Complement origin determines lytic activity of antibodies to nucleated target cells. Comparison of common complement...

The effects of complement from different species of animals were measured in a variety of antibody assays by using 51Cr-labelled target cells. Sheep antibodies were measured in samples of lymph and serum obtained from animals immunised with allogeneic lymphocytes, transplanted with allogeneic kidney grafts, or immunised with mouse tumour cells. Mouse (C57BL) antibodies were measured after immunisation with allogeneic tumour (P815) or after transplantation of allogeneic thyroid grafts (BALB/c). Different species of complement gave quantitative and sometimes qualitative differences when used to assay the same samples of antibody. In all systems tested, rabbit complement caused lysis of target cells at low antibody concentration when guinea pig and rat complements gave negative results, in some antibody-target cell combinations sheep complement was as effective as rabbit complement in mediating lysis. The different complement sources showed no selective lytic affinity for either IgM or IgG1 antibody subclasses purified from immune sheep lymph. Lysis of P815 target cells occurred more quickly when mediated by rabbit or sheep complement than when mediated by guinea pig or rat complement. Complement-dependent lysis sometimes occurred in systems where antibody, target cells and complement were obtained from the same species.