Enhancement of Polymorphonuclear Leukocyte‐mediated Tumor Cytotoxicity by Serum Factor(s)

It has been reported that β‐1,3‐d‐glucan isolated from Alcaligenes faecalis (TAK) promoted tumor cytolysis by mouse polymorphonuclear leukocytes (PMN). We investigated the effect of serum on mouse PMN tumor cytolysis induced by TAK and other PMN stimulators. Addition of fetal calf serum (FCS) to the cytolysis assay enhanced tumor cytolysis by PMN in a dose‐dependent manner. Sera obtained from horses, mice, and rats were also effective enhancers of PMN tumor cytolysis. When FCS was added after the assay was under way, the enhancing effect decreased proportionally to the time elapsed. The enhancing activity was detected over a broad range of fractions with a peak at 170 kD by fractionation on a Superose 6 column. The responsible factor(s) in serum was stable after treatment at 60°C, 30 min or after lowering the pH to 2. Mouse PMN stimulated with TAK increased production of hydrogen peroxide in the presence of FCS.