Mouse serum inhibition of cytotoxicity of goat antibodies against mouse thymocytes]

It is shown that the serum of Balb/c, C57Bl/6 and F1(C57Bl/6 x CBA) mice inhibits cytotoxicity of goat antithymocyte antibodies. The addition of the serum into the incubation medium increases the proportion of alive cells from -5% up to 95%. Cytotoxicity was also inhibited by the globulin fraction of the mice serum. It is suggested that normal mice serum contains factors which block cytotoxicity of antibodies against antigen host determinants.