Cationic proteins purified from human polymorphonuclear leukocyte granules exert a cytotoxic effect on mammalian tumor cells. This effect is time and concentration dependent, is inhibited by the anionic agent heparin, and is enhanced by preheating the cationic proteins. Other strongly basic proteins (histone, protamine) also exhibited cytotoxic activity. Myeloperoxidase isolated from human leukocytes is cytotoxic when combined with H2O2 and chloride. Under these conditions, the potency of the myeloperoxidase-mediated system is greater than that of the cationic proteins.

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