Rapid inactivation of tumor killing factor in vitro.

The mechanism of the rapid inactivation of the cytotoxic activity produced by peritoneal macrophages stimulated with Sarcophaga lectin was investigated. Experiments using radioiodinated tumor killing factor (TKF) showed that the main reason for its inactivation was the rapid dissociation of its trimeric structure into 15-kDa subunits. This dissociation was found to proceed spontaneously in the culture medium irrespective of the presence of macrophages.