Antigenic sites of Bg^a specificity have been demonstrated on leucocytes as well as on red cells. The Bg^a group shows almost complete concordance with the histocompatibility group HL-A7. Red cells show much less activity than leucocytes and did not absorb cytotoxic antibodies but leucocytes removed all haemagglutinating activity. RNAP reactions can be demonstrated by both haemagglutination and cytotoxic tests. In some instances multispecific cytotoxic antibodies may show a monospecific haemagglutinating component. Family studies showed that the HL-A groups may influence the Bg^a reaction of the red cells.

Antigenic sites of Bg^b and Bg^c specificity are present on lymphocytes as well as on red cells. The Bg^b group has been correlated with the W17 (Te57) white cell group, and the Bg^c with the W28 (Da15,Ba*) antigen. Both haemagglutinating and cytotoxic antibodies can be absorbed by either red or white cells, though cross-reactivity was shown by many white cells. A haemagglutinin reacting with HL-A10 positive donors was found in some multispecific antisera. All these groups show weaker reactions with red cells than with lymphocytes.