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Human monocyte mediated tumor cyto toxicity 1. demonstration of an oxygen dependent myelo peroxidase independent mechanism



Human monocyte mediated tumor cyto toxicity 1. demonstration of an oxygen dependent myelo peroxidase independent mechanism



Journal of Immunology 132(4): 1980-1986



De novo human monocyte-mediated tumor cytotoxicity and that induced by the agent 12-O-tetradecanoylphorbol-13-acetate (TPA) were studied. Cytolytic function was analyzed by reference to the release of [111In] oxine from 2 prelabeled tumor [human leukemia] cell lines, K562 and U937, in a 16-h assay. Observed cytolysis was clearly related to TPA concentration and effector cell number. Maximal cytolysis was obtained with TPA at 5 ng/ml. Unstimulated monocytes expressed minimal cytolytic activity. When TPA-stimulated monocyte-mediated cytolysis was examined, catalase inhibited K562 and U937 cytolysis by 92 and 84%, respectively while superoxide dismutase only inhibited cytotoxicity by 17 and 24%, implicating a central role of H2O2 rather than superoxide ions. Sodium azide [1 mM], an inhibitor of myeloperoxidase, increased K562 and U937 cytolysis by 34 and 57%. This increased cytotoxicity was observed for K562 at low levels of cytotoxicity. These data tend to dismiss an essential role of the H2O2-halide-myeloperoxidase pathway of cytolysis. The OH scavengers, histidine and ethanol, did not affect K562 killing; mannitol, another OH scavenger, had only a slight inhibitory effect (23%). H2O2 generated by a glucose-glucose oxide system directly mediated K562 killing and, to a lesser extent, U937 lysis. The results point strongly towards the role of a myeloperoxidase-independent mechanism of cytotoxicity, with H2O2 as a key mediator of the cytolytic mechanism, and a limited role of O2- in synergy with H2O2 in the cytolytic activity of monocytes, and suggest that significant cytolytic function requires an inductive event.

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Accession: 005593570

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PMID: 6321594



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