Th1 Polarization of JIA Synovial Fluid T Cells

We sought to determine the immunophenotype of joint-infiltrating CD4+ T cells as well as the stability of Tregs in oligo JIA. This was done through the use of flow cytometry, bulk and single-cell RNA sequencing, DNA methylation studies, and Treg suppression assays. We show that CD4+ T cells in SF, including Tregs, are predominantly Th1-polarized. Disease extension is associated with a greater proportion of IFN?-expressing CD4+ T cells in the joint. Importantly, Th1-skewed SF Tregs in oligo JIA maintain Treg identity and suppressive functionality. Our findings suggest that inhibiting the Th1 pathway and enhancing Treg function may be key in controlling arthritic flares in oligo JIA.