Additive Effects of VDBP and 1,25(OH)2D3 on the Viability and Apoptosis of Rheumatoid Arthritis Synovial Fibroblasts.

Aim: This study is to investigate the additive effect of Vitamin D-binding protein (VDBP) and 1,25(OH)2D3 on the viability and apoptosis of synovial cells from patients with rheumatoid arthritis (RA). Methods: Synovial tissues and synovial fluid of patients with RA and osteoarthritis (OA) were collected. The expression of VDBP was analyzed with immunohistochemistry and ELISA. CCK-8 assay was applied to detect cell viability. Flow cytometry was used to analyze cell cycle and apoptosis. Results: Immunohistochemical results showed that the expression of VDBP in the synovium of RA patients was significantly lower than that of OA (P<0.05). Similarly, ELISA results presented a lower expression of VDBP in the synovial fluid of RA patients. The results of CCK-8 assay showed that both 1,25(OH)2D3 and VDBP significantly inhibited the viability of rheumatoid arthritis synovial fibroblasts (RASF) (P<0.05). The treatment with 1,25(OH)2D3+VDBP led to more significantly inhibited viability of RASF, compared with 1,25(OH)2D3 alone (P<0.05). The results of flow cytometry showed that 1,25(OH)2D3 and VDBP both promoted the apoptosis of RASF (P<0.05) and 1,25(OH)2D3+VDBP led to a higher proportion of RASF apoptosis, compared with 1,25(OH)2D3 alone (P<0.05). However, 1,25(OH)2D3 and VDBP had no significant effect on the cell cycle of RASF. Additionally, 1,25(OH)2D3 promoted the expression of VDBP in RASF, but not concentration-dependently. Conclusion: VDBP is reduced in the synovial tissue and synovial fluid of RA patients and can inhibit viability of RASF and promote the apoptosis of RASF. The 1,25(OH)2D3 can upregulate the expression of VDBP in RASF. Additionally, VDBP can enhance the effects of 1,25(OH)2D3 on viability and apoptosis of RASF.

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.