ANALYSIS OF THE REPERTOIRE OF HUMAN B-LYMPHOCYTES SPECIFIC FOR TYPE-A AND TYPE-B BLOOD-GROUP TERMINAL TRISACCHARIDE EPITOPES

Naturally occurring serum antibodies specific for the A and B blood group isoantigens are of great importance in medicine. By using A-type terminal trisaccharide (ATS) or B-type terminal trisaccharide (BTS) coupled to albumin as coating antigens, an enzyme-linked immunosorbent assay capable of detecting all ATS/BTS-binding antibodies was performed. The combination of this enzyme-linked immunosorbent assay with limiting-dilution methodology, using a polyclonal B-lymphocyte activator, permitted a monoclonal analysis of the human antibody repertoire that is specific for ATS and BTS in persons of different blood types. Most (78%) positive supernatants from type O cultures were monospecific for either ATS or BTS, and these were present at roughly equivalent frequencies. Nine supernatants with reactivity toward both ATS and BTS were tested by red cell adsorption; six had properties expected for true dually reactive monoclonal antibodies: adsorption with either A1 or B red cells eliminated both anti-ATS and anti-BTS activity. This finding accords with a monoclonal origin for anti-A,B. The analysis of cultures of peripheral blood lymphocytes from type A and B donors unexpectedly showed significant numbers of clones with apparent autospecificity. However, none of the anti-ATS-positive supernatants from type A cultures or anti-BTS-positive supernatants from type B cultures were adsorbable with A1 or B red cells, respectively. Consideration of only true (adsorbable) positives indicates that the type A and B anti-trisaccharide repertoires differ significantly from the type O repertoire, probably as a result of the action of normal self-tolerance mechanisms.