Biology of Disease

6.6 Other Blood Group Systems

The Lewis blood group system (ISBT 007, symbol Le) is related the Lewis

antigens Lea and Leb present on erythrocytes. However, these antigens are

not integral parts of the membrane but are soluble plasma proteins which

become reversibly adsorbed onto erythrocyte membranes. The levels of

bound antigens therefore vary, although the erythrocytes of children 2 years

old and above have approximately adult levels.

The Leaand Leb antigens are not the products of different forms of a single

gene, but arise from different actions of a fucosyl transferase that attaches

fucose residues to an oligosaccharide known as type-1 precursor oligosac-

charide. If the fucose is added to a subterminal position it produces the Lea

antigen, whereas attachment to the terminal position gives the Leb antigen.

Approximately 72% of white populations are Le(a–b+), that is, they lack the

Lea but have the Leb, 22% are Le(a+b–), and 6% lack both antigens. Antibodies

to the Le antigens are usually of the IgM class and, as such, do not cause HDN

since they do not cross the placenta.

The Duffy system of blood group antigens (ISBT 008, symbol FY) is comprised

of six antigens, of which Fya and Fybare the most significant in transfusion

reactions. These antigens are expressed on an erythrocyte membrane glyco-

protein and also form the site of attachment for malarial parasites (Chapter 2).

Thus a Fy(a–b–) individual, who does not express the blood group antigens,

has a selective advantage in a malarial area. Indeed, 68% of blacks of African

descent are of this phenotype, which is rare in whites. Antibodies to Duffy

antigens belong to the IgG class and may cause HDN.

The Kidd antigens (ISBT 009, symbol JK) are expressed on a membrane glyco-

protein, which is associated with urea transport. The Jka and Jkb antigens

result from the expression of a codominant pair of genes. Approximately 27%

of whites, and 57% of blacks are Jk(a+ b–) while 50% of whites and 34% of

blacks are Jk(a+ b+). The Jk(a–b+) phenotype is found in 23% of whites and

Figure 6.9Results of Kleihauer test. The

darker staining erythrocytes are fetal cells.

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