Induction of tumoricidal peritoneal exudate cells by administration of Lactobacillus casei

The lifespan of mice into which Meth A fibrosarcoma was transplanted intraperitoneally (i.p.) was prolonged by i.p. treatment with Lactobacillus casei YIT 9018 (LC 9018). Treatment with LC9018 before the tumor inoculation (pre-treatment), was more effective than after the tumor inoculation (post-treatment). When tumor cells were inoculated subcutaneously along with peritoneal exudate cells (PEC) harvested from LC 9018-treated mice in the Winn type test, the tumor growth was significantly inhibited, but it was not inhibited by spleen cells. Adherent and nonadherent cells of LC 9018-induced PEC suppressed tumor growth in the Winn type test. PEC induced with LC 9018 showed significant cytolytic activity for 51Cr-labeled Meth A from 3 days to at least 2 weeks after a single injection of LC 9018. The adherent cells lysed tumor cells in the cytolytic test, though nonadherent cells did not show cytolytic activity. These results show that LC 9018 can induce two cell populations possessing the ability to kill tumor cells in vivo. One may be activated macrophages which directly kill tumor cells and the other may be T-lymphocytes which can induce cytotoxic cells.