PEROXIDASE-MEDIATED OXYGENATION AND MICROBICIDAL ACTIVITY

It is known that a peroxidase, H2O2, and a halide form a "cytotoxic triad." As a result of the interactions of the components of the triad, reactive oxygen intermediates (ROI) are formed that help to destroy various invading pathogens including Candida. The present study was undertaken to determine if equivalent units of peroxidase induced equivalent levels of macrophage-mediated killing of Candida. Murine peritoneal macrophages were exposed to various concentrations of eosinophil peroxidase (EPO), myeloperoxidase (MPO), and horseradish peroxidase (HRP). Luminol-dependent chemiluminescence studies showed that equivalent units of peroxidase, as determined by oxidation of guaiacol, demonstrated a hierarchical pattern of ROI production. Macrophage phagocytosis and candidicidal activity, as measured by a fluorescence acridine orange assay, also demonstrated the same hierarchical pattern of EPO > MPO > HRP. Therefore, enzymatically equivalent peroxidases do not demonstrate equivalent candidicidal activity. These data indicate a distinct order of peroxidases relative to their ability to stimulate chemiluminescence and macrophage-mediated killing.