Elevated expression of interleukin‐7 receptor in inflamed joints mediates interleukin‐7–induced immune activation in rheumatoid arthritis

Abstract

Objective: To evaluate the expression and functional ability of the high‐affinity interleukin‐7 receptor (IL‐7Rα) in patients with rheumatoid arthritis (RA).Methods: Expression of IL‐7Rα and IL‐7 was determined in synovial tissue from RA patients and was compared with that in synovial tissue from patients with undifferentiated arthritis (UA) and osteoarthritis (OA). IL‐7Rα expression on CD4 T cells, CD19 B cells, and CD14 monocyte/macrophages from RA synovial tissue, synovial fluid, and peripheral blood was also assessed. The proliferative capacity of IL‐7Rα^bright and IL‐7Rα^dim/− T cells was measured. In addition, we examined IL‐7R blockade with soluble human IL‐7Rα (hIL‐7Rα) in the prevention of immune activation of peripheral blood mononuclear cells.Results: We found significantly higher IL‐7Rα expression in RA and UA synovial tissue than in OA synovial tissue, and the level of IL‐7Rα expression correlated significantly with the levels of CD3 and IL‐7 expression. CD4 T cells from RA synovial fluid and synovial tissue strongly expressed IL‐7Rα. A substantial percentage of B cells and macrophages from RA synovial fluid and synovial tissue also expressed IL‐7Rα, although less prominently than T cells. We found that peripheral blood IL‐7Rα^bright T cells that did not express FoxP3 were highly proliferative as compared with IL‐7Rα^dim/− T cells that did express high levels of FoxP3. Soluble hIL‐7Rα inhibited IL‐7–induced proliferation and interferon‐γ production by mononuclear cells from RA patients.Conclusion: Our data suggest that enhanced expression of IL‐7Rα and IL‐7 in RA patients contributes significantly to the joint inflammation by activating T cells, B cells, and macrophages. The inhibition of IL‐7R–mediated immune activation by soluble hIL‐7Rα further indicates an important role of IL‐7Rα in inflammatory responses in RA, suggesting IL‐7Rα as a therapeutic target for immunotherapy in RA.