ABH and Related Histo‐Blood Group Antigens; Immunochemical Differences in Carrier Isotypes and Their Distribution 1

Abstract. This review summarizes present knowledge of the chemistry of histo‐blood group ABH and related antigens. Recent advances in analytical carbohydrate chemistry (particularly mass spectrometry and NMR spectroscopy) and the introduction of monoclonal antibodies (MoAbs) have made it possible to distinguish structural variants of histo‐blood group ABH antigens. Polymorphism of ABH antigens is induced by: (i) variations in peripheral core structure, of which four (type 1, 2, 3 and 4) are known in man; (ii) variation in inner core by branching process (blood group iI), leading to variation of unbranched vs. branched ABH determinants; (iii) biosynthetic interaction with other glycosyltransferases (Lewis, P. T/Tn blood systems) capable of acting on the same substrate as the ABH‐defined transferases, and finally (iv) the nature of the glycoconjugate (glycolipid, glycoprotein of N‐ or O‐linked type). ABH variants induced by item (i) above have been clearly distinguished qualitatively by MoAbs; e.g., at least six types of A determinants can be distinguished by qualitatively different classes of antibody. The variants induced by item (ii) create mono‐ vs. bivalent antigens which may be responsible for observed differences in antibody‐binding affinity.