Neutrophils augment the release of TNFα from LPS-stimulated macrophages via hydrogen peroxide

We examined the effect of polymorphonuclear cells on the release of tumor necrosis factor (TNF alpha) in endotoxin-treated macrophages. Human peripheral blood neutrophils were co-cultured with mouse peritoneal macrophages stimulated with lipopolysaccharide (LPS). In a dose-dependent mariner FMLP (n-formyl-methionyl-leucyl-phenylalanine) augmented the release of TNF alpha by LPS-stimulated macrophages in the presence, but not in the absence, of neutrophils. The stimulating effect of neutrophils on macrophages was reversed by catalase, suggesting that the release of hydrogen peroxide from neutrophils was responsible for augmenting macrophage TNF alpha. Moreover, the direct addition of hydrogen peroxide to macrophages resulted in an increased secretion of TNF alpha. In addition, insertion of a porous membrane between the neutrophils and macrophages cancelled the effect, indicating that adherence of neutrophils may be necessary for augmentation of TNF alpha release. In summary, the data suggest that hydrogen peroxide released from stimulated neutrophils may act as an activator of macrophage function by increasing their release of TNF alpha. (C) 2000 Published by Elsevier Science B.V. All rights reserved.