Effect of Krestin (PSK) on the induction of IL-2 activated killer cells.

The effects of Krestin (PSK) on the generation of lymphokine-activated killer (LAK) cells were examined in tumor-bearing mice. BALB/c mice were inoculated subcutaneously with methylcholanthrene-induced fibrosarcoma (Meth A) cells, and PSK was administered intraperitoneally every other day. The reduced LAK activity in tumor-bearing mice was restored by the administration of PSK. Since involvement of the humoral immunosuppressive factor in the impairment of LAK activity has been suggested, the effect of PSK on the impaired LAK activity in the presence of an immunosuppressive factor isolated from the ascites of X5563 (plasmacytoma)-inoculated mice was examined. The activity reduced by the immunosuppressive factor in an in vitro induction of LAK was restored by incubation with PSK. The antimetastatic effect of IL-2 was also augmented by its combined use with PSK. The data provide a rational basis for using PSK in combination with recombinant IL-2 in cancer immunotherapy.