EOSINOPHIL PEROXIDASE-DEPENDENT HYDROXYL RADICAL GENERATION BY HUMAN EOSINOPHILS

Eosinophil production of superoxide (O-2-radical anion) and hydrogen p eroxide (H2O2) is important in host defense. The present study assesse d the potential of eosinophils to generate another potent cytotoxic sp ecies, the hydroxyl radical ((OH)-O-.). (OH)-O-. formation by phorbol myristate acetate (PMA)-stimulated eosinophils was demonstrated using an alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone/ethanol spin trappin g system. Additionally, (OH)-O-. was spin trapped following the additi on of purified eosinophil peroxidase (EPO) to a cell-free O-2-radical anion/H2O2 generating systems. Effects of superoxide dismutase, catala se, azide, aminotriazole, chloride-depleted buffer, and extensive meta l chelation were consistent with (OH)-O-. formation via the reaction o f O-2-radical anion and EPO-generated hypohalous acid. Under chloride- depleted conditions, physiologic concentrations of Br- increased (OH)- O-. formation by both PMA-stimulated eosinophils and the cell-free EPO system. Physiologic concentrations of SCN-, however, did not increase (OH)-O-. formation, and in the presence of both Br- and SCN-, (OH)-O- . formation was similar to SCN- only. Eosinophils appear to form (OH)- O-. via an EPO-dependent mechanism, the magnitude of which varies with the availability of various EPO substrates. Given the highly reactive nature of this radical and the ability of EPO to adhere to cell membr anes, even small amounts of (OH)-O-. formed at such sites could contri bute to eosinophil-mediated cytotoxicity.