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 o xygen 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-m ediated killing of Candida. Murine peritoneal macrophages were exposed to V arious concentrations of eosinophil peroxidase (EPO), myeloperoxidase (MPO) , and horseradish peroxidase (HRP). Luminol-dependent chemiluminescence stu dies showed that equivalent units of peroxidase, as determined by oxidation of guaiacol, demonstrated a hierarchical pattern of ROI production. Macrop hage phagocytosis and candidicidal activity, as measured by a fluorescence acridine orange assay, also demonstrated the same hierarchical pattern of E PO > MPO > HRP. Therefore, enzymatically equivalent peroxidases do not demo nstrate equivalent candidicidal activity. These data indicate a distinct or der of peroxidases relative to their ability to stimulate chemiluminescence and macrophage-mediated killing.