[The mechanism of the antitumor action of Bacillus intermedius ribonuclease].

In a concentration providing the maximum in vivo antitumor action, "Bacillus intermedius" RNAase had no in vitro cytotoxic effect on the cells of lympholeukosis NK/Ly. The enzyme did not inhibit the involvement of 3H-thymidine in the DNA biosynthesis in the tumor cells cultivated in vitro. A preliminary in vitro exposure of the cells to the enzyme did not influence their inoculation capacity. It was concluded that the mechanism of the enzyme antitumor action was not associated with the inhibition of the tumor cell viability. It was shown to be due to the activation of the intermediate effector system. The suggested mechanism of the mediated RNAse action on the tumor growth includes stimulation of the host immunity or removal/restriction of the tumor systemic action on the host.