Serological studies of the H activity of Oh red cells with various anti-H reagents

Mouse monoclonal IgM antibody against human lung cancer line SK-LC-3 with specificity for H(O) blood group antigen

Spleen cells from mice immunized with the human lung cancer line SK-LC-3 were fused with mouse NS-1 myeloma cells. One of the hybrid clones produced a monoclonal IgM antibody (designated F-3), detected with antimouse Ig-MHA and hemagglutination assays. This antibody was completely absorbed by O red cells and completely inhibited by low concentrations of H(O) glycoproteins and hog mucin (A + H). Bombay (Oh) red cells completely failed to absorb F-3 activity even after treatment with neuraminidase. A1, A2, A1B, A2B, and B red cells and A- and B-glycoproteins were less effective in absorbing or inhibiting F-3 activity. Other glycoproteins (including those having Lea or blood group precursor structures) showed little or no inhibitory activity. Serum from nude mice carrying F-3 hybridoma agglutinated O and A2 red cells at a titer of 1:40,000 and 1:640, respectively. A1, A1B, A2B, and B red cells were agglutinated with titers of 1:80 or less. Monoclonal antibody F-3 is, therefore, highly specific for H(O) blood group determinants.

Probable biosynthetic pathway for the synthesis of the B antigen for Bh variants

Red cells and serum from two Bh variants (B+H-cells) have been investigated for B and H blood group glycosyltransferases. The H enzyme could not be detected using either type 1 or type 2 chain acceptors. The B enzyme was present in normal amount when 2'-fucosyllactose was used as substrate, neither 6'-fucosyllactose nor 6'-fucosyllactosamine could act as acceptors for the B enzyme. Upon treatment of the Bh red cells by the B-degrading enzyme from Trichomonas foetus the B antigen was destroyed while H determinants were uncovered (B-H + cells). The cells thus treated could be further converted into A&H-red cells by the action of the A transferase from human blood group A serum. Previous treatment of the B-H + cells by the H-degrading enzyme from T. foetus, however, led to B-/-erythrocytes and prevented their conversion into A red blood cells by the A enzyme. The results clearly demonstrate that, as found in normal B individuals, the B antigen from Bh cells is built up from the H precursor and provide additional evidence that H is not a completely silent gene in Bh individuals.