Since the synovial level of SDF-1 was strongly correlated with the disease activity score (DAS28 CRP) and inflammation markers (serum C-reactive protein and IL-6) (109, 110), the decrease of synovial DPP4 in RA may lead to synovial inflammation via SDF-1/CXCR4 axis. The gene discussed is CXCR4; the disease is rheumatoid arthritis.