Increased frequency of Th17 cells in systemic sclerosis is related to disease activity and collagen overproduction

INTRODUCTION Although immune dysfunction plays a role in the pathogenesis of systemic sclerosis (SSc), involvement of T helper 17 (Th17) and T regulatory (Treg) cells remains unclear. We aimed to investigate the presence of Th17 and Treg cells in SSc patients and the role of Th17 cells in collagen production in SSc fibroblasts. METHODS We analyzed inflammatory cell profiles in the skin of 13 SSc patients by immunohistochemistry, the percentage of Th17 and Treg cells in peripheral blood mononuclear cells (PBMCs) of 45 SSc patients and 24 healthy controls by flow cytometry, gene expression in PBMCs by real-time reverse transcription-polymerase chain reaction and interleukin-17 (IL-17) in sera and culture supernatants by enzyme-linked immunosorbent assay. We also investigated the effect of Th17 cell-derived IL-17 on fibroblast growth and collagen production. RESULTS Infiltration of inflammatory cells including IL-17⁺ and Foxp3⁺ lymphocytes was detected in the skin of patients with early SSc. The percentages of circulating Th17 cells and IL-17 production were elevated in samples from patients with active SSc, whereas the percentage of circulating Treg cells was not affected. The number of Th17 cells was closely related to disease activity. IL-17 from SSc patients promoted fibroblast growth and collagen production, whereas IL-17 neutralizing antibody effectively blocked collagen production. CONCLUSION SSc progression might be linked to expansion of circulating Th17 cells and increased infiltration of IL-17⁺ cells in skin. Th17-derived IL-17 is involved in fibroblast growth and collagen production. IL-17 blocking antibody may be a useful tool for intervention in the fibrotic course of SSc.