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| >> Blood Group Determinants |
In 1901, Karl Landsteiner discovered blood group antigens. Since that time nearly 200 antigens have
been identified. Carbohydrate-dependant blood group antigens are carried by both glycoproteins and
glycolipids -- some well known carbohydrate antigens belong to the ABO(H), Lewis (Le), and Ii blood
group systems.
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| ABO(H) System |
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The ABO(H) system of blood group determination consists of three antigens, H, A, and B, and
is the most important in blood transfusions. The H antigen is a disaccharide,
Fuc-a2-Gal. a3 Linkage of GalNac to the galactose
of the H structure forms the A antigen, while linkage of Galactose in that position forms the B
antigen. Gene coding for a2-fucosyltransferase determines formation of
the H antigen, while coding for a3-GalNAcT and a3-GalT
transferases determines formation of A and B antigens, respectively. Some individuals lack the ability
to synthesize H antigen due to a defective FucT gene; these people are classified as "Bombay-type".
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| Lewis (Le) System |
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Fucosylated drivatives of Gal-GlcNAc comprise the Lewis (Le) system. The two types of antigen
in this system are monofucosylated trisaccharides, Lea and Lex, and
difucosylated tetrasaccharides, Leb and Ley. The a and b antigens are
isomeric in linkages to the x and y antigens, respectively (See table in diagram). The sialated
form of Lex is also very important as a recognition marker for selectins. Important
fucosyltransferases are involved in the Lewis Antigens'
biosynthesis
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