CD200 and rheumatoid arthritis: Aberrant CD200/CD200R1 expression in RA was shown to contribute to abnormal Th17 cell differentiation, chemotaxis, and osteoclastogenesis; this abnormal expression was corrected after treatment with a TNF-α antagonist plus methotrexate, demonstrating that CD200/CD200R1 exerts anti-inflammatory functions via multiple mechanisms and delineating a potential immunotherapeutic role for targeting CD200/CD200R1 signaling in RA [35].