Purpose: Fibroblast-like synoviocytes (FLS) represent one of the principal effectors of joint damage in rheumatoid arthritis (RA). Recent discovery of the circulating fibrocyte, a potential precursor of FLS, has raised issues regarding the characterization of fibrocytes with respect to their morphology and their biological role. In this study, we evaluated the morphology of fibrocytes in vitro and their ability to produce different extracellular matrix (ECM) components in comparison with two populations of RA FLS: synovial fluid FLS (fd-FLS) and intimal lining FLS (td-FLS). We also studied the expression of ECM regulators and a set of cytokine receptors involved in the pathogenesis of RA. Materials and Methods: Fibrocytes were cultured from peripheral blood of patients with RA. FLS were cultured from synovial fluids and tissues. ECM proteins (collagen I (col I) and fibronectin), Matrix metalloproteinases (MMP) (MMP3, and MMP9), ECM regulators (β catenin, TCF4, and c-fos), and cytokine receptors (CXCR1, CXCR2, CXCR3, IL1RI, IL1RII, and IL6Rα) were analyzed using qRT-PCR and/or western blot. Results: Our results demonstrated that fibronectin and MMP3 levels were higher in FLS compared to fibrocytes. Although MMP9 was expressed in the three cell types, its level was greater in fibrocytes than in td/fd FLS. The three cell types expressed CXCR3, IL1RI, IL1RII, and IL6Rα, while the expression of CXCR1 and CXCR2 was restricted to fibrocytes. Conclusion: Our results demonstrated that fibrocytes express ECM molecules and cytokines receptors. The observed differences between fibrocytes and FLS may be due to their distinct functions or differentiation state during RA.Abbreviations: RA: Rheumatoid ArthritisFLS: fibroblast-like synoviocytestd: tissue derivedfd: fluid derivedSF: Synovial FluidWnt: WinglessMMP: Matrix MetalloproteinaseCIA: murine collagen induced arthritisECM: Extracellular matrixcol I: Collagen ITCF/LEF: T-cell factor/lymphoid enhancer-binding factorAP1: Activator Protein 1.

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