Antitumor effect of OK-432 (3)--mechanisms of tumor growth inhibition by OK-432 induced activated macrophages

Spleen cells and peritoneal exudate cells obtained from BALB/c mice which had received an i.p. injection of 0.1 mg of OK-432 4 days previous to sacrifice, were examined by Winn's neutralization assay for their antitumor activity against Meth-A sarcoma cells in BALB/c mice. Both of the cell preparations clearly inhibited the growth of admixed Meth-A cells, but when these same cell populations were treated on a Sephadex G-10 column, the effector activity seen in Winn's assay disappeared. The effector cells responsible for tumor inhibition were therefore considered to be cytotoxic macrophages. However, the inhibitory effect of these cytotoxic macrophages in Winn's assay was not evident in either X ray (300 rad)-irradiated BALB/c mice or in nu/nu BALB/c mice. These results indicate that the antitumor activity of cytotoxic macrophages is associated with a sequential immune mechanism in which T cells may play an important role.