Pathogenic role of the CXCL16-CXCR6 pathway in rheumatoid arthritis

Objective. Rheumatoid arthritis (RA) is a chronic inflammatory disease associated with massive T cell infiltration into the synovium. The accumulated T cells express type I cytokines, such as interferon-gamma (IFN gamma) and tumor necrosis factor a, and activated markers of inflammation, such as CD154 and inducible costimulator (ICOS). It is thought that chemokines contribute to T cell accumulation in the synovium. In this study, we examined the role of CXCL16 and CXCR6 in T cell migration and stimulation in RA synovium. Methods. Expression of CXCL16 and CXCR6 was analyzed by immunohistochemistry, reverse transcription-polymerase chain reaction, Western blotting, and/or flow cytometry. Migration activity was assessed using a chemotaxis chamber. IFN-gamma production was analyzed by enzyme-linked immunosorbent assay. The effect of anti-CXCL16 monoclonal antibody on murine collagen-induced arthritis (CIA) was evaluated. Results. CXCL16 was expressed in RA synovium. CXCR6 was expressed more frequently on synovial T cells than in peripheral blood. Moreover, CXCR6-positive synovial T cells more frequently expressed CD154 and ICOS than did CXCR6-negative T cells. Stimulation with interleukin-15 (IL-15) up-regulated the expression of CXCR6 on peripheral blood T cells, and then stimulation with CXCL16 induced migration of IL-15-stimulated T cells and enhanced IFN gamma production. Furthermore, anti-CXCL16 monoclonal antibody significantly reduced the clinical arthritis score and reduced infiltration of inflammatory cells and bone destruction in the synovium of mice with CIA. Conclusion. Our results indicate that CXCL16 plays an important role in T cell accumulation and stimulation in RA synovium and suggest that CXCL16 could be a target molecule in new therapies for RA.