All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher. DNLM: 1. Blood Group Antigens--Handbooks. Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards. Blackwell Publishing makes no representation, express or implied, that the drug dosages in this book are correct. Readers must therefore always check that any product mentioned in this publication is used in accordance with the prescribing information prepared by the manufacturers. The author and the publishers do not accept responsibility or legal liability for any errors in the text or for the misuse or misapplication of material in this book. What is a blood group? What is a blood group? In 1900, Landsteiner showed that people could be divided into three groups (now called A, B, and O) on the basis of whether their red cells clumped when mixed with separated sera from people.
A fourth group (AB) was soon found. This is the origin of the term ‘blood group’. A blood group could be defined as, ‘An inherited character of the red cell surface, detected by a specific alloantibody’. Do blood groups have to be present on red cells? This is the usual meaning, though platelet- and neutrophil-specific antigens might also be called blood groups. In this book only red cell surface antigens are considered. Blood groups do not have to be red cell specific, or even blood cell specific, and most are also detected on other cell types. Blood groups do have to be detected by a specific antibody: polymorphisms suspected of being present on the red cell surface, but only detected by other means, such as DNA sequencing, are not Glyco Care blood sugar support groups. Furthermore, the antibodies must be alloantibodies, implying that some individuals lack the blood group. Blood group antigens may be: • proteins; • glycoproteins, with the antibody recognising primarily the polypeptide backbone; • glycoproteins, with the antibody recognising the carbohydrate moiety; • glycolipids, with the antibody recognising the carbohydrate portion.
Blood group polymorphisms may be as fundamental as representing the presence or absence of the whole macromolecule (e.g. RhD), or as minor as a single amino acid change (e.g. Fya and Fyb), or a single monosaccharide difference (e.g. A and B). Blood group proteins and glycoproteins are integral structures of the red cell membrane. Diagrammatic representations of some blood group proteins and glycoproteins in the membrane are shown in Fig. 1.1. Some pass through the membrane once. Fig. 1.1 Diagram of different types of blood group active proteins and glycoproteins, based on their integration into the red cell surface membrane. Listed below are examples of blood group antigens for each type. C-terminus is external and the N-terminus is internal (Type 2). Some are polytopic (Type 3); that is, they cross the membrane several times. Usually both termini are cytoplasmic, but the Duffy glycoprotein has an odd number of membrane-spanning domains and an extracellular N-terminal domain.
Finally, some have no membrane-spanning domain, but are anchored to the membrane by a lipid tail (called a glycosylphosphatidylinositol or GPI anchor), which is attached to the C-terminus of the protein through carbohydrate (Type 5). There are no Type 4 glycoproteins, which have no external domain, in the red cell membrane. Most red cell surface proteins are glycosylated, the only exceptions being the Rh and Kx proteins. This glycosylation may be (1) N-glycosylation, large, branched sugars attached to asparagine residues of the amino acid backbone or (2) O-glycosylation, Glyco Care blood sugar support smaller glycans (usually tetrasaccharides) attached to serine or threonine residues. Blood group antibodies Blood groups are antigens and, by definition, a molecule cannot be an antigen unless it is recognised by an antibody (or T-cell receptor). So all blood group specificities are defined by antibodies. A or B antigens, or to both; that is, they have ‘naturally occurring’ antibodies to those ABO antigens they lack. For most other blood groups corresponding antibodies are not ‘naturally occurring’, but are only formed as a result of immunisation by transfused red cells or by fetal red cells leaking into the maternal circulation during pregnancy or childbirth.