Tim3⁺ Foxp3 ⁺ Treg Cells Are Potent Inhibitors of Effector T Cells and Are Suppressed in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disorder. Earlier studies have demonstrated that regulatory T (Treg) cells, the main cell type mediating immune tolerance, appeared to be enriched in the inflamed synovial tissues. It is still unclear why the Treg cells in RA patients are unable to limit exacerbated inflammation. Here, we found that the frequency of Tim3⁺Foxp3⁺ Treg cells, which were potent suppressors of proinflammatory responses, was downregulated in RA patients. Reduction in Tim3⁺Foxp3⁺ Treg frequency was correlated with increased RA disease activity. Furthermore, we observed that Tim3⁺Foxp3⁺ Tregs were expressed more interleukin (IL)-10 than Tim3⁻Foxp3⁺ Tregs. CD4⁺CD25⁺Tim3⁺ T cells had higher capability of inhibiting interferon (IFN)-γ and tumor necrosis factor (TNF)-α secretion from T cells and peripheral blood mononuclear cells (PBMCs) than CD4⁺CD25⁺Tim3⁻ T cells. Compared to that in healthy individuals, CD4⁺CD25⁺ T cells in RA patients were less potent in suppressing IFN-γ and TNF-α production from PBMCs. Blocking Tim3 on CD4⁺CD25⁺ T cells from healthy controls resulted in an elevation of IFN-γ and TNF-α production from PBMCs, suggesting that Tim3 expression on CD4⁺CD25⁺ T cells was required for optimal Treg function. However, this phenomenon was not observed in RA patients. In conclusion, our study suggested that the CD4⁺CD25⁺Foxp3⁺ Treg cells from RA patients demonstrated a reduction of Tim3 and were less functional than Treg cells from healthy controls in a Tim3-related manner.