after Mrs. Gerbich, the first antibody producer. Gerbich became

205

a system in 1990, designated by the ISBT as GE and number 020. There are currently six high-prevalence Gerbich antigens (Ge2, Ge3, Ge4, GEPL, GEAT, and GETI) and five lowprevalence antigens (Wb, Lsa, Ana, Dha, and GEIS). The antigens are carried on sialoglycoprotein structures GPC and GPD. The glycoproteins help to maintain the RBC membrane integrity through interaction with protein band 4.1, and because they are rich in sialic acid, they contribute to the net negative charge of the RBC membrane (as do GPA and GPB of the MNS system). There are about 135,000 copies of GPC and 50,000 copies of GPD per RBC.9 GPC and GPD are both encoded by the GYPC gene, located on chromosome 2 at 2q14.3. There are three Gerbich-negative phenotypes in which the RBCs lack one or more of the high-prevalence antigens: Ge:–2,3,4 (Yus type), Ge:–2,–3,4 (Gerbich type), and Ge:–2,–3,–4 (Leach type). The Leach type is the Gerbich null phenotype. These are summarized in Table 8–23. Outside of Papua, New Guinea, the Gerbich-negative phenotypes are very rare, but they have been found in diverse populations. The Yus phenotype has been found in Mexicans, Israelis, and others but has not been found in Papua, New Guinea and other Melanesians.9 The Gerbich phenotype is polymorphic in certain areas of Papua, New Guinea and has also been found among Europeans, Africans, Native Americans, Japanese, and Polynesians.9 Gerbich antigens are expressed at birth. RBCs of the Gerbich or Leach phenotypes have weak expression of Kell blood group antigens, and some anti-Vel fail to react with Ge:–2,–3,4 RBCs.9 Gerbich antigens are resistant to treatment with DTT and glycine-acid EDTA; Ge2 and Ge4 are ficin and papain sensitive, but Ge3 is ficin resistant. Some Gerbich antibodies may be IgM, but most are IgG. Gerbich antibodies are sometimes clinically significant for transfusion and sometimes not. Gerbich antibodies can be eluted from DAT+ cord bloods, but only three cases of serious HDFN due to anti-Ge3 have been reported, and two were children of the same mother.60,61 In these cases, the severe anemia was late onset, after birth, associated with inhibition of erythroid cell growth; in one case there was also early onset of hemolysis. Anti-Ge2 is the most common of the Gerbich antibodies.7 It is the antibody made by the Ge:–2,3,4 phenotype individuals, but it is also the more common antibody made by the Ge:–2,–3,4 phenotype and Ge:–2,–3,–4 phenotype individuals. Anti-Ge3 is less frequently made by the Ge:–2,–3,4 and Ge:–2,–3,–4 phenotype individuals. Anti-Ge4 is a very rare antibody.

Table 8–23 Gerbich-Negative Phenotypes PHENOTYPE

TYPE

ANTIBODY

Ge: –2, 3, 4

Yus

Anti-Ge2

Ge: –2, –3, 4

Gerbich

Anti-Ge2 or anti-Ge3

Ge: –2, –3, –4

Leach type

Anti-Ge2 or anti-Ge3

2682_Ch08_172-215 22/05/12 11:44 AM Page 206

206

PART II

Blood Groups and Serologic Testing

The Cromer (021) System In 1965, an antibody was found in a black prenatal patient, Mrs. Cromer, that reacted with all RBCs except her own and two siblings. It was originally thought her antibody recognized an antigen antithetical to Goa of the Rh blood group system. The antibody was named anti-Cra in 1975.7,9 The antigens of the Cromer system are carried on decay accelerating factor (DAF, CD55), a complement regulatory protein. The CD55 gene is located at chromosome 1q32. The glycoprotein encoded by the gene is attached to the RBC membrane through a GPI linkage. PNH III RBCs are deficient in DAF so they also lack Cromer antigens. The Cromer system has 16 antigens: 13 high-prevalence antigens and 3 low-prevalence antigens.62,63 All these antigens are absent from Inab phenotype RBCs, the Cromer null phenotype, which is very rare. The Cr(a–) phenotype is typically found in blacks and is not found in whites. Three Cromer antigens, Tca, Tcb, and Tcc, are antithetical; Tca is the high-prevalence antigen and the other two are low prevalence. The Dra antigen is of high prevalence; Dr(a–) RBCs have weakened expression of all other highprevalence Cromer antigens due to a markedly reduced copy number of DAF. Cromer system antigens are resistant to treatment with ficin and papain but are destroyed by α-chymotrypsin, which is used to distinguish specificities in this system from other blood group antibodies. Cromer antigens are weakened with DTT treatment and are resistant to glycine-acid EDTA. Antibodies in the Cromer system are usually IgG, but do not cause HDFN. DAF is strongly expressed on placental tissue and will adsorb Cromer antibodies.9,63 Anti-Cra and anti-Tca have been implicated in HTRs, but other examples of these specificities have not caused clinical reactions after transfusion of incompatible units.62 Anti-IFC is the antibody made by individuals with the Cromer null Inab phenotype.

