Background Programmed cell death 5 (PDCD5) is a novel apoptotic regulatory gene that promotes apoptosis in various tumor cells.Studies have shown that PDCD5 accelerates the apoptosis of synoviocytes in vitro,implying a potential role in rheumatoid arthritis (RA) pathogenesis.This study examined the expression of PDCD5 in serum and synovial fluid of RA patients,its effect on the expression of inflammatory cytokine,interleukin-17 (IL-17),and the assessment of disease activity in RA.Methods PDCD5 and IL-17 levels in serum and synovial fluid from 18 patients with RA and 22 patients with osteoarthritis (OA) were detected using enzyme-linked immunosorbent assay (ELISA).Concentrations of serum PDCD5 in 40 healthy people were also detected as controls.As disease activity indices,C-reactive protein (CRP),erythrocyte sedimentation rate (ESR),rheumatoid factor (RF),and X-ray grading scale were also evaluated.Results Serum and synovial fluid PDCD5 levels in RA patients were significantly higher than those in OA and healthy controls.Serum PDCD5 level was inversely correlated to CRP and ESR,and was significantly higher in the RF negative group than in the positive group.PDCD5 level was also negatively correlated with IL-17 levels both in serum and synovial fluid of RA patients.However,differences in synovial fluid PDCD5 level from RA patients at different Larsen stages were not detectable.Conclusions PDCD5 affects RA pathogenesis.Insufficient apoptosis of fibroblast-like synoviocytes and inflammatory cells in RA could increase the expression of PDCD5 protein.As PDCD5 levels correlated negatively with disease activity indices and IL-17 level,PDCD5 could become a target in the diagnosis and treatment of RA.