The Two Antibody Specificities Within Human Anti-Blood Group B Antibodies

Abstract

ANTIBODIES to blood group antigens have been regarded as natural anticarbohydrate antibodies with an absolute specificity to the wellcharacterized blood group A or B antigenic epitopes.I ,2 However, long before the determination of blood group antigen structures, Landsteiner and Miller observed that anti-B antibodies are in fact heterogeneous antibodies recognizing more than one antigen. They found that whereas New World monkey red cells are agglutinated byhuman anti-B antibodies, these red cells do not bind anti-B antibodies from sera of rabbits immunized with Bred cells. 3 This suggested that human anti-B sera contain, in addition to antibodies reacting with B antigen, antibodies directed toward a different antigenic structure that closely resembles B antigen, designated B-like antigen. B-like antigen was assumed to be present on New World monkey red cells, but absent from human, ape, and Old World monkey red cells. 3 These early observations were confirmed thereafter by other investigators as well. 4 Furthermore, Owen found that rabbit red cells also express B-like antigen, which can adsorb only a portion of human anti-B antibody reactivity. The fact that B-like antigen on rabbit red cells is different from B-antigen on human red cells was also evident from the finding that after immunization with B red cells, rabbits produce highly reactive anti-B antibodies. 3,7 The present work reviews some of our recent studies that explain the Band B-like specificities of antibodies within human anti-B sera. We found B-like antigen to be the Galal~3Gal epitope, which differs from B antigen in lacking the fucosyl residue which, in B antigenic epitopes, are linked