The A₁ (B) phenomenon: a monoclonal anti‐B (BS‐85) demonstrates low levels of B determinants on A₁ red cells

Abstract

A monoclonal anti-B (BS 85) that reacts strongly with red cells from weak B variants (B3, Bint and Bv) has demonstrated the presence of a trace of B on A1 red cells. The agglutination of group A1 red cells by an anti-B antibody is called the A1 (B) phenomenon and is the converse of the B(A) phenomenon seen with certain monoclonal anti-A antibodies. Fragile A1 (B) agglutination is best seen by spin-tube techniques and A1 red cells negative in saline tests are agglutinated by albumin and protease enzyme-enhanced tests, but no reactions are seen with A2 red cells. The A1 (B) reaction is specifically inhibited by B substance, and D-galactose and the galactose-containing sugars melibiose and lactose. Red cells from B variants showed differential inhibition patterns with various sugars. A1 transferase levels were normal even in the strongest A1 (B) reactive blood samples, although the plasma H transferase levels and H status of these red cells were elevated. This is in contrast to the B(A) phenomenon which is associated with elevated levels of B transferase. It is suggested that A1(B) overlapping specificity can occur because of a combination of higher H activity (and thus more H sites) together with normal levels of A transferase activity as they are 20% higher than normal levels of B transferase. The production of anti-B reagents free of the A1 (B) phenomenon with BS-85 is achieved by suitable dilution using quality control tests with protease-treated A1 red cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Many genetically defined ABO subgroups exhibit characteristic flow cytometric patterns

“…The original report used papain‐treated A 1 RBCs but neither the anti‐B clone selected by us as the most sensitive one (9621A8) nor a fresh batch of BS‐85 (a kind gift from Biotest, Dreieich, Germany) was able to stain group A 1 cells by flow cytometry. By immediate‐spin agglutination we could only detect very weak microscopic reactions with BS‐85 and papain‐treated A 1 cells (data not shown), in contrast to the 2+/3+ reaction reported by Voak and colleagues 45 . It is therefore possible that the B antigen sensitivity in this study is lower than that for A antigen.…”

“…By immediate-spin agglutination we could only detect very weak microscopic reactions with BS-85 and papain-treated A 1 cells (data not shown), in contrast to the 2+/3+ reaction reported by Voak and colleagues. 45 It is therefore possible that the B antigen sensitivity in this study is lower than that for A antigen.…”

“…44 However, the specificity of this reactivity was confirmed by treatment of group B RBCs with exoglycosidase specific for A antigen after which these cells typed and stained negatively with ES-15. 20,21 We were unable to reproduce the weak B reactivity once reported 45 in group A1 RBCs with the anti-B clone BS-85. The original report used papain-treated A1 RBCs but neither the anti-B clone selected by us as the most sensitive one (9621A8) nor a fresh batch of BS-85 (a kind gift from Biotest, Dreieich, Germany) was able to stain group A1 cells by flow cytom-etry.…”

ABO, H, and Lewis Systems

“…One monoclonal anti -B brought about agglutination of 1.42% of group A red cell samples, all A 1 , and this was considered to represent A(B) phenotype; B activity resulting from GTA 1 activity [388] . A(B) was not associated with elevated GTA activity, but A 1 (B) cells did have elevated levels of H antigen and plasma H -transferase activity.…”

False‐positive reactions of some monoclonal anti‐c reagents

“…False‐positive reactions of monoclonal reagents cannot be completely excluded though: the B(A) and the A1(B) phenomena are caused by an avidity of some monoclonal antibodies that is too high for practical purposes (Voak, 1987; Voak et al ., 1992). Some other monoclonal reagents show cross‐reactivities with different antigens because of the similarity of the structure of some carbohydrate antigens, e.g.…”