[Effect of PSK on tumor-specific immunity induced by MMC-treated syngeneic tumor cells]

Immunization with MMC-treated EL-4 tumor cells could raise cytotoxic activity of non-adherent PE cells and resistance against rechallenge with small or medium doses of viable tumor cells. Administration of PSK augmented the generation of cytotoxic lymphocytes and the induction of resistance against rechallenge in mice immunized with such MMC-treated tumor cells. Augmented generation of cytotoxic lymphocytes may be ascribed to systemic effects of PSK but not to local effects in the peritoneal cavity, since augmenting effects of PSK were observed not only after intraperitoneal administration but also after oral administration. Either after intraperitoneal administration or after oral administration cytotoxic activity was detected in PE cells but not in spleen cells. Cytotoxic activity was detected in PE cells but not in spleen cells after intraperitoneal injections of MMC-treated tumor cells. Cytotoxic lymphocytes appear to differentiate to their mature form capable of being detected by 51Cr-release test principally at the site of direct graft rejection. Intraperitoneal administration of PSK was more effective in the augmentation of cytotoxicity of PE cells than oral administration. PSK may be able to have contact with precursors of cytotoxic lymphocytes more efficiently after intraperitoneal administration. Immunity against syngeneic tumor cells appears to be effective in elimination of small doses of tumor cells but to be overcome by medium or large doses of tumor cells at the rechallenge. Administration of PSK increased the threshold number to be eliminated by immune hosts. This finding seems to be important in relation to augmentation of resistance against metastasis or local implantation with a limited number of tumor cells.