In vitro induction of cytotoxic polymorphonuclear leukocytes by supernatant from a concanavalin A-stimulated spleen cell culture

Rat polymorphonuclear leukocytes (PMN) pretreated with supernatant of a spleen cell culture stimulated with concanavalin A (Con A sup) inhibited 3H-thymidine uptake of various syngeneic, allogeneic, and xenogeneic tumor cells. Con A sup-treated PMN were cytostatic not only to tumor cells but also to embryonal fibroblasts and normal Con A blasts. Stimulated PMN also killed some tumor cells, as shown by 3H-uridine release assay. Cytostasis by Con A sup-treated PMN began at a very early phase of incubation, but in the cytolysis assay, incubation for more than 12 hr was required to obtain significant killing. The time required for activation of cytostatic PMN by Con A sup was short (5 min was enough) if high titers of Con A sup were used for activation. PMN-stimulating activity of Con A sup was not abrogated by treatment at 60 degrees C for 30 min or by change of pH from 1 to 11. The mechanisms of cytotoxicity by Con A sup-treated PMN are discussed.