Mesenchymal stem cells derived from synovial fluid effectively alleviate immune imbalance in collagen-induced arthritis rats by regulating anti-inflammatory factor levels

Background: Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by synovial inflammation and joint destruction. Mesenchymal stem cells (MSCs) derived from synovial fluid have shown immunomodulatory potential, but their therapeutic effects in RA models remain incompletely understood. Objectives: This study aimed to isolate and characterize synovial fluid-derived MSCs (SF-MSCs) from RA patients and evaluate their therapeutic efficacy in collagen-induced arthritis (CIA) rats. Methods: SF-MSCs were isolated from RA patient synovial fluid and characterized by flow cytometry. CIA was induced in Wistar rats. CIA rats were treated with either methotrexate (MTX, 0.2 mg/kg) or SF-MSCs (1×106 cells/rat) via tail vein injection on days 21, 24, 27 and 30. Paw swelling, arthritis index scores, X-ray imaging, and histopathology were used to assess arthritis severity. In vitro, SF-MSCs were co-cultured with rat peripheral blood mononuclear cells (PBMCs) at a 1:10 ratio and cytokine levels were measured by enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qPCR). Results: SF-MSCs expressed high levels of cluster of differentiation 44 (CD44, 98.2%), CD105 (96.5%) and CD166 (95.8%), but low levels of CD15, CD34 and CD45 (<2%). SF-MSC treatment significantly reduced paw swelling, arthritis index scores, joint space narrowing and bone erosion compared to CIA controls, with effects comparable to MTX. In co-culture experiments, SF-MSCs significantly suppressed interleukin-6 (IL-6), interleukin-17 (IL-17), interleukin-21 (IL-21) and interleukin-23 (IL-23) production while enhancing transforming growth factor-beta (TGF-β) expression in rat PBMCs. Conclusion: SF-MSCs derived from RA patients exhibit potent immunomodulatory effects, alleviating joint inflammation and destruction in CIA rats. These findings support SF-MSC-based therapy as a promising cell-based approach for RA treatment.