Reciprocal cross-talk between RANKL and interferon-γ-inducible protein 10 is responsible for bone-erosive experimental arthritis

Objective. Interferon-gamma-inducible protein 10 (IP-10; also called CXCL10), a chemokine important in the migration and proliferation of T cells, is induced in a wide variety of cell types. However, the role of IP-10 in rheumatoid arthritis (RA) remains largely unknown. The purpose of this study was to examine the potential role of IP-10 in bone resorption and RA through examination of a mouse model of collagen-induced arthritis (CIA). Methods. The effects of IP-10 on mouse T cells during osteoclast differentiation were examined in migration assays. The bone-erosive activity of IP-10 was determined in vivo in a mouse model of CIA by histologic and immunostaining analyses. Cytokine levels in serum and culture medium were measured with sandwich enzyme-linked immunosorbent assays. Results. Serum concentrations of IP-10 were significantly higher in mice with CIA than in control mice. RANKL greatly induced IP-10 expression in osteoclast precursors, but not in mature osteoclasts. IP-10 stimulated the expression of RANKL and tumor necrosis factor a (TNF alpha) in CD4+ T cells and induced osteoclastogenesis in cocultures of CD4+ T cells and osteoclast precursors. However, IP-10 did not induce RANKL or TNFa in CD8+ T cells. Treatment with neutralizing antibody to IP-10 significantly inhibited the infiltration of CD4+ T cells and F4/80+ macrophages into the synovium and attenuated bone destruction in mice with CIA. Furthermore, levels of RANKL and TNFa were inhibited by antibody to IP-10. Bone erosion was observed in mice infected with an IP-10 retrovirus. Conclusion. Our findings suggest that IP-10 plays a critical role in the infiltration of CD4+ T cells and F4/80+ macrophages into inflamed joints and causes bone destruction. Our results provide the first evidence that IP-10 contributes to the recruitment of inflammatory cells and is involved in bone erosion in inflamed joints.