Cytokine-dependent synergistic regulation of interleukin-8 production from human gingival fibroblasts

Human gingival fibroblasts (HGF) may have an important role in the orchestration of immuno-participant cells infiltrating the gingiva in response to continuously recurring bacterial infection. To examine the cytokine network regulating HGF-derived interleukin (IL)-8, a potent neutrophil chemotactic cytokine, we analyzed the effects of inflammatory cytokines alone and in combination on IL-8 production by HGF. IL-1β, tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), IL-6, and IL-8 were used as stimulants. HGF secreted IL-8 in a dose-dependent manner after stimulation with either IL-1β or TNF-α, but not with IFN-γ or IL-6. Furthermore, IL-8 itself did not affect IL-8 mRNA accumulation in HGF in an autocrine manner. The combination of IL-1β and TNF-α synergistically enhanced the secretion of IL-8, whereas IFN-γ suppressed IL-8 secretion by IL-1β- or TNF-α-stimulated HGF. These effects were also observed at each level of IL-8 mRNA expression in HGF. IL-8 secretion by cytokine-stimulated HGF was not influenced by the inhibition of PGE₂ synthesis with indomethacin, indicating that endogenous PGE₂ was not involved in IL-8 production by HGF. These results indicate that IL-8 production by HGF is synergistically stimulated by specific cytokines, IL-1β and TNF-α, and suggest that these stimulatory effects are down-regulated by IFN-γ at the transcriptional level through PGE₂-independent pathways. Thus, neutrophil-mediated processes in periodontal disease may be regulated in part by HGF in the cytokine network of immuno-participant cells.