Background/Purpose: Synovial fibroblasts in rheumatoid arthritis (RA) secrete inflammatory cytokines and chemokines, invade and degrade cartilage, and make pannus formation. Synovial fibroblasts characterized by the expression podoplanin (PDPN) are composed three functionally distinct subsets, CD34^–THY1^–, CD34^–THY1⁺, and CD34⁺THY1⁺ population. It is reported that the phenotypical and functional characterization of synovial fluid (SF) derived fibroblast do not deviate from synovial tissue fibroblast. The objective of this study is to investigate phenotypic characterization of SF derived fibroblast and the difference of subsets proportion in clinical features of RA.

Methods: We consecutively collected the SF samples aspirated from knee joint of RA patients at the new-onset or at the flare. The SFs were centrifuged and the cell pellets were resuspended in medium. The attached cells were cultured until 80% confluent growth was observed, and cells were harvested and passaged. Flow cytometry was performed by triple staining with PDPN, CD34 and THY1. The data are expressed as median (25-75 percentile).

Results: We got the SFs from 37 patients with RA. At the primary culture, CD34^–THY1⁺ and CD34^–THY1^– were major subsets [36.1% (9.5-66.0) and 61.6% (24.0-84.6), respectively] in PDPN⁺ fibroblasts [11.2% (5.2-23.2)]. The proportion of CD34^–THY1⁺ subsets in new-onset group (n=25) was higher those in flare group (n=12) [58.7% (16.4-79.2) and 13.8% (8.8-33.5), respectively, p< 0.001]. The proportion of CD34^–THY1^– subsets in flare group was higher those in new-onset group [78.3% (62.8-86.4) and 39.1% (7.8-78.2), respectively, p< 0.001]. Furthermore, the proportion of CD34^–THY1⁺ subsets in seronegative RA (n=18) was higher than those in seropositive RA (n=19) [58.7% (23.0-80.5) and 18.9% (7.5-43.0), respectively, p< 0.05]. By passaging from P0 to P2 (n=22), the proportion of PDPN⁺ fibroblasts was increased. The proportions of CD34⁺THY1⁺ and CD34^–THY1⁺ subsets were also increased, while the proportion of CD34^–THY1^– was decreased. Comparing these differences between the new-onset group (n=13) and the flare group (n=9), the proportion of PDPN⁺ fibroblasts in the new-onset group was increased with a statistically significant difference. In addition, the proportions of CD34⁺THY1⁺ and CD34^–THY1⁺ subsets in the flare group were statistically significantly increased.

Conclusion: These data show that the major subset proportion of SF-derived fibroblasts is different between at the new-onset and at the flare, or seropositive and seronegative. Moreover, the subset of CD34^–THY1⁺ and CD34⁺THY1⁺ have proliferative phenotype. The difference of SF-derived fibroblast subsets proportion may be involved in clinical features in RA.

« Back to ACR Convergence 2022

ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-subsets-of-synovial-fluid-derived-fibroblasts-in-clinical-features-of-rheumatoid-arthritis/