Th17 cells and IL-17 promote the skin and lung inflammation and fibrosis process in a bleomycin-induced murine model of systemic sclerosis.

Objectives: Systemic sclerosis (SSc) is characterised by fibrosis of the skin and internal organs, such as the lungs. Enhanced Th17 responses are associated with skin fibrosis in patients with SSc, however, whether they are associated with lung fibrosis has not been clarified. This study aimed to investigate the potential association of Th17 responses with the skin and pulmonary fibrosis as well as the potential mechanisms in a mouse bleomycin (BLM) model of SSc.

Methods: BALB/c mice were injected subcutaneously with phosphate buffered saline (PBS) (control) or BLM for 28 days and the skin and pulmonary inflammation and fibrosis were characterized by histology. The percentages of circulating, skin and pulmonary infiltrating Th17 cells and the contents of collagen in mice were analysed. The levels of RORγt, IL-17A, IL-6 and TGF-β1 mRNA transcripts in the skin and lungs were determined by quantitative RTPCR and the levels of serum IL-17A, IL-6 and TGF-β1 were determined by ELISA. Furthermore, the effect of rIL-17A on the proliferation of pulmonary fibroblasts and their cytokine expression was analysed. The potential association of Th17 responses with the severity of skin and lung fibrosis was analysed.

Results: In comparison with the control mice, significantly increased skin and pulmonary inflammation and fibrosis and higher levels of hydroxyproline were detected in the BLM mice. Significantly higher frequency of circulating, skin and lung infiltrating Th17 cells and higher levels of serum, skin and lung IL-17A, TGF-β1, IL-6 and RORγt were detected in the BLM mice. The concentrations of serum IL-17A were correlated positively with the percentages of Th17 cells and the contents of skin hydroxyproline in the BLM mice. The levels of IL-17A expression were positively correlated with the skin and lung inflammatory scores as well as the skin fibrosis in the BLM mice. In addition, IL-17A significantly enhanced pulmonary fibroblast proliferation and their type I collagen, TGF-β and IL-6 expression in vitro, which were attenuated by treatment with anti-IL-17A.

Conclusions: Our results indicate that Th17 cells participate in the pathogenesis of skin and lung fibrosis by enhancing fibroblast proliferation and cytokine production in a mouse BLM model of SSc.