Orbital fibroblast interleukin-6 gene expression and immunomodulation

Purpose: Orbital inflammation is common, but the mechanisms underlying leuk ocytic infiltration of orbital tissue are poorly understood. We studied hum an orbital fibroblast (OF) interleukin-6 (IL-6) gene expression in response to proinflammatory stimuli and the effects of dexamethasone (DEX) and cycl osporin A (CSA) on cytokine-stimulated OF IL-6 gene expression. Methods: Cultured OFs were left unstimulated or incubated with varying conc entrations of lipopolysaccharide (LPS), or recombinant (r) interleukin-1-be ta (rIL-1 beta), tumor necrosis factor-alpha (rTNF-alpha), or interferon-ga mma (rIFN-gamma) for 2, 4, 8, or 24 hours. OFs were also incubated with rIL -1 beta (0.2, 2.0, 20 ng/ml) alone or in the presence of DEX (10(-8), 10(-7 ), 10(-6) mol/l) or CSA (3, 30, 300 ng/ml) for 8 hours to determine the eff ects of these immunomodulating drugs on IL-6 expression. Northern blot anal yses were performed to determine OF IL-6 mRNA expression in response to var ying concentrations of these agents. Experiments were repeated four times o n different cell lines. Results: OFs lacked constitutive IL-6 gene expression. Substantial time- an d dose-dependent increases in steady-state IL-6 mRNA expression occurred by 4 hours of LPS or cytokine stimulation (rIL-1 beta>rTNF-alpha>LPS>rIFN-gam ma), peaked at 8 hours, and were maintained at 24 hours. DEX caused dose-de pendent inhibition of IL-1-induced IL-6 mRNA expression, while CSA potentia ted IL-1-induced OF IL-6 mRNA expression. Conclusions: OFs express IL-6 mRNA in response to proinflammatory stimuli. DEX is a potent inhibitor of OF IL-6 mRNA while CSA increases IL-1-induced OF IL-6 gene expression. These observations may in part explain the lack of CSA effectiveness in human orbital diseases that respond to corticosteroid s.