The Knops (022) System There are nine antigens in the Knops blood group system, designated by the ISBT as KN and number 022. The system was established when the antigens were shown to be located on complement receptor 1 (CR1) and was named after Mrs. Knops, the first antibody maker. The gene is located at chromosome 1q32. With the exception of the low-prevalence antigens Knb and McCb, the Knops antigens have a prevalence of more than 90% in most populations; however, ethnic differences exist. Sla is present on RBCs of only about 60% of African Americans. Among West Africans, Sla has a prevalence of 30% to 38%, and KCAM has a prevalence of only 20%.64 The antithetical pairs of antigens are Kna and Knb, McCa and McCb, and Sla and Vil. Knops antigens are weakly expressed on cord RBCs and weaken upon storage of adult RBCs (e.g., older units of blood). The antigens are weakened by treatment with ficin and papain and are destroyed by DTT; the antigens are resistant to glycine-acid EDTA.9 Serologically, these antigens have been grouped together because their corresponding antibodies demonstrate variable

reactions, are not neutralized by pooled normal serum (unlike anti-Ch and anti-Rg), and are difficult to adsorb and elute.64 Antibody reactivity is enhanced with longer incubation (e.g., 1 hour, at 37°C). Weak and variable reactivity is due to variable expression of CR1 on different samples of RBCs. The “Helgeson phenotype” represents the serologic null phenotype for the Knops blood group; these RBCs type Kn(a–b–), McC(a–), Sl(a–), and Yk(a–) because of the low copy number of CR1, but they are not truly devoid of Knops antigens.9,64 The antibodies are usually IgG, reactive in the antiglobulin test, but are clinically insignificant for both transfusion and HDFN. Of the Knops antibodies, anti-Kna is frequently found in multiply transfused individuals and multispecific sera; anti-Sla is more frequently found in blacks. CR1 binds the complement component fragments C3b and C4b and processes immune complexes for transportation to the liver and spleen and subsequent clearance from the circulation.7,64 CR1 has also been identified as a receptor for several pathogenic organisms.

The Indian (023) System The Indian blood group system was named because the first In(a+) individuals were from India. There are now four antigens in the system, designated IN and number 023 by the ISBT. The antigen Ina was reported in 1973 and is present on RBCs of 4% of Indians, 11% of Iranians, and 12% of Arabs.9 Inb is the antithetical high-prevalence antigen. These and two other high-prevalence antigens are located on CD44, an adhesion molecule. The gene encoding CD44 is located at chromosome 11p13. The extremely rare In(a–b–) phenotype has been found in only one individual who presented with congenital dyserythropoietic anemia and whose RBCs also typed Co(a–b–).65 CD44 is reduced on RBCs of dominant type Lu(a–b–) individuals. Ina and Inb are weakly expressed on cord RBCs and are sensitive to treatment with ficin, papain, and DTT but are resistant to glycine-acid EDTA.9 Antibodies are usually IgG and reactive in the antiglobulin test and they do not bind complement. Positive DATs but no clinical HDFN have been reported for anti-Ina and anti-Inb; decreased cell survival with anti-Ina and an immediate HTR due to anti-Inb have been reported.9

The Ok (024) System Currently, there are three high-prevalence antigens in the Ok system, designated by the ISBT symbol OK and number 024. Anti-Oka was identified in 1979 and was named after the antibody maker, Mrs. Kobutso. Because Ko was already in use, the first two letters were switched to Ok.2 Her parents were cousins from a small Japanese island. Two of three siblings of the proposita were also Ok(a–).7 RBCs from 400 individuals from the same island were all Ok(a+).1 Two additional antigens, OKGV and OKVM, were recently added to the system. The OK antigens are carried on CD147, a member of the immunoglobulin superfamily that mainly functions as receptors and adhesion molecules. The gene locus is at chromosome 19p13.3.

