[Tumor-regressing factor induced by antitumor polysaccharide in the serum of tumor-bearing mice].

A potent tumor-regressing activity was found in the serum of mice with S180 tumor undergoing rapid regression caused by antitumor polysaccharides. Beta (1-3) glucan including CM-TAK and lentinan and mannoglucan MGA induced such activity. It causes a rapid decrease in the number of tumor cells accompanied with a marked increase in neutrophiles in solid tumors. The entity of the activity was named as tumor-regressing factor (TRF) and was partially purified revealing a proteinaceous nature with an approximate molecular weight of 250,000. The factor was induced in a serum of tumor-bearing mice in various host-tumor combinations after the tumor growth had been established but only weakly in normal mice. The sensitivity of tumors to the factor was also dependent on the stage of tumor growth. The serum of normal mice or tumor-bearing mice without polysaccharide treatment exhibited similar activity as TRF after definite chromatographic step. The chromatographic behavior of the revealed activity was closely similar to that of the induced factor. It was postulated that a TRF-like activity exists in normal serum in a inactivated form being bound by antagonist(s) and the appropriate chromatography might remove the antagonist resulting in the active form of the factor. The concept was confirmed by reconstituting the chromatographic fractions, the revealed activity was again obscured after mixing with a certain fraction.