[Role of the spleen in OK-432 immunotherapy and characterization of effector cells].

: The mechanism of anti-tumor effect of OK-432 was examined in C3H/He mice transplanted with methylcholanthrene induced fibrosarcomas. Tumor growth was significantly reduced in mice treated with OK-432 daily for 7 days after tumor inoculation. Tumor growth was significantly reduced in Sham-operated mice treated with OK-432 when compared to untreated controls. On the other hand, splenectomized mice failed to respond to OK-432 immunotherapy, suggesting the spleen is an essential organ in host responsiveness to this immunostimulant. Further dissection of the mechanism of OK-432 immunotherapy was achieved by Winn assay with spleen cells taken from mice inoculated with MCA-F (1 X 10(5) cells) and OK-432 for 7 days. Spleen cells from tumor-bearing mice which had been treated with OK-432 further reduced the tumor growth compared with spleen cells from tumor-bearer and such cytotoxic activity was reduced by the spleen cells with treatment of anti-Thy 1. 2 serum plus complement or by 700 rads irradiation before Winn assay, suggesting that OK-432 generated cytotoxic T cell population in vivo.