Polymorphonuclear leukocytes (PMN) have been identified as important sources of various proinflammatory cytokines. Since Interferon-gamma (IFN-gamma) is one of the activating factors of PMN, we have examined its effect on PMN-derived cytokine production. Recently, we demonstrated that IFN-gamma inhibits the release of IL-8 by PMN stimulated for 2 with different agonists. In this report, we show that the IFN-gamma-dependent inhibition of IL-8 release by PMN stimulated with lipopolysaccharide (LPS), tumor necrosis factor (TNF), and/or interleukin-1 beta (IL-1 beta), but not with Y-IgG, is a transient phenomenon. Indeed, PMN stimulated in the presence of IFN-gamma for 18 hr demonstrated an enhanced expression of IL-8 antigen in cell-free supernatants compared with stimuli alone. This enhanced accumulation of IL-8 partially reflected changes at the level of cell-associated versus cell-secreted IL-8 as PMN incubated with IFN-gamma secreted significantly more IL-8, relative to untreated cells. Unlike IL-8, the LPS-stimulated production of TNF and IL-1 beta, as well as the TNF-stimulated production of IL-1 beta, was markedly enhanced by IFN-gamma over the entire incubation period (up to 18 hr). Addition of anti-TNF and anti-IL-1 beta antibodies to IFN-gamma plus LPS-treated PMN indicated that the LPS-induced production of endogenous TNF and IL-1 beta, which was further potentiated by IFN-gamma pretreatment, mediated in autocrine fashion the enhanced LPS-induced IL-8 accumulation observed at 18 hr. Furthermore, as shown by Northern blot analysis, all the effects of IFN-gamma on LPS-stimulated PMN were paralleled by changes at the level of TNF, IL-1 beta, and IL-8 mRNA expression. Taken together, these findings identify novel biological actions of IFN-gamma as a modulator of the acute inflammatory response.