ANTITUMOR EFFECT OF A BIOLOGICAL RESPONSE MODIFIER, PSK, ON C57BL 6 MICE WITH SYNGENEIC MELANOMA B16 AND ITS MODE OF ACTION/

The effects of PSK, a protein-bound polysaccharide, on the survival pe riod and effector cell activity were examined using C57BL/6 mice with melanoma B16. PSK prolonged the survival period of the mice with tumor s in a schedule- and dose-dependent manner. However, no life-prolongin g effect was observed when carrageenan-treated mice or congenitally at hymic mice were used as hosts. PSK enhanced the cytostatic activity an d interleukin-1-producing capacity of peritoneal exudate plastic-adher ent cells in C57BL/6 mice with tumors. These findings suggested that P SK prolongs the survival period of mice with B16 tumors through T-cell - and macrophage-dependent mechanisms.