Background/Purpose: In rheumatoid arthritis (RA), fibroblast-like synoviocytes (FLS) secrete inflammatory cytokines and chemokines, invade and degrade cartilage, and stimulate osteoclast that cause bone erosion. Recently, it is reported that the subsets of RA FLS in fresh human synovial tissues were characterized by the expression of podoplanin (PDPN), CD34, and THY1 (also known as CD90). Especially PDPN⁺CD34^–THY1⁺ FLS may be pathogenic since these cells secrete proinflammatory cytokines and are proliferative and invasive. Adherent cells with FLS appearance are observed when the cells in synovial fluid (SF) are cultured. The aim of this study is to investigate the subsets of SF-derived FLS in RA.

Methods: We collected the SFs aspirated from the knee joint of RA patients, who were not treated with DMARDs at the onset or at the flare. The SFs were centrifuged and the cell pellets were resuspended in RPMI-1640 medium supplemented with 10% FBS and 1% Pen-Strep. The attached cells were cultured until 80% confluent growth was observed, and these cells were harvested and passaged. The profile of cell surface markers expressed by SF-derived adherent cells were analyzed using flow cytometry. Flow cytometry was performed by triple staining with PDPN, CD34 and THY1. The data are reported as the mean ± SE.

Results: We got the synovial fluid from 17 patients with RA. The characteristics of the 8 patients, whose SF-derived adherent cells were able to be passaged, were long duration of arthralgia (102.1 ± 35.1 vs 11.0 ± 6.9 months, p< 0.05), lower levels of serum rheumatoid factor (30.9 ± 15.5 vs 152.0 ± 48.9 IU/mL, p< 0.05) and lower proportion of lymphocytes of white blood cells in SF ( 11.4 ± 3.2 vs 39.0 ± 10.6 %, p< 0.05). At the passage 0 (n=8), PDPN⁺ cells were lower than PDPN^– cells (35.6 ± 4.1 % and 64.4 ± 4.1 %, respectively, p< 0.05). The proportion of CD34^–THY1⁺, CD34^–THY1^–, CD34⁺THY1⁺, and CD34⁺THY1^– in the PDPN⁺ cells were 54.2 ± 10.8 %, 25.7 ± 12.2 %, 23.1 ± 9.2 %, and 2.2 ± 0.3 % respectively. Among the 3 patients whose cells were passaged up to P2, the rate of PDPN⁺ cells were increased with every repeated the passage (P0: 28.8 ± 4.4 %, P1: 60.3 ± 7.7 %, P2: 71.4 ± 3.2 %). In addition, the rate of CD34⁺THY1⁺ cells in the PDPN⁺ cells were increased (P0: 4.4 ± 1.7 %, P1: 16.9 ± 6.8 %, P2: 25.4 ± 6.0 %).

Conclusion:

These data show that PDPN⁺ SF-derived FLS have the subsets, and CD34^–THY1⁺ cells would be major subsets. PDPN⁺ SF-derived FLS, particularly CD34⁺THY1⁺ cells, are proliferative. Considering SF-derived FLS have the merit of easy accessibility, these cells could substitute for ST-derived FLS in studying the pathogenesis of RA.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/subsets-of-synovial-fluid-derived-fibroblast-like-synoviocytes-in-rheumatoid-arthritis/