Non-activated rat neutrophils kill syngeneic colon tumor cells by the release of a low molecular weight factor

The mechanisms of cancer cell destruction by unelicited peripheral blood neutrophils has never been reported in a syngeneic model. We demonstrated that in vitro, unelicited polymorphonuclear neutrophils isolated from rat blood were toxic against syngeneic colon cancer cells. The tumor cell lysis was not due to oxygen metabolites released by PMNs, but was due to a cytolytic factor. This factor was spontaneously secreted by PMNs, was heat-stable and had a low molecular weight (less than 10 kD). Its partial inhibition by chymotrypsin and/or chymotrypsin-like proteases suggested a peptidic structure of this factor.