Regulatory T-Cells Mediate IFN-α-Induced Resistance against Antigen-Induced Arthritis.

Objective: CD4+FoxP3+CD25+ regulatory T-cells (Tregs) are important for preventing tissue destruction. Here, we investigate the role of Tregs for protection against experimental arthritis by IFN-α. Methods: Arthritis was triggered by intra-articular injection of methylated bovine serum albumin (mBSA) in wild-type mice, Foxp3DTReGFP+/- mice [allowing selective depletion of Tregs by diphtheria toxin (DT)] and CD4-Cre+/- IFNA1R flox/flox mice (devoid of IFNAR signaling in T-cells) earlier immunized with mBSA, with or without treatment with IFN-α or the indoleamine 2,3-dioxygenase (IDO)-metabolite kynurenine. Tregs were depleted in DT-treated Foxp3DTReGFP+/- mice and enumerated by FoxP3 staining. Suppressive capacity of FACS-sorted CD25+highCD4+ Tregs was tested in vivo by adoptive transfer and ex vivo in cocultures with antigen-stimulated CFSE-stained T-responder (CD25-CD4+) cells. IDO was inhibited by 1-methyl tryptophan. Results: Both control mice and mice devoid of IFNAR-signaling in T helper cells were protected from arthritis by IFN-α. Depletion of Tregs in the arthritis phase, but not at immunization, abolished the protective effect of IFN-α and kynurenine against arthritis. IFN-α increased the number of Tregs in ex vivo cultures upon antigen recall stimulation but not in naïve cells. IFN-α also increased the suppressive capacity of Tregs against mBSA-induced T-responder cell proliferation ex vivo and against arthritis when adoptively transferred. The increased suppressive activity against proliferation conferred by IFN-α was clearly reduced by in vivo inhibition of IDO at immunization, which also abolished the protective effect of IFN-α against arthritis. Conclusion: By activating IDO during antigen sensitization, IFN-α activates Tregs, which prevent arthritis triggered by antigen rechallenge. This is one way by which IFN-α suppresses inflammation.

Local but Not Systemic Administration of Uridine Prevents Development of Antigen-Induced Arthritis.

OBJECTIVE: Uridine has earlier been show to down modulate inflammation in models of lung inflammation. The aim of this study was to evaluate the anti-inflammatory effect of uridine in arthritis. METHODS: Arthritis was induced by intra-articular injection of mBSA in the knee of NMRI mice pre-immunized with mBSA. Uridine was either administered locally by direct injection into the knee joint or systemically. Systemic treatment included repeated injections or implantation of a pellet continuously releasing uridine during the entire experimental procedure. Anti-mBSA specific immune responses were determined by ELISA and cell proliferation and serum cytokine levels were determined by Luminex. Immunohistochemistry was used to identify cells, study expression of cytokines and adhesion molecules in the joint. RESULTS: Local administration of 25-100 mg/kg uridine at the time of arthritis onset clearly prevented development of joint inflammation. In contrast, systemic administration of uridine (max 1.5 mg uridine per day) did not prevent development of arthritis. Protection against arthritis by local administration of uridine did not affect the anti-mBSA specific immune response and did not prevent the rise in serum levels of pro-inflammatory cytokines associated with the triggering of arthritis. In contrast, local uridine treatment efficiently inhibited synovial expression of ICAM-1 and CD18, local cytokine production and recruitment of leukocytes to the synovium. CONCLUSION: Local, but not systemic administration of uridine efficiently prevented development of antigen-induced arthritis. The protective effect did not involve alteration of systemic immunity to mBSA but clearly involved inhibition of synovial expression of adhesion molecules, decreased TNF and IL-6 production and prevention of leukocyte extravasation. Further, uridine is a small, inexpensive molecule and may thus be a new therapeutic option to treat joint inflammation in RA.