Extracellular cytolysis by activated macrophages and granulocytes. II. Hydrogen peroxide as a mediator of cytotoxicity.

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Abstract
When deprived of oxygen, BCG-activated [mouse] macrophages no longer lysed P388 lymphoma cells. H2O2 release and cytotoxicity by BCG-activated macrophages and by granulocytes triggered with phorbol myristate acetate (PMA) were markedly inhibited when the glucose concentration in the medium was reduced to 0.03 mM or less, or if glucose were replaced with galactose. Catalase abolished PMA-triggered cytotoxicity by both types of effector cells, whereas superoxide dismutase had no effect. Ferricytochrome C reduced the cytotoxicity of BCG-activated macrophages, an effect which was largely reversed by superoxide dismutase. Cytotoxicity was not affected by 10 drugs thought to quench singlet oxygen and/or scavenge hydroxyl radical. Neither azide nor cyanide reduced cytolysis, but there was marked inhibition by lactoperoxidase and iodide. Cytoxicity may not depend on myeloperoxidase. Lactoperoxidase may have diverted H2O2 from the oxidation of target cells to oxidation of substances in serum. Mouse erythrocytes, although sensitive targets, interfered with the cytolysis of lymphoma cells, probably by competition for H2O2. Starch particles with covalently bound glucose oxidase resembled macrophages in their spatial relation to the target cells and in the flux of H2O2 they generated from their surface, but were not expected to produce any other potentially toxic products. Such particles lysed lymphoma cells, and the lysis was prevented by catalase. Neither arginase nor thymidine appeared to be involved in cytolysis by BCG-activated macrophages under the conditions used. Release of H2O2 was necessary and sufficient for cytolysis by BCG-activated macrophages or granulocytes when pharmacologically triggered.