Tumor necrosis factor (TNF) is a 17,000-Da protein which is produced by mononuclear cells upon exposure to endotoxin. Increases in adherence, phagocytosis, hydrogen peroxide release, and lysozyme secretion have been demonstrated after prolonged incubation of human neutrophils with TNF. In this study, the ability of highly purified recombinant human TNF to modulate neutrophil responses to soluble stimuli was evaluated. Tumor necrosis factor alone (0.1 to 10,000 units/ml) failed to induce neutrophil superoxide anion (O2-) production, granule release, or aggregation when incubated for up to 25 min at 37 degrees C. TNF did, however, stimulate a significant time-, dose-, and temperature-dependent increase in neutrophil F-actin content. Although exposure of neutrophils to TNF alone caused no superoxide anion production, it enhanced the O2- production in response to the chemotactic peptide, f-methionyl-leucyl-phenylalanine (FMLP) or the tumor promotor, phorbol myristate acetate, by as much as 278%. The enhancement was time-, dose-, and temperature-dependent and was due to a more rapid initial rate of O2- production. The TNF enhancement of FMLP-induced O2- production was blocked when an anti-TNF monoclonal antibody 241-1H11, is present during the preincubation period. TNF preincubation also enhanced FMLP-induced lysozyme release, but had no effect on aggregation and actin polymerization by FMLP. The kinetics of NADPH oxidase activation by arachidonic acid was unaltered by TNF. These results indicate that brief exposures to recombinant human TNF are able to enhance or prime the neutrophil oxidative burst in response to a second stimulus.

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