IL-1 receptor blockade skews inflammation towards Th2 in a mouse model of systemic sclerosis

The interleukin (IL)-1 family of cytokines is strongly associated with systemic sclerosis (SSc) and pulmonary involvement, but the molecular mechanisms are poorly understood. The aim of this study was to assess the role of IL-1α and IL-1β in pulmonary vascular and interstitial remodelling in a mouse model of SSc. IL-1α and IL-1β were localised in lungs of SSc patients9 and in the Fra-2 transgenic (TG) mouse model of SSc. Lung function, hemodynamic parameters and pulmonary inflammation were measured in Fra-2 TG mice with or without 8 weeks of treatment with the IL-1 receptor antagonist anakinra (25 mg·kg −1 ·day −1 ). Direct effects of IL-1 on pulmonary arterial smooth muscle cells (PASMC) and parenchymal fibroblasts (PF) were investigated in vitro . Fra-2 TG mice exhibited increased collagen deposition in the lung, restrictive lung function and enhanced muscularisation of the vasculature with concomitant pulmonary hypertension reminiscent of the changes in SSc patients. IL-1α and IL-1β immunoreactivity was increased in Fra-2 TG mice and in patients with SSc. IL-1 stimulation reduced collagen expression in PASMC and PF via distinct signalling pathways. Blocking IL-1 signalling in Fra-2 TG worsened pulmonary fibrosis and restriction, enhanced Th2 inflammation and increased the number of pro-fibrotic, alternatively activated macrophages. Our data suggest that blocking IL-signalling as currently investigated in several clinical studies might aggravate pulmonary fibrosis in specific patient subsets due to Th2 skewing of immune responses and formation of alternatively activated pro-fibrogenic macrophages.