RB, a determinant defined by lymphocytotoxicity being associated with ABO blood groups and ABH secretor status. Further evidence that RB is not produced by lymphocytes.

In a case of chimaeric male twins which showed red and white cell chimaerism, the latter being demonstrated using polymorphism of autosomes, it could be shown that the determinant RB, being defined by lymphocytotoxicity and associated with ABO blood groups and ABH secretor status, is probably absorbed from the serum on to the lymphocyte surface and not produced by the cells themselves.