Determinants of neutrophil HOCI generation: ligand-dependent responses and the role of surface adhesion

Abstract

Neutrophil (PMN) generation of HOCl, an oxidant important in mediating tissue injury by PMN proteases, requires PMN production of H2O2 and the catalytic activity of myeloperoxidase (MPO). Production of H2O2 and MPO release vary with the PMN activating ligand and are facilitated by cellular adhesion. Leukotriene B4, platelet-activating factor, heat-aggregated immunoglobulin G (HAIgG), tumor necrosis factor alpha (TNF-alpha), and f-Met-Leu-Phe (fMLP) all triggered significant superoxide production but negligible H2O2 or HOCl generation when added to suspended PMNs. Production of H2O2 was observed when fMLP, TNF-alpha, or HAIgG was added to PMNs adherent to bovine serum albumin (BSA)-coated wells, but significant production of HOCl was observed only when HAIgG was added to PMNs adherent to BSA-coated wells or when suspended PMNs treated with TNF-alpha were allowed to settle in BSA-coated wells. Even greater production of both H2O2 and HOCl was observed when PMNs were incubated in wells coated with IgG (SAIgG). HOCl generation, when observed, was accompanied by release of MPO. Nonadherent PMNs generated HOCl when treated with 50-100 ng/ml phorbol myristate acetate or when stimulated with fMLP following treatment with cytochalasin B; PMN activation under these conditions was also associated with MPO release but HOCl production was much less efficient relative to PMNs stimulated by SAIgG. These studies indicate that surface adhesion and ligand-induced responses that facilitate release of myeloperoxidase and dismutation of superoxide to H2O2 are required for production of extracellularly released HOCl; these responses are most efficiently utilized during PMN interaction with SAIgG.