Circulating interleukin-39 as a potential biomarker for rheumatoid arthritis diagnosis

•Serum IL-39 levels were significantly higher in patients with RA.•Serum IL-39 levels positively correlated with rheumatoid factor, erythrocyte sedimentation rate, and IgM.•IL-39 may serve as biomarker for the diagnosis of RA. Imbalances in cytokine networks have been shown to be a possible cause of rheumatoid arthritis (RA). The interleukin (IL)-12 family is involved in the pathogenesis of autoimmune diseases including RA, while IL-39 is a newly discovered member of the IL-12 family, although its role in RA remains unclear. The purpose of the present study was to detect the expression of IL-39 in the sera of patients with RA and its relationship with RA activity. We recruited 46 patients with RA and 35 healthy controls at Ningbo Sixth Hospital. Blood samples were collected for biochemical analysis, and disease activity scores of 28 joints based on C-reactive protein were monitored. Serum concentrations of IL-39 were determined using an enzyme-linked immunosorbent assay. The Pearson correlation test was used to analyze the association between serum IL-39 levels and clinical indicators. Serum levels of IL-39 were significantly higher in patients with RA compared with healthy controls (p