Blood group antigens are structures on the outer
surface of human red blood cells (RBCs) that can be recognized by
the immune system of individuals who lack that particular structure.
Identification of RBC antigens and antibodies has been the basis
of pretransfusion compatibility testing and the safe transfusion
practices used today and also can provide insights into understanding
the etiology of hemolytic disease of the fetus and the newborn.
Biochemical and molecular studies have led to definition of the
biologic functions of molecules expressing blood group antigens.
These molecules play a critical role in susceptibility to infection
by malarial parasites, some viruses, and bacteria. Alteration of
RBC antigen expression is associated with many molecular backgrounds
and some play a role in the clinical manifestations of certain diseases.
Erythrocytes, far from being inert containers of hemoglobin, are
active in a variety of physiologic processes.
Acronyms and Abbreviations
Acronyms and abbreviations that appear
in this chapter include: AET, 2-aminoethylisothiouronium bromide;
CD, cluster of differentiation; DTT, dithiothreitol; GPA, glycophorin
A; GPB, glycophorin B; GPC, glycophorin C; GPD, glycophorin D; GPI,
glycosyl phosphatidylinositol; HDFN, hemolytic disease of the fetus
and newborn; HEMPAS, hereditary erythroblastic multinuclearity with
a positive acidified serum test; Ig, immunoglobulin; ISBT, International
Society of Blood Transfusion; LAD, leukocyte adhesion deficiency;
2-ME, 2-mercaptoethanol; PNH, paroxysmal nocturnal hemoglobinuria;
RBC, red blood cell.
A blood group system consists of a group of antigens encoded by alleles at a single gene locus or at gene loci
so closely linked that crossing over does not occur or is very rare.
An antigen collection consists of antigens that
are phenotypically, biochemically, or genetically related, but the genes
encoding them have not been identified.1 Placement
of a blood group antigen into a system or collection begins with
the discovery of an antibody, usually in the serum of a multiparous
woman or a multiply transfused recipient, with a unique pattern
of reactivity. The antibody can be used to study basic biochemical
properties of the corresponding antigen, to enable recognition of
the pattern of inheritance of the antigen in families and in populations,
to identify red blood cells (RBCs) that lack the antigen, and to
search for an antithetical antigen. Identified characteristics,
such as prevalence of positive reactions or sensitivity or resistance
to specific enzymes, are compared to known systems and collections.
A newly recognized antigen is also evaluated using biochemical and
molecular genetic methods.
The majority of genes encoding blood group antigens have been
cloned and sequenced,2 and the molecular bases
of most blood group antigens have been determined.3–6 Details
on the alleles associated with blood group antigens and phenotypes
can be obtained from the following National Center for Biotechnology
Information (NCBI) “dbRBC” website: http://www.ncbi.nlm.nih.gov/gv/mhc/xslcgi.cgi?cmd=bgmut/home.
RBC blood group antigens are inherited carbohydrate or protein
structures located on the outside surface of the RBC membrane (Fig. 137–1). Although most of the
protein blood group antigens ...