IL-29 enhances Toll-like receptor-mediated IL-6 and IL-8 production by the synovial fibroblasts from rheumatoid arthritis patients

Introduction: We previously reported that IL-29, a newly described member of interferon (IFN) family, was overexpressed in blood and synovium of rheumatoid arthritis (RA) patients and triggered proinflammatory cytokine IL-6 and IL-8 mRNA expression in RA synovial fibroblasts (RA-FLS). This suggests that IL-29 has an important role in synovial inflammation. Toll-like receptors (TLRs) also activate RA-FLS to produce inflammatory mediators including tumor necrosis factor a (TNF-alpha) and IL-1 beta in RA-FLS. Since the TLR family plays an early role in the innate immune response and the subsequent induction of the adaptive immune response, we hypothesize that IL-29 interacts with TLRs in RA inflammation. This study aimed to investigate the effect of IL-29 on TLR-mediated proinflammatory cytokine production in RA-FLS. Methods: The mRNA level of IL-29 receptors (IL-28R alpha and IL-10R2) in RA-FLS was determined by semi-quantitative RT-PCR. IL-6 and IL-8 mRNA expressions in RA-FLS were evaluated by real-time PCR after pre-incubation with IL-29 and subsequent stimulation with peptidoglycan (PGN, TLR2 ligand), or polycytidylic acid (poly(I: C), TLR3 ligand), or lipopolysaccharide (LPS, TLR4 ligand). The production of TLR2, 3, and 4 in RA-FLS after IL-29 stimulation was also assessed by real-time PCR and flow cytometry. IL-29 mRNA and protein expression in RA-FLS after stimulation with PGN, poly(I: C), or LPS were measured by real-time PCR and enzyme-linked immunosorbent assay (ELISA), respectively. Results: The IL-29 receptor complex (IL-28Ra and IL-10R2) was identified in RA-FLS. IL-29 enhanced TLR-mediated IL-6 and IL-8 expression in RA-FLS. IL-29 upregulated expression of TLR2, 3 and 4 in RA-FLS. Exposure to PGN, poly(I: C) or LPS triggered IL-29 production by RA-FLS. Conclusions: We show for the first time that IL-29 enhances TLR-induced proinflammatory cytokine production in RA-FLS via upregulation of TLRs.