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 iii combination on IL-8 production by HGF. IL-1 beta, tumor necrosis factor-alpha (TNF-alpha), Interferon-gamma (IFN-gamma), IL-6, and IL-8 were used as stimulants. HGF secreted IL-8 in a dose-dependent manner after stimulation with either IL-1 beta or TNF-alpha, but not with IFN-gamma or IL-6. Furthermore, IL-8 itself did not affect IL-8 mRNA accumulation in HGF in an autocrine manner, The combination of IL-1 beta and TNF-alpha synergistically enhanced the secretion of IL-8, whereas IFN-gamma suppressed IL-8 secretion by IL-1 beta- or TNF-alpha-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 my the inhibition of PGE(2) synthesis with indomethacin, indicating that endogenous PGE(2) 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-1 beta and TNF-alpha, and suggest that these stimulatory effects are down-regulated by IFN-gamma at the transcriptional let ei through PGE(2)-independent pathways. Thus, neutrophil-mediated processes in periodontal disease may be regulated in part by HGF in the cytokine network of immuno-participant cells.