A small molecular weight peptide from P815 mastocytoma cells induces macrophage cytotoxicity.

Abstract

In a previous article we have shown the presence of a "factor" in the cell free exudates of intraperitoneally growing P815 mastocytoma cells as well as in cell-free tumor cell extracts. This "factor" is able to induce nonspecific macrophage cytotoxicity against tumor target cells. The "factor" was sensitive to heating at 100 degree C for 1 min, destroyed by pronase treatment, and dialyzable. On the other hand, the "factor" was not removed by centrifugation (25,000 x g), and was resistant to chloroform extraction, ultraviolet irradiation, heating at 56 degree C (for 20 min), or RNAase treatment. Sephadex gel fractionation of the mastocytoma exudate showed that the "factor" has an approximate molecular weight of 650-700 daltons. Normal peritoneal macrophages incubated with an extract of murine mast cells, purified histamine or serotonin did not show detectable cytotoxicity against tumor cells. The results of our experiments suggest that the effect of the P815 cell-free exudate and tumor cell extract is due to a dialyzable small molecular weight peptide.