In vitro stimulation of lymphocytes by neutral proteinases from human polymorphonuclear leukocyte granules

Two neutral proteinases, polymorphonuclear leukocyte (PMN) elastase and cathepsin G, were purified from azurophil granules of human PMN. Both enzymes were found to stimulate both human and mouse lymphocytes in vitro. Experiments with mouse cells showed that the PMN proteinases are B-cell stimulants. Stimulation appears to depend on direct proteolytic action on the lymphocyte surface and not to require the mediation of serum factors of the help of T-cells.