Further evidence for the presence of A antigen on group B erythrocytes through the use of specific exoglycosidases.

Certain antibodies have shown the ability to detect small amounts of A antigenic structures on certain group B cells. These rare cells that reverse group as B, are designated here as B(A) cells. Among the anti-A antibodies capable of detecting these cells are MHO4 (an IgM murine monoclonal antibody) and polyclonal anti-A derived from blood group O donors. The latter (anti-A, B) have been adsorbed exhaustively with normal B cells, to deplete the serum of antibodies to group B antigen. The cell specificity detected by these antibodies can be removed only by an alpha-N-acetylgalactosaminidase (A-zyme) but not by an alpha-galactosidase (B-zyme). Inhibition studies show that these reactions can be inhibited by A secretor saliva and cannot be inhibited by B secretor saliva. Moreover, papain treatment of normal group B cells not previously agglutinable with these antibodies, now causes these cells to become reactive, and this specificity, too, is removed only by A-zyme. These results suggest that low levels of blood group A antigen are being recognized by these antibodies and that these structures can exist not only on B(A) cells but on all group B erythrocytes.