ICOS+ T helper 2 cells promote the pulmonary fibrosis in systemic sclerosis

Interstitial lung disease (ILD) is the most frequent complication of systemic sclerosis (SSc), associated with a poor prognosis and limited treatments. T helper 2 (Th2) cells play a key role in SSc pathogenesis, with T cell inducible co-stimulator (ICOS) involved in Th2 differentiation and IL-4 expression. However, the specific role of ICOS+ Th2 cells in SSc-ILD remains unclear. Peripheral blood mononuclear cells (PBMCs) from SSc patients and healthy controls were analyzed via mass cytometry (CyTOF). The CD4+CXCR5−ICOS+IL-4+ T cell subset was further characterized using flow cytometry. In vitro, human lung fibroblasts were co-cultured with differentiated CD4+ICOS+IL-4+ cells, and fibrotic gene expression was measured. An in vivo SSc-ILD model was induced via bleomycin instillation, and the frequency of CD4+CXCR5−ICOS+IL-4+ cells was assessed in the lung. Functional contributions were evaluated by transferring CD4+ICOS+IL-4+ cells into Rag2−/− mice, followed by histological analysis of lung inflammation and fibrosis. CyTOF identified a CD4+CCR4+ICOS+ T cell subset significantly increased in SSc-ILD patients, defined as ICOS+ Th2 cells by the absence of CXCR5, CXCR3, and CCR6 and the presence of CCR4. Elevated CD4+CXCR5−ICOS+IL-4+ T cells were confirmed in SSc-ILD patient PBMCs and in the lungs of bleomycin-treated mice. Functionally, ICOS+ Th2 cells induced high expression of Vimentin, Fibronectin, and α-SMA in fibroblasts when co-cultured with TGF-β. Adoptive transfer of ICOS+ Th2 cells into Rag2−/− mice caused lung inflammation and upregulated fibrosis-related genes, including α-SMA, Col1a1, Col1a2, and Col3a1. This study identifies ICOS+ Th2 cells as a key subset contributing to SSc-ILD inflammation and fibrosis, highlighting their potential as therapeutic targets.