Murine peritoneal exudate cells were activated by OK 432 and produced the cytotoxic or cytostatic factors exhibiting a considerably potent anti-tumor activity: A significant reduction of DNA synthesis in syngeneic hepatoma cells was observed when tumor cells were incubated in the presence of culture supernatant taken from peritoneal exudate cells activated with OK 432 or LPS. The active substance was fractionated into a definitive fraction by gel filtration using a Sephadex G-75 column and this was further fractionated into two active fractions by DEAE-cellulose column chromatography.
These results suggested that OK 432 might suppress the tumor cell growth through activation of macrophages and production of cytotoxic or cytostatic factors from the activated macrophages.