Soluble IL-6 receptor induces calcium flux and selectively modulates chemokine expression in human dermal fibroblasts

Truncated forms of cytokine receptors have been regarded as modulators of t he activity of their cognate ligands, In addition to inhibiting effects of their respective ligands, soluble receptors can also facilitate ligand-medi ated signaling. Several studies have demonstrated that exogenous IL-6 in as sociation with the soluble IL-6 receptor alpha (sIL-6R alpha) can activate cells expressing the gp130 signal transducer lacking the specific, membrane -bound IL-6R alpha. Since cell cultures of human dermal fibroblasts express high amounts of IL-6, we examined whether the addition of sIL-6R alpha in association with endogenous IL-6 would be sufficient to stimulate these cel ls via gp130, As an early rapid signal we analyzed changes in intracellular free calcium concentrations ([Ca2+](i)). Addition of sIL-6R alpha induced an acute and transient increase in cytosolic free calcium concentrations in a dose-dependent fashion. This Ca2+-signal was abolished when cells were p retreated with anti-IL-6 or anti-gp130 antibodies. Using flow cytometric an alysis we could demonstrate membrane-associated IL-6 and gp130, but not IL- 6R alpha on fibroblasts. We also analyzed MCP-1 and IL-8 expression as a re sponse involved in the more recently recognized chemoattractant functions o f fibroblasts, and found MCP-1 to be up-regulated, but not IL-8, These data suggest that sIL-6R alpha binds to cell-associated, endogenous IL-6 produc ed by fibroblasts and this complex then activates the cells via gp130. This pathway of fibroblast activation by sIL-6R alpha adds another dimension to the role of fibroblasts in the cytokine network.