The systemic JIA synovial fluid environment supports development and prevalence of specific inflammatory T helper cell phenotypes

Objective The potential involvement of adaptive immunity in systemic juvenile idiopathic arthritis (sJIA) pathophysiology remains an intriguing question. Here, we investigated whether and how the inflammatory environment in sJIA versus JIA synovial fluid (SF) may differentially impact T helper (Th) cell polarization and activation. Methods SF samples from sJIA and JIA patients (both n=7) were tested in various cell culture setups, with or without recombinant cytokines or cytokine-blocking drugs, to assess their effects on healthy donor Th cell activation. We analyzed cellular surface marker, transcription factor, and effector molecule expression using flow cytometry, Luminex, ELISA, and qRT-PCR. Results Both sJIA and JIA SF revealed highly pro-inflammatory profiles. Compared to JIA, sJIA SF demonstrated markedly elevated IL-1β, IL-18, GM-CSF, S100A9, and MPO levels, while JIA SF showed trends toward higher soluble FasL and IL-17A concentrations. Notably, sJIA SF significantly increased CD4 T cell ICOS expression and expanded CXCR3 pos CCR6 pos Th cells, whereas JIA SF favored expansion of CXCR3 neg CCR6 pos Th cells and CCR6 pos Th cell expansion was sensitive to IL-1 blockade. Systemic JIA SF selectively sustained a IFNγ/IL-21 expressing T peripheral helper (Tph) phenotype, particularly associated with IL-1β, IL-18, and GM-CSF SF levels. Spiking JIA SF with a cocktail of these cytokines recapitulated some T cellular phenotypic features observed in sJIA SF cultures. Conclusion JIA and sJIA SF drive distinct Th cell polarization, including differential and sustained Tf/ph cell activation. These findings complement our earlier observations in sJIA peripheral blood and demonstrate the