DETERMINANTS OF NEUTROPHIL HOCL GENERATION - LIGAND-DEPENDENT RESPONSES AND THE ROLE OF SURFACE-ADHESION

Neutrophil (PMN) generation of HOCl, an oxidant important in mediating tissue injury by PMN proteases, requires PMN production of H2O2 and t he catalytic activity of myeloperoxidase (MPG). Production of H2O2 and MPG release vary with the PMN activating ligand and are facilitated b y cellular adhesion. Leukotriene B-4, 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 suspe nded PMNs. Production of H2O2 was observed when fMLP, TNF-alpha, or HA IgG was added to PMNs adherent to bovine serum albumin (BSA)-coated we lls, but significant production of HOCl was observed only when HAIgG w as added to PMNs adherent to BSA-coated wells or when suspended PMNs t reated with TNF-or were allowed to settle in BSA-coated wells. Even gr eater production of both H2O2 and HOCl was observed when PMNs were inc ubated in wells coated with IgG (SAIgG). HOCl generation, when observe d, was accompanied by release of MPO. Nonadherent PMNs generated HOCl when treated with 50-100 ng/ml phorbol myristate acetate or when stimu lated with fMLP following treatment with cytochalasin B; PMN activatio n under these conditions was also associated with MPG release but HOCl production was much less efficient relative to PMNs stimulated by SAI gG. These studies indicate that surface adhesion and ligand-induced re sponses that facilitate release of myeloperoxidase and dismutation of superoxide to H2O2 are required for production of extracellularly rele ased HOCl; these responses are most efficiently utilized during PMN in teraction with SAIgG.