Growth Factors , Cytokines , and Cell Cycle Molecules Blockade of Interleukin-6 Receptor Alleviates Disease in Mouse Model of Scleroderma

Activation of fibroblasts by interleukin-6 (IL-6) is implicated in the pathogenesis of scleroderma, suggesting that the inhibition of fibroblast activation may be a promising scleroderma treatment. In this study, we used an IL-6 blocking antibody (Ab) and Il-6 knockout (Il-6KO) mice to examine the role of IL-6 in the bleomycin (BLM)-induced mouse model of scleroderma. BLM was administered to C57BL/6 and Il-6KO mice to induce dermal sclerosis. BLM-treated and control phosphate-buffered saline-treated mice were treated with anti-mouse IL-6 receptor monoclonal Ab (MR161). Disease severity was evaluated by measuring dermal thickness and skin hardness, by counting the numbers of -smooth muscle actin-positive cells and mast cells, and by examining the cutaneous draining lymph nodes. C57BL/6 mice with BLM induced scleroderma had elevated serum IL-6 levels and more severe dermal sclerosis than Il-6KO mice. Weekly administration of MR16-1, but not control Ab, prevented and improved dermal sclerosis, and also attenuated swelling of the draining lymph nodes. MR16-1 suppressed -smooth muscle actin induction in IL-6–stimulated Il-6KO fibroblasts. Our results indicate that IL-6 contributes to BLM induced dermal sclerosis and that IL-6 receptor–specific monoclonal Ab may improve the symptoms of scleroderma by suppressing fibroblast activation. (Am J Pathol 2012, 180:165–176; DOI: 10.1016/j.ajpath.2011.09.013) Patients with scleroderma frequently experience broad area skin sclerosis and internal organ involvement including pulmonary fibrosis, esophageal dysfunction, pulmonary arterial hypertension, renal crisis, and heart failure. These symptoms dramatically affect the prognosis for scleroderma patients. Autoaggressive immunological activation and continuous activation of fibroblasts are the key components of scleroderma, yet the mechanisms underlying these are incompletely understood. Several lines of evidence indicate that interleukin (IL)-6 contributes to the disease process in scleroderma. Serum IL-2, IL-4, IL-6, and tumor necrosis factor levels are elevated in scleroderma. Increased serum IL-6 levels are also observed in both scleroderma mouse models: the bleomycin (BLM)-induced scleroderma mouse and the type 1 tight-skin mouse (Tsk1/ ). At the cellular level, IL-6–producing T helper type 2 clones contribute to anti-DNA topoisomerase I autoantibody, a key autoantibody in scleroderma. The point of action of IL-6 in scleroderma remains controversial, with some evidence suggesting the final maturation step of B cells and/or activation of fibroblasts. Thus, although the specific function of IL-6 in the pathogenesis of scleroderma remains unclear, there is ample evidence that inhibition of IL-6–mediated signaling might be a route to better treatment for scleroderma. In this study, we used the BLM-induced scleroderma mouse model to demonstrate the importance of IL-6 in pathogenesis of scleroderma and to evaluate the effect of anti-mouse IL-6 receptor monoclonal antibody. We have examined whether MR16-1 acts directly on dermal fibroblasts by investigating the induction of myofibroblasts in vitro. We also examined the tissue of scleroderma patients treated with tocilizumab, a humanized monoclonal antibody (Ab) against the IL-6 receptor used to treat rheumatoid arthritis or Castleman’s disease. Patients