IL-29 Enhances LPS/TLR4-Mediated Inflammation in Rheumatoid Arthritis

Interleukin-29 (IL-29), a critical member of type III interferons (IFNs) family, has been implicated in protecting against viral infection and modulating autoimmune inflammation. Toll-like receptor 4 (TLR4) plays a crucial role in synovial inflammation and may contribute to the pathogenesis of rheumatology arthritis (RA). However, little is known about the modifying effect of IL-29 on TLR4-mediated inflammation in RA. We aim to investigate the potential association between IL-29 and TLR4 in RA.

Peripheral blood mononuclear cells (PBMCs) and serum from 77 patients with RA and 70 controls were collected to determine levels of IL-29 and TLR4 mRNA by real-time polymerase chain reaction (PCR). Levels of IL-29 and TLR4 in synovial tissues and fluid from 25 RA patients and 24 controls were detected by enzyme-linked immunosorbent assay (ELISA) or western blot assay, respectively. RAW264.7 cells were stimulated by lipopolysaccharide (LPS) and/or IL-29. The production of inflammatory cytokines including IL-6, IL-8 as well as TNF-α and the activation of nuclear factor-κB (NF-κB) signaling were determined.

In comparison with controls, increased IL-29 was observed in PBMCs, synovial tissue, serum and synovial fluid of patients with RA. Besides, TLR4 was significantly elevated in PBMCs and synovium of RA patients. Moreover, IL-29 was positively associated with TLR4 in RA, suggested by Pearson's correlation analysis. When RAW264.7 cells were stimulated by LPS with or without IL-29 in vitro, IL-29 could enhance LPS-mediated TLR4 expression and the production of IL-6, IL-8 and TNF-α in RAW264.7 cells via the activation of NF-κB signaling.

The present study suggests, for the first time, that IL-29 can aggravate LPS/TLR4-mediated inflammation in RA depending on NF-κB signaling activation.