Stromal cells and osteoclasts are responsible for exacerbated collagen‐induced arthritis in interferon‐β–deficient mice

Abstract

Objective Clinical trials using interferon‐β (IFNβ) in the treatment of rheumatoid arthritis have shown conflicting results. We undertook this study to understand the mechanisms of IFNβ in arthritis at a physiologic level. Methods Collagen‐induced arthritis (CIA) was induced in IFNβ‐deficient and control mice. The role of IFNβ was investigated in both the priming and effector phases of the disease. The effect of IFNβ deficiency on synovial cells, macrophages, and fibroblasts from preimmunized mice was analyzed by flow cytometry, immunohistochemistry, and enzyme‐linked immunosorbent assay. Differences in osteoclast maturation were determined in situ by histology of arthritic and naive paws and by in vitro maturation studies of naive bone marrow cells. The importance of IFNβ‐producing fibroblasts was determined by transfering fibroblasts into mice at the time of CIA immunization. Results Mice lacking IFNβ had a prolonged disease with a higher incidence compared with control mice. IFNβ deficiency was found to influence the effector phase, but not the priming phase, of arthritis. Compared with control mice, IFNβ‐deficient mice had greater infiltration of CD11b+ cells and greater production of tumor necrosis factor α in vivo, and their macrophages and fibroblasts were both more activated in vitro. Moreover, IFNβ‐deficient mice generated a greater number of osteoclasts in vitro, and mice immunized to induce arthritis, but not naive mice, had a greater number of osteoclasts in vivo compared with control mice. Importantly, IFNβ‐competent fibroblasts were able to ameliorate arthritis in IFNβ‐deficient recipients. Conclusion Our data indicate that IFNβ is involved in regulating the activation state of osteoclasts and stromal cells, including macrophages and fibroblasts, but that it has little effect on T cells.