Myeloperoxidase H₂O₂ halide system: cytotoxic effect on human blood leukocytes

Myeloperoxidase, H₂O₂, and a halide form a potent antimicrobial and cytotoxic system of the polymorphonuclear leukocyte. A cytotoxic effect of this system on human blood leukocytes is demonstrated, employing ⁵¹Cr release and dye exclusion assays. Cytotoxicity is dependent on enzymatically active myeloperoxidase, H₂O₂, or a peroxide generating enzyme system and either chloride or iodide. Cell damage is rapid, with maximal levels of ⁵¹Cr release occurring within 30 to 60 min. Approximately equal sensitivity to the peroxidase system is observed for polymorphonuclear leukocytes and mononuclear leukocytes. Since myeloperoxidase and H₂O₂ are released from polymorphonuclear leukocytes under certain conditions, such as during particle ingestion, it is suggested that peroxidase mediated leukocyte injury may be an important feature of the inflammatory response.