ABH antigens one of the systems of blood group antigens having determinants associated with oligosaccharide structures. It is the basis of the ABO system, which was the first human blood group antigen system to be detected, by Austrian-born US pathologist Karl Landsteiner (1868–1943) in 1901, and it remains the most important in blood transfusion. Individuals having neither A nor B antigen express the H antigen, the product of an independent gene belonging to the Hh system. Antigens of the ABH system are oligosaccharide chains, in the erythrocyte carried on band 3 (the anion transporter) and band 4.5 (the glucose transporter), or on ceramide. A highly branched N-glycan, consisting of a trimannosyl-di-N-acetyl-chitobiosyl core with Gal(b1-4)GlcNAc(b1-3) repeats, forms the basis of ABH antigens. The H determinant is the precursor; antigen A is formed by addition of N-acetyl-D-galactosamine by fucosylgalactose a-N-acetylgalactosaminyltransferase (EC 2.4.1.40); antigen B is formed by addition of D-galactose by fucosylglycoprotein 3-agalactosyltransferase (EC 2.4.1.37). The terminal sugar residues of importance are: H determinant, Fuc(a1-2)Galb-R; A determinant, GalNAc(a1-3)(Fuca1-2)Galb-R; B determinant, Gal(a1-3) (Fuca1-2)Galb-R. The enzyme responsible for adding the terminal fucosyl residue of the H determinant is galactoside 2-a-L-fucosyltransferase (EC 2.4.1.69).
