Objective: This study explored the role of IL-35 in CD4+ T lymphocyte and human skin fibroblast (HSF) activity and cytokine levels in systemic sclerosis.
Methods: Blood and skin biopsies were collected from 41 patients and 39 healthy controls to assess CD4+ T lymphocytes and IL-35-related factors. CD4+ T lymphocytes were co-cultured with HSFs, recombinant human IL-35 and IL-35 mAb to evaluate the cell viability, activation of CD4+ T lymphocytes and HSF cells.
Results: The proportion of blood Th1/Th2 was lower and Th17/Treg was higher in patients than in controls (P < 0.05). IL-35 and IL-17A levels were higher and IFN-γ, IL-10 and TGF-β levels were lower in patients than in controls. IL-17A, forkhead box P3, TGF-β1 and collagen type I (COL-1) mRNA and phospho (p)-signal transducer and activator of transcription (STAT) 1 and p-STAT4 were higher in skin tissues from patients than in those from controls (P < 0.05). IL-6 levels were higher, whereas IL-10 levels were lower in cell culture supernatants. α-Smooth muscle actin (α-SMA) and COL-1 proteins and Ki67 positivity were higher in CD4+ T + HSF cells from patients than in those from controls. Recombinant human IL-35 treatment inhibited proliferation (P < 0.001), but increased IL-10 and decreased IL-17A, α-SMA and COL-1 secretion into the conditioned medium of CD4+ T lymphocytes + HSFs from patients compared with those from controls. IL-35 mAb blocked the effects of IL-35 in CD4+ T + HSF cells (P < 0.05).
Conclusions: IL-35 plays an inhibitory role in CD4+ T lymphocyte proliferation but induces Treg cell differentiation by STAT1 signalling activation, HSF proliferation and collagen expression in systemic sclerosis.
Keywords: CD4+ T lymphocytes; human skin fibroblast (HSF); interleukin-35; regulatory T cells; systemic sclerosis.
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