Two anti-tumour cytotoxic cells in the peritoneal cavity of rats: natural occurrence, augmentation and partial characterization.

Mononuclear cells cytotoxic to methylcholanthrene-induced fibrosarcoma cells were detected in the peritoneal cavities of normal rats by means of 16 h 51Cr release and 48 h 125IUdR release assays. Carriage of a tumour which induces concomitant immunity, or intraperitoneal injections of Corynebacterium parvum or proteose-peptone, led to increases in mononuclear cell numbers. Injections of C. parvum and proteose-peptone led to increases in cytotoxicity in 51Cr release assays. Carriage of an immunogenic tumour led to an increase in cytotoxicity to homologous tumour cells in the 125IUdR release assay. Cells were separated by sedimentation velocity, metrizamide density gradients and adherence to glass or plastic. Small cells were more active than large cells in 51Cr release assays. Larger cells tended to be more active in 125IUdR release assays. Generally, low density cells were more active in both assays, except that high density cells induced by C. parvum were most active in 125IUdR release. Adherent cells from C. parvum-injected rats were more active than non-adherent cells in both assays. On the basis of differential stimulation and separation by sedimentation velocity it is suggested that two cell types, possibly NK cells and macrophages, are operative. 125IUdR-labelled fibrosarcoma cells were lysed after intraperitoneal injection into normal and concomitantly immune rats, more rapidly extensively in the latter case. These cytotoxic cells may be important in both natural and acquired resistance of rats to tumour growth.