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

Neutrophil (PMN) generation of HOCI, an oxidant important in mediating tissue injury by PMN proteases, requires PMN production of H 2 O 2 and the catalytic activity of myeloperoxidase (MPO). Production of H 2 O 2 and MPO release vary with the PMN activating ligand and are facilitated by cellular adhesion. Leukotriene B 4 , platelet‐activating factor, heat‐aggregated immunoglobulin G (HAIgG), tumor necrosis factor α (TNF‐ α ), and f‐Met‐Leu‐Phe (fMLP) all triggered significant superoxide production but negligible H 2 O 2 or HOCI generation when added to suspended PMNs. Production of H 2 O 2 was observed when fMLP, TNF‐ α , or HAIgG was added to PMNs adherent to bovine serum albumin (BSA)‐coated wells, but significant production of HOCI was observed only when HAIgG was added to PMNs adherent to BSA‐coated wells or when suspended PMNs treated with TNF‐ α were allowed to settle in BSA‐coated wells. Even greater production of both H 2 O 2 and HOCI was observed when PMNs were incubated in wells coated with IgG (SAIgG). HOCI generation, when observed, was accompanied by release of MPO. Nonadherent PMNs generated HOCI 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 HOCI 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 H 2 O 2 are required for production of extracellularly released HOCI; these responses are most efficiently utilized during PMN interaction with SAIgG. J. Leukoc. Biol. 56: 654–660; 1994.