IFNL1 and rheumatoid arthritis: IL‐29 was expressed in CD68+ macrophage and FGF‐2+ fibroblast in the lining layers of RA synovium.31 Expression of IL‐29 was significantly higher in serum, peripheral blood mononuclear cells (PBMCs) and synovial tissue in RA patients compared with that in healthy controls.11, 32 Levels of IL‐29 in synovial fluid (SF) were higher in RA patients compared with that in OA patients.31 Serum levels of IL‐29 positively correlated with rheumatoid factor (RF), anti‐cyclic citrullinated peptide (anti‐CCP) antibody and disease activity score of 28.