SUPPRESSION OF HEPATIC NATURAL-KILLER ACTIVITY BY LIVER METASTASIS OFCANCER AND RESTORATION OF KILLER ACTIVITY BY ORAL-ADMINISTRATION OF ABASIDIOMYCETES-DERIVED POLYSACCHARIDE, PSK

PSK (Krestin) is a protein-bound polysaccharide with antitumor and imm unomodulatory activity. In this study, the effects of the oral adminis tration of PSK were investigated on the natural killer (NK) activity o f liver-associated lymphocytes and their subfractions separated by den sity gradient centrifugation, in WKAH rats with liver metatasis of KDA hepatoma. PSK was administered orally, at a dose of 500 mg/kg once a day for 3 weeks. The NK activity of nonparenchymal liver cells (NPLC) and their subfractions, including large granular lymphocytes (LGL), wa s markedly augmented by this treatment. The effects of oral PSK were a lso examined in CDF1 mice with liver metastases of Colon 26 adenocarci noma; the survival of tumor-bearing mice was prolonged and both metast atic foci and liver weight were decreased. These results suggest that PSK may be effective for the suppression of liver metastasis through a ctivation of liver-associated NK cells.