[Cytotoxic natural anti-tumor antibodies against fibrosarcoma and glioma cells in rats (author's transl)].

The presence of natural anti-tumor antibodies (NAA) against fibrosarcoma- and glioma cells was revealed in the normal sera of 10 different strains of rats. By means of a direct cytotoxicity test using guinea-pig complement and an absorption tests, NAA in inbred WKA/Hok rats were observed to be cytotoxically reactive to all investigated syngeneic and allogeneic fibrosarcoma lines and one glioma line, but not to hepatoma, lymphoma, leukemia, and neurinoma lines. Moreover, NAA reactivity to fibrosarcoma cells was significantly absorbed with brain, lung, kidney, skin homogenates, and cultured normal fibroblasts of syngeneic rats, but not with liver homogenates, thymus, spleen, lymph node and red blood cells. NAA were identified as being predominantly IgM and were stables at 56 degree C for 30 min. With the exception of one strain, there were no strain or sex differences in NAA levels among any of the investigated strains of rats. The level of NAA correlated with the in vivo anti-tumor response: when NAA-reactive fibrosarcoma or glioma cells were implanted into syngeneic WKA/Hok rats, groups of rats with high NAA levels suppressed tumor growth and survived longer than groups of rats with low NAA levels, while there was no difference in length of survival days in NAA non-reactive hepatoma or lymphoma cells. When 3-methylcholanthrene was inoculated into these two groups of rats, the tumor incidence in the groups of rats with high NAA level was significantly suppressed as compared to the group of rats with low NAA level. We discuss the mechanism of the induction of NAA in relation to the anti-tumor immunity.