Purpose: Orbital inflammation is common, but the mechanisms underlying leukocytic infiltration of orbital tissue are poorly understood. We studied human orbital fibroblast (OF) interleukin-6 (IL-6) gene expression in response to proinflammatory stimuli and the effects of dexamethasone (DEX) and cyclosporin A (CSA) on cytokine-stimulated OF IL-6 gene expression.
Methods: Cultured OFs were left unstimulated or incubated with varying concentrations of lipopolysaccharide (LPS), or recombinant (r) interleukin-1-beta (rIL-1beta), tumor necrosis factor-alpha (rTNF-alpha), or interferon-gamma (rIFN-gamma) for 2, 4, 8, or 24 hours. OFs were also incubated with rIL-1beta (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 effects of these immunomodulating drugs on IL-6 expression. Northern blot analyses were performed to determine OF IL-6 mRNA expression in response to varying concentrations of these agents. Experiments were repeated four times on different cell lines.
Results: OFs lacked constitutive IL-6 gene expression. Substantial time- and dose-dependent increases in steady-state IL-6 mRNA expression occurred by 4 hours of LPS or cytokine stimulation (rIL-1beta>rTNF-alpha(>LPS>rIFN-gamma), peaked at 8 hours, and were maintained at 24 hours. DEX caused dose-dependent inhibition of IL-1-induced IL-6 mRNA expression, while CSA potentiated 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 corticosteroids.