T cell-specific human alloantisera-detecting antigens segregating outside the major histocompatibility complex

Two sera demonstrated non-HLA lymphocytotoxicity on the basis of reactivity with the cells of siblings genotypically identical to the serum donors for the major histocompatibility complex. These two sera, B1 and Caf, once contaminating HLA antibodies were removed by absorption with pooled platelets, demonstrated allogeneic lymphocytotoxicity that was restricted to T lymphocytes. Reactivity of the absorbed sera segregated independently of the major histocompatibility complex in 3 of 12 families tested. Unlike both cold lymphotoxins and HLA antibodies, the absorbed sera showed little temperature sensitivity against allogeneic cells, although reactivity of the B1 serum to autologous cells and to cells of the donor's HLA identical sibling did show a decrease with increasing temperature and restriction of activity to the 19S-containing fraction. Granulocytes were unreactive with the absorbed sera. Such sera may provide probes of minor transplantation antigens or markers, or both, of lymphoid subpopulations.