2682_Ch08_172-215 22/05/12 11:44 AM Page 207

Chapter 8 Blood Group Terminology and the Other Blood Groups

Oka is well developed on RBCs from newborns and is resistant to treatment with ficin and papain, DTT, and glycine-acid EDTA.9 The original anti-Oka was IgG, reactive in the antiglobulin test. At least one other example of the antibody has been found. The antibody caused reduced survival of 51Cr-labeled Ok(a+) RBCs injected into the original antibody maker.1 Anti-Oka has not been reported to cause HDFN.

The Raph (025) System The only antigen in the Raph system is MER2, which was originally defined by two monoclonal antibodies; it has since been recognized by human polyclonal antibodies. The antigen name is derived from monoclonal, and Eleanor Roosevelt, the laboratory where the antibody was produced. When MER2 was raised to system status, the system was named Raph for the first patient to make the alloanti-MER2. MER2 is encoded by a gene located at chromosome 11p15. Three examples of alloanti-MER2 were found in Jews originating from India and living in Israel; two were related. All three had end-stage renal disease. A fourth example of anti-MER2 was found in a healthy Turkish blood donor. Blood samples from these four individuals were studied. It was shown that MER2 is located on CD151, a tetraspanin, which appears to be essential for the assembly of basement membranes in the kidney and skin.66 The polymorphism identified by the monoclonal antibodies indicated that 8% of the English blood donor population is MER2–. Subsequent studies suggest the antigen-negative status represents the low end of antigen expression on RBCs.66 MER2 is abundant on platelets and is expressed on erythroid precursors of individuals with either MER2+ or MER2– RBCs. MER2 expression decreases over time with increasing maturation of erythroid cells.66 It has been suggested that most people whose RBCs type MER2– have MER2 expressed on other cells and tissues and will not make anti-MER2, and those individuals who have made alloantiMER2 are true MER2–. Those individuals who have made anti-MER2 showed mutations in CD151. In the patients with renal disease, a truncated CD151 protein would be predicted, but in patients without renal disease, mutations would result in an altered CD151 that appears to be present and functional at the cell surface.66,67 The antigen is resistant to treatment with ficin and papain but is sensitive to treatment with trypsin, α-chymotrypsin, pronase, and AET. Little is known about the clinical significance of antiMER2, but one patient with the antibody showed signs of a transfusion reaction after transfusion with 3 units. As 8% of the population is expected to be MER2–, it would be prudent to transfuse with crossmatch compatible units.67

The John Milton Hagen (026) System JMH is a high-prevalence antigen. Numerous examples of anti-JMH have been seen, especially in patients 50 years and older. In 1978, a large number of samples with this antibody were characterized and the antibody was named anti-JMH

207

for the first antibody maker, John Milton Hagen. The system (ISBT symbol JMH and number 026) was established after it was shown that the JMH protein is the GPI-linked glycoprotein CD108 and the gene SEMA7A was cloned. The gene is located at chromosome 15q24.1. Five other antigens were recently added to the system, JMH2 through JMH6; these are JMH variants associated with amino acid substitutions in the protein.68 JMH1 represents the antigen recognized by antibodies made by individuals lacking the JMH protein. Most examples of anti-JMH are not found in patients who lack the JMH protein or who have one of the variant JMH phenotypes. Rather, the patient’s JMH– status is acquired and can be transient.1 It is widely accepted that JMH levels decline during the later years of life, sometimes to the point of not being detected serologically.1 Once JMH expression is reduced, anti-JMH can be made. In some cases with anti-JMH, the DAT is positive and some JMH is detected on the patient’s RBCs. This autoanti-JMH with a positive DAT has never been associated with autoimmune RBC destruction.1 JMH is weakly expressed on cord RBCs and is destroyed by treating RBCs with ficin and papain, and DTT; the antigen is resistant to treatment with glycine-acid EDTA.9 Anti-JMH is usually IgG (predominantly IgG4 in acquired JMH-negative people).9 The antibodies are often high titer but weakly reactive, even when tested without dilution, and they are not neutralized with pooled plasma. JMH antibodies are generally considered clinically insignificant. Rare examples of alloanti-JMH in individuals whose RBCs express variant forms of CD108 may be clinically significant.1

The Gill (029) System Anti-GIL was first identified in 1980, but the antigen was not raised to system status until 2002 when it was shown that GIL is genetically discrete from all other blood group systems. The ISBT Gill system symbol is GIL and number 029. There is only one antigen, GIL. This antigen is found on the glycerol transporter aquaporin 3 (AQP3), a member of the major intrinsic protein family of water channels. AQP3 is located at chromosome 9p13. The GILnull phenotype results from a frameshift and a premature stop codon. Reactivity with anti-GIL is enhanced with ficin and papain treatment of RBCs; the antigen is resistant to DTT and glycine-acid EDTA treatment. RBCs of two babies born to mothers with anti-GIL have had a positive DAT but no clinical HDFN.7 One example of anti-GIL was found following a hemolytic transfusion reaction.

The RH-Associated Glycoprotein (030) System Rh-associated glycoprotein is the newest blood group system (IBST symbol RHAG and number 030).3 The Rhassociated glycoprotein (RhAG) does not have Rh blood

2682_Ch08_172-215 22/05/12 11:44 AM Page 208

208

PART II

Blood Groups and Serologic Testing

group antigens; however, its presence in a complex with the Rh proteins is essential for Rh antigen expression. Absence of RhAG due to inactivating mutations in RHAG results in the Rhnull phenotype; some missense mutations in RHAG result in the Rhmod phenotype.69 Unlike the RhD and RhCcEe proteins, RhAG is glycosylated on the first extracellular loop. RhAG is encoded by RHAG, located at chromosome 6p11-21. Two antigens have been definitively assigned to the RHAG system: Duclos (RHAG1), previously 901013 in the highprevalence series, and Ola (RHAG2), previously 700043 in the low-prevalence series. Two antigens, DSLK (for Ducloslike) and RHAG4, have been provisionally assigned to the system.

Miscellaneous Antigens Vel Vel, a high-prevalence antigen, is in the Vel collection, along with another high-prevalence antigen ABTI. Anti-Vel was first described in 1952 and was named after the first antibody maker. Anti-Vel is characterized by its ability to activate complement and cause in vitro and in vivo hemolysis. The antibody is most often IgG but can be IgM, and it has caused severe, immediate HTRs.1,7 Anti-Vel has also caused one case of severe HDFN in which the mother had previously been transfused.9 Vel antigen expression is weak on cord RBCs and can be variable on RBCs of different adult individuals. RBCs with weak expression of Vel can be mistyped as Vel–. This is one of the reasons why anti-Vel can be a difficult antibody to work with and identify. Reactivity with anti-Vel can be enhanced with enzyme-treated RBCs. The antigen is also resistant to glycine-acid EDTA and DTT treatment, though some examples of anti-Vel do not react with DTT-treated RBCs.70

cases of no to mild HDFN, the mothers had not been transfused.71 Some patients with anti-Jra have received Jr(a+) incompatible units for transfusion and have had no ill effect, but in other cases, incompatible transfusions have resulted in HTRs.72

Sda The Sda antigen is a high-prevalence antigen named for Sid, who was the head of the maintenance department at the Lister Institute in London. His RBCs had been used for many years as a panel donor, and they reacted strongly with examples of a new antibody. The soluble form of Sda is TammHorsfall glycoprotein found in urine. The antigen is not expressed on RBCs of newborns but is in their saliva, urine, and meconium. The strength of Sda on adult RBCs varies and is markedly reduced in pregnancy. The antigen is found on 91% of RBC samples, and Sda substance is found in 96% of urine samples. Only 4% of people are Sd(a–).9 Strong examples of Sda are noted as Sd(a++). Anti-Sda can naturally occur (i.e., without known stimulation by transfusion or pregnancy) in the sera of individuals who are Sd(a–). Anti-Sda is usually an IgM agglutinin that is reactive at room temperature, but it can be detected in the indirect antiglobulin test and does not react with cord RBCs. Reactivity is described as small, refractile (shiny) agglutinates in a sea of free RBCs. Because the soluble antigen is present in urine of Sd(a+) individuals, neutralization of the refractile agglutinates by urine is a technique used to identify anti-Sda. The Sda antigen is resistant to treatment with ficin, papain, DTT, and glycine-acid EDTA. Reactivity of the antibody is enhanced with enzyme-treated RBCs. Anti-Sda is generally considered clinically insignificant for transfusion, though there are two reports of transfusion reactions associated with the transfusion of Sd(a++) RBCs.

Applications to Routine Blood Banking Ata Anti-Ata was first described in 1967 in the serum of a black woman named Mrs. Augustine.1 Ata is a high-prevalence antigen, and all At(a–) individuals have been black. The antigen is fully developed at birth and is resistant to treatment with ficin and papain, DTT, and glycine-acid EDTA. The antibody is usually IgG, reactive in the antiglobulin test. Anti-Ata has caused severe HTRs and one reported mild case of HDFN.7,9

Jra Jra is a high-prevalence antigen in most populations; the Jr(a–) phenotype is found more commonly in Japanese. The first anti-Jra was described in 1970; several examples have since been found. The antigen is fully developed at birth and is resistant to treatment with ficin and papain, DTT, and glycine-acid EDTA. Anti-Jra is usually IgG. Clinical significance of anti-Jra is not well established since it is a rare antibody. One fatal case of HDFN was recently reported; in this case, the mother had previously been massively transfused, whereas in previous

The major blood group systems outside of ABO and Rh become important only after patients develop unexpected antibodies. Then a fundamental knowledge of antibody characteristics, clinical significance, and antigen frequency is needed to help confirm antibody specificity and to select appropriate units for transfusion. Only a few antibody specificities are commonly seen: M, P1, and I antibodies react at room temperature and are considered clinically insignificant; K, S, s, Fya, Fyb, Jka, and Jkb antibodies react in the antiglobulin phase and are clinically significant. These and selected others are summarized in Table 8–24. Not all antibody problems are easily solved; panel reactions are sometimes inconclusive. As described in this chapter, the existence of silent, regulator, and inhibitor genes can affect antigen expression. Hopefully the reader will find that the information in this chapter provides a starting point for serologic problem-solving. For further detailed information about the RBC antigens and antibodies described here, see Issitt and Anstee1 and Daniels.7 Resolution of antibody problems involving the unusual specificities described here may require the assistance of an immunohematology reference laboratory.

2682_Ch08_172-215 22/05/12 11:44 AM Page 209

Chapter 8 Blood Group Terminology and the Other Blood Groups

209

Table 8–24 Summary of Antibody Characteristics ANTIBODY

REACTIVITY

ENZYMES

BIND COMPLEMENT

IN VITRO HEMOLYSIS HTR

HDFN

COMPATIBLE IN U.S. POPULATION (%)

≤RT

37

AHG

M*

Most

Few

Few

Destroy

No

No

Few

Mild— severe

22

N*

Most

Few

Few

Destroy

No

No

Rare

Moderate

2B

S

Some

Some

Most

Variable effect

Some

No

Yes

Mild

45 W 69 B

s

Few

Few

Most

Variable effect

Rare

No

Yes

Mild— severe

11 W 3B

U

Rare

Some

Most

No change

No

No

Yes

Mild— severe

Modern Blood Banking & Transfusion Practices - Denise Harmening ( 6ª edition ) [PDF] | Online Book Share (2024)
Top Articles
Latest Posts
Recommended Articles
Article information

Author: Frankie Dare

Last Updated:

Views: 5622

Rating: 4.2 / 5 (53 voted)

Reviews: 92% of readers found this page helpful

Author information

Name: Frankie Dare

Birthday: 2000-01-27

Address: Suite 313 45115 Caridad Freeway, Port Barabaraville, MS 66713

Phone: +3769542039359

Job: Sales Manager

Hobby: Baton twirling, Stand-up comedy, Leather crafting, Rugby, tabletop games, Jigsaw puzzles, Air sports

Introduction: My name is Frankie Dare, I am a funny, beautiful, proud, fair, pleasant, cheerful, enthusiastic person who loves writing and wants to share my knowledge and understanding with you.