Alteration in Natural Defense Activity Against NKSusceptible B16 Melanoma Cells after Treatment with Corynebacterium parvum

We have investigated the effects of administration of C. parvum on host anti-metastatic activity against B16 melanoma H-2L, a natural killer (NK) sensitive clone with a low expression of H-2^b. The anti-metastatic activity was estimated by monitoring the following two points. One was the survival ratio at an early stage after an intravenous (iv) inoculation of radiolabeled B16 H-2L cells, the other was the formation of pulmonary metastases after iv injection with the tumor cells. Administration of C. parvum showed a biphasic change in the NK activity of the spleen cells and the peritoneal exudate cells (PEC) in mice. At an early phase (2–3 days) after administration of C. parvum, the NK activity of the spleen cells and PEC was significantly augmented. On the other hand, at a later phase (14 days) after C. parvum administration, the NK activity was deeply depressed. In correlation with NK activity of the mice treated with C. parvum, the anti-metastatic activity of the hosts was augmented in the early phase, whereas a depressed level of anti-metastatic activity was observed in the late phase after administration of C. parvum. These results suggest that the modification of NK activity is a possible basis for modulation of anti-metastatic activity by C. parvum.