Knee osteoarthritis (OA) is the most common cause of musculoskeletal pain and disability in the knee. Though traditionally thought a mechanical wear-and-tear disease, in recent years, knee OA as a low-grade, chronic inflammatory disease has been increasingly recognized. In this study, we examined the Treg responses in non-obese knee OA patients at different stages. Significantly elevated frequencies of CD4(+)CD25(+)Foxp3(+) Tregs were found in OA patients, while on the other hand, lower IL-10 secretion from Tregs in OA patients was observed. Importantly, this decrease in IL-10 was associated with reduced Tim-3 expression on Tregs. Although both Tim-3(-) and Tim3(+) Tregs could secrete IL-10, the majority of IL-10 was observed in Tim-3(+) Tregs. Reduction of Tim-3(+) Tregs in OA patients resulted in less IL-10-producing Tregs. Interestingly, the OA patients in more advanced stages showed further reductions in IL-10 and Tim-3 expression. In conclusion, our results revealed an immunoregulatory disorder in OA independent of obesity, and demonstrated a potential mechanism in establishing the proinflammatory status of OA patients.

Rheumatoid arthritis (RA) is characterized by a chronic inflammatory process that targets the synovial lining of diarthrodial joints. TIM-3 plays a key role in the negative regulation of the immune response. In this study, we investigated the expression of TIM-3 on CD4+ and CD8+ T cells from systemic (peripheral blood) and local (synovial fluid) perspectives of RA. Level of TIM-3+ cells from peripheral blood and synovial fluid of patients as well as peripheral blood of healthy controls was measured by flow cytometry. Results showed that TIM-3 expression was significantly increased in both CD4+ and CD8+ T cells in the peripheral blood of RA (p < 0.001 and p < 0.001, respectively). Furthermore, patients revealed even higher expression of TIM-3 in CD4+ and CD8+ T cells in synovial fluid than in peripheral blood. When comparing TIM-3 level with the severity of RA, we identified that the percentage of TIM-3 on both peripheral CD4+ and peripheral CD8+ T cells was negatively correlated with disease activity score 28 (DAS28) of the patients. Similarly, TIM-3 on synovial fluid CD4+ and CD8+ T cells also revealed inverse correlation with DAS28 of the cases. Our data demonstrate a negative correlation between TIM-3 and the disease progression of RA.

Level IV, retrospective case series.