Cytotoxic and enhancing properties of early gammaM alloantibodies elicited by first set renal allografts. In vitro and in vivo studies with rat and guinea pig complement on somatic target cells with varying antigen density.

First set rat renal allografts transplanted over the strong Ag-B histocompatibility locus elicit antibodies of the gammaM class demonstrable at the time of graft rejection. These early gammaM alloantibodies with guinea pig complement are cytotoxic in vitro to high antigen density target cells like lymph node cells and splenocytes but not to low antigen density target cells like thymocytes and bone marrow cells. With rat complement, gammaM alloantibodies are required in far greater amounts to kill some high density target cells. This in vitro discrepancy between rat and guinea pig complement is not caused by the presence of natural antibody in guinea pig serum nor by a deficiency of complement components in rat serum, but is dependent on the antigen antibody interaction studied. In vivo studies show early gammaM alloantibodies to be cytotoxic to donor lymphoid cells but to enhance renal allografts. These cytotoxic and enhancing qualities reside in the same preparation of immunoglobulin and are influenced by antigen density. These studies suggest that the failure to damage donor kidneys by early, probably low avidity, antibody is caused by a low concentration of antigen on the endothelial cells within the renal graft, and or an inability of this antibody antigen interaction to activate syngeneic complement.