IL-18 receptor- signalling pathway contributes to autoantibody-induced arthritis via neutrophil recruitment and mast cell activation

Objectives: The interleukin (IL)-18 signalling pathway is involved in animal models of collagen-induced arthritis, but the role of this pathway in autoantibody-induced arthritis is poorly understood. An autoantibody-induced arthritis model, K/BxN serum transfer arthritis, reflects the effector phase of arthritis and is important in innate immunity including neutrophils and mast cells. This study aimed to investigate the role of the IL-18 signalling pathway in autoantibody-induced arthritis using IL-18 receptor (IL-18R) alpha-deficient mice. Methods: K/BxN serum transfer arthritis was induced in IL-18R alpha(-/-) and wild-type B6 (controls) mice. The severity of arthritis was graded, and histological and immunohistochemical examinations were performed on paraffin-embedded ankle sections. Total Ribonucleic acid (RNA) isolated from mouse ankle joints was analysed by real-time reverse transcriptase-polymerase chain reaction. Results: IL-18 R alpha(-/-) mice had significantly lower arthritis clinical scores, neutrophil infiltration, and numbers of activated, degranulated mast cells in the arthritic synovium than in controls. IL-1 beta, which is indispensable for the progression of arthritis, was significantly downregulated in inflamed ankle tissue in IL-18 R alpha(-/-) mice. Conclusions: IL-18/IL-18R alpha signalling contributes to the development of autoantibody-induced arthritis by enhancing synovial tissue expression of IL-1 beta and inducing neutrophil recruitment and mast cell activation. Therefore, inhibition of the IL-18R alpha signalling pathway might be a new therapeutic strategy for rheumatoid arthritis.