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Oxidative mechanisms of monocyte-mediated cytotoxicity
Abstract:
Human monocytes stimulated with phorbol myristate acetate were able to rapidly destroy autologous erythrocyte targets. Monocyte-mediated cytotoxicity was related to phorbol myristate acetate concentration and monocyte number. Purified preparations of lymphocytes were incapable of mediating erythrocyte lysis in this system. The ability of phorbol myristate acetate-stimulated monocytes to lyse erythrocyte targets was markedly impaired by catalase or superoxide dismutase but not by heat-inactivated enzymes or albumin. Despite a simultaneous requirement for superoxide anion and hydrogen peroxide in the cytotoxic event, a variety of hydroxyl radical and singlet oxygen scavengers did not effect cytolysis. However, tryptophan significantly inhibited cytotoxicity. The myeloperoxidase inhibitor cyanide enhanced erythrocyte destruction, whereas azide reduced it modestly. The inability of cyanide to reduce cytotoxicity coupled with the protective effect of superoxide dismutase suggests that cytotoxicity is independent of the classic myeloperoxidase system. We conclude that monocytes, stimulated with phorbol myristate acetate, generate superoxide anion and hydrogen peroxide, which together play an integral role in this cytotoxic mechanism.
Insights
Phorbol myristate acetate-stimulated monocytes rapidly destroy red blood cells. This monocyte cytotoxicity relies on superoxide anion and hydrogen peroxide, not the myeloperoxidase system.
Area of Science:
- Immunology
- Cell Biology
Background:
- Human monocytes can eliminate autologous red blood cells.
- This monocyte-mediated cytotoxicity is dose-dependent on phorbol myristate acetate and monocyte concentration.
Purpose of the Study:
- To investigate the mechanism of monocyte-mediated cytotoxicity against erythrocyte targets.
- To determine the role of reactive oxygen species in this cytotoxic process.
Main Methods:
- Monocytes were stimulated with phorbol myristate acetate (PMA).
- Cytotoxicity was assessed by erythrocyte lysis.
- The effects of various scavengers and inhibitors were evaluated.
Main Results:
- PMA-stimulated monocytes exhibited rapid erythrocyte lysis.
- Cytotoxicity was impaired by catalase and superoxide dismutase, indicating a role for hydrogen peroxide and superoxide anion.
- Hydroxyl radical and singlet oxygen scavengers had no effect, while tryptophan inhibited cytotoxicity.
- Myeloperoxidase inhibitors (cyanide, azide) showed varied effects, suggesting independence from the classic myeloperoxidase system.
Conclusions:
- Monocyte-mediated erythrocyte lysis induced by PMA involves superoxide anion and hydrogen peroxide.
- This cytotoxic mechanism is distinct from the classical myeloperoxidase pathway.