Th133 - Single-cell Multi-parametric Analysis of the Enthesitis-related Arthritis (ERA) Synovial and Circulatory Immunomes Evidences a Pathological Chemokine Gradient That Directs CD4+ T Cell-mediated Synovial Inflammation

Jing Yao Leong – Translational Immunology Institute – SingHealth; Amanda Jin Mei Lim – Translational Immunology Institute – SingHealth; Martin Wasser – Translational Immunology Institute – SingHealth; Joo Guan Yeo – Translational Immunology Institute – SingHealth; Thaschawee Arkachaisri – Rheumatology and Immunology Service – KK Women's and Children's Hospital; Salvatore Albani – Translational Immunology Institute – SingHealth

Abstract Text: ERA, a common subtype of JIA, has a poor prognosis. ERA immunopathogenesis remains unclear, especially the ontogeny of synovial pro-inflammatory T cells. We compared, using a high-dimensional approach, the synovial and circulatory immunomes of active ERA patients. We also characterized CD4+ T cell subsets strongly associated with synovial inflammation.

We interrogated, using mass cytometry, synovial (n=10) and peripheral (n=30) CD45+ immune cells from ERA patients with active joint inflammation, as well as cells from blood of healthy pediatric controls (n=30). To evaluate CXCR3+CCR6+CD4+ T cells, we sorted them from active ERA SFMCs and PBMCs and conducted in-vitro maturation and Treg suppression assays.

Inflammation is localized to the synovium, marked by a deranged immune architecture suggestive of DC-mediated CD4+ T cell priming with diminished NK and B cell involvement. Functional derangements in the CD4+ T cell landscape are dominated by Th1 and Th17 cells. The synovium has been shown to be enriched with CXCR3 and CCR6 ligands, and high-dimensional analysis identified a pro-trafficking CXCR3+CCR6+ CD4+ T cell population that migrates into the synovium where they mature into producers of Th1 and Th17 cytokines. The synovial CD4+ Treg landscape displays a suppressive phenotype and is shaped by the same chemokine gradient. CXCR3+CCR6+CD4+ Tregs are bona fide Tregs that are expanded in the synovium and suppress their Teff counterparts, but Teffs may be resistant to suppression in-vivo.

The results suggest a pathogenic chemokine gradient that directs the localization of disease in ERA, whereby Teff activation in the synovium overcomes regulation and perpetuates inflammation.