IL-6-soluble IL-6 receptor complex inhibits the proliferation of dermal fibroblasts

A number of investigators has reported that there is increased production of interleukin-6 (IL-6) by fibroblasts and monocytes from the patients with systemic sclerosis (SS). However, the precise role of IL-6 in the pathogenesis of SS remains unclear. On the basis of our previous study showing that the complex of IL-6 and soluble IL-6 receptor (sIL-6R) could induce synovial fibroblast proliferation, we examined whether the IL-6-sL-6R complex could induce the proliferation of normal dermal fibroblastic cells (DF). IL-6 suppressed DF proliferation, and, in the presence of sIL-6R, dose-dependently showed much stronger suppressive effects on DF proliferation. This suppression was completely blocked by either anti-IL-6 or anti-sIL-6R antibody. Furthermore, the IL-6-sIL-6R complex significantly suppressed IL-1 beta-, TNF alpha- and PDGF-AA-induced DF proliferation. These lines of evidence suggest that the IL-6-sIL-6R complex may have potential as a useful agent for the treatment of SS.