LAUSR

OBJECTIVES Rheumatoid arthritis (RA) is an autoimmune disease characterized by destructive polyarthritis. CD4+ T cells are pivotal to its pathogenesis, and our previous study revealed the expression of fibroblast growth factor receptor 1 (FGFR1) is modulated by methotrexate treatment in CD4+ T cells of RA patients; however, the roles of FGFR1 in CD4+ T cells in the pathogenesis of RA is unclear. Therefore, in this study, we aimed to characterize FGFR1-positive CD4+ T cells in RA patients. METHODS The abundance of FGFR1-positive CD4+ T cells in peripheral blood and synovium was determined. Single-cell RNA sequencing (scRNA-seq) was performed on synovial CD4+ T cells to characterize FGFR1-positive cells. In addition, T cell activation status and cytokine production were determined using flow cytometry. RESULTS The percentage of FGFR1-positive CD4+ T cells in the peripheral blood was higher in RA patients than in healthy controls (P= 0.0035). They were also present in the synovium of active RA patients. The results of scRNA-seq revealed that peripheral T helper (Tph) cells preferentially expressed FGFR1. Additionally, these FGFR1-positive Tph cells displayed a terminal effector cell phenotype. Consistent with this finding, FGFR1-positive CD4+ T cells in peripheral blood expressed interleukin-21 and interferon-γ. CONCLUSION Our study provides evidence that FGFR1 marks terminal effector Tph cells in patients with RA.