Interleukin-20 is triggered by TLR ligands and associates with disease activity in patients with rheumatoid arthritis

- Elevated synovial fluid IL-20 is associated with RA disease activity.
- IL-20 levels are higher in anti-CCP positive RA patients.
- IL-20 production from PBMCs is induced by TNF-independent TLR pathways.

BackgroundInterleukin (IL)-20 is a pro-inflammatory cytokine that may be implicated in the pathogenesis of rheumatoid arthritis (RA). This study aimed to determine the association between IL-20 and disease activity in patients with RA.MethodsThe levels of serum and synovial fluid IL-20 were measured in patients with RA and OA. The disease activity was assessed based on the Disease Activity Score of 28 joints (DAS28). The expression of IL-20 in synovial tissue samples from patients with RA and OA were determined by immunohistochemistry. Immunofluorescence staining was used to co-localize IL-20 with selected cells. The secretion of IL-20 was analysed in human peripheral blood mononuclear cells (PBMCs) of patients with RA.ResultsSynovial fluid and synovial tissue IL-20 were significantly increased in patients with RA compared with patients with OA. The expression of IL-20 in RA synovial tissue was particularly associated with macrophages and neutrophil granulocytes, but also with synovial fibroblasts and lymphocytes. The IL-20 levels in synovial fluid correlated with DAS28 (r = 0.434; p = 0.015) and were significantly elevated in anti-CCP positive RA compared with anti-CCP negative RA (122.3 ± 104.1 pg/ml and 45.9 ± 35.8 pg/ml; p = 0.008). IL-20 production from PBMCs was induced by Poly I:C and LPS but not with pro-inflammatory cytokines, such as TNF-α or IL-1.ConclusionOur data showed that IL-20 is independently associated with RA disease activity and may be triggered by TLR ligands at local sites of inflammation.