Effects of PSK on specific tumor immunity to syngeneic tumor cells.

Substantial degrees of resistance against rechallenge with viable tumor cells and cytotoxic activity of peritoneal exudate cells (PE cells) as detected by in vitro 51Cr-release test or in vivo Winn's test were raised by immunization with Mitomycin C-treated EL-4 tumor cells in syngeneic C57BL/6J mice. Cytotoxicity of PE cells was found to reside in glass-nonadherent and anti-Thy 1.2-sensitive population, while such activity was not detected within the spleen and mesenteric lymph nodes. Intraperitoneal or oral administration of PSK augmented such resistance or cytotoxicity.