Abstract
BackgroundPower Doppler ultrasound (PDUS) is increasingly used to assess synovitis in Rheumatoid Arthritis (RA). Prior studies have shown correlations between PDUS scores and vessel counts, but relationships with T cell immunopathology have not been described.Methodology/Principal FindingsPBMC were isolated from healthy controls (HC) or RA patients and stimulated ex vivo with PMA and ionomycin for 3 hours in the presence of Golgistop. Paired synovial fluid (SF) or synovial tissue (ST) were analysed where available. Intracellular expression of IL-17, IFNγ, and TNFα by CD4+ T cells was determined by flow cytometry. Synovial blood flow was evaluated by PDUS signal at the knees, wrists and metacarpophalangeal joints of RA patients. Serum, SF and fibroblast culture supernatant levels of vascular endothelial growth factor-A (VEGF-A) were measured by ELISA. The frequency of IL17+IFNγ-CD4+ T cells (Th17 cells) was significantly elevated in peripheral blood (PB) from RA patients vs. HC (median (IQR) 0.5 (0.28–1.59)% vs. 0.32 (0.21–0.54)%, p = 0.005). Th17 cells were further enriched (mean 6.6-fold increase) in RA SF relative to RA PB. Patients with active disease had a higher percentage of IL-17+ T cells in ST than patients in remission, suggesting a possible role for Th17 cells in active synovitis in RA. Indeed, the percentage of Th17 cells, but not Th1, in SF positively correlated with CRP (r = 0.51, p = 0.04) and local PDUS-defined synovitis (r = 0.61, p = 0.002). Furthermore, patients with high levels of IL-17+CD4+ T cells in SF had increased levels of the angiogenic factor VEGF-A in SF. Finally, IL-17, but not IFNγ, increased VEGF-A production by RA synovial fibroblasts in vitro.Conclusions/SignificanceOur data demonstrate a link between the presence of pro-inflammatory Th17 cells in SF and local PDUS scores, and offer a novel immunological explanation for the observation that rapid joint damage progression occurs in patients with persistent positive PDUS signal.
Highlights
The pathogenesis of Rheumatoid Arthritis (RA) is complex and involves multiple cells and inflammatory mediators, including monocytes/macrophages, fibroblasts, B cells and T cells [1]
Ex vivo (PMA/ionomycin/GolgiStop stimulated for 3 hours) Th17 cell frequencies were significantly elevated in RA patients vs. healthy donors (HC median 0.32, inter-quartile range (IQR) 0.21– 0.54%, RA median 0.5, IQR 0.32–1.68%, p = 0.005), with a suggestion of a bimodal distribution (Fig. 1A) in patients
There were no significant differences in the frequency of Th1 or TNFa-expressing CD4+ T cells between RA patients and healthy controls, these cells were present at higher frequencies than Th17 cells
Summary
The pathogenesis of Rheumatoid Arthritis (RA) is complex and involves multiple cells and inflammatory mediators, including monocytes/macrophages, fibroblasts, B cells and T cells [1]. A large body of literature, in both animal models of experimental arthritis and human disease, demonstrates the critical contribution of pro-inflammatory CD4+ T helper cell subsets to pathogenesis, with particular roles for their signature cytokines IFNc (produced by Th1 cells), IL-17A (produced by Th17 cells) and TNFa (produced by both Th1 and Th17 cells, as well as monocytes/ macrophages) (reviewed in [2]). Multiple animal models have demonstrated key roles of IL-17A ( called IL-17) and Th17 cells in the immunopathology and joint damage of arthritis (reviewed in [3]). Prior studies have shown correlations between PDUS scores and vessel counts, but relationships with T cell immunopathology have not been described
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