The mechanisms involved in the physiopathology of systemic sclerosis (SSc) are not fully understood, particularly the pattern of cytokine expression in the skin of SSc patients. These cytokines are known to play a central role in the regulation of numerous inflammatory diseases and, among them, IL-34 is the only cytokine which has been found to be down-regulated in other skin inflammatory disorders such psoriasis or atopic dermatitis. IL-34 has been described as an immunosuppressive cytokine, and our preliminary results show that IL-34 is active on fibroblasts, a key cell that undergoes dysfunction in SSc. Thus, we are willing to explore its expression profile in the skin of SSc patients and its potential role in the physiopathology of the disease. For this study, we will analyze IL-34 mRNA levels in the skin and the plasma of SSc patients by comparison to healthy patients. Thirty patients will be included in the Internal Medicine Unit of the CHU de Poitiers during a single visit, in the frame of their medical follow-up, to collect two skin biopsies and 5 ml of blood after obtaining their informed consent. The expression of IL-34 will also be investigated at the protein level by immunostaining on skin sections and by ELISA (skin protein lysates and plasma). Moreover, the expression of other proinflammatory cytokines will be investigated both at the mRNA and protein levels.
By contrast to other proinflammatory cytokines which are found up-regulated in the skin of patients with psoriasis, atopic dermatitis or systemic sclerosis, IL-34 is the only cytokine that undergoes down-regulation. This finding is interesting regarding the description of IL-34 as an immunosuppressive cytokine. In this study, the expression and the role of interleukin-34 (IL-34) will be investigated in the physiopathology of systemic sclerosis.