Alteration in natural defense activity against NK-susceptible 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-2b. 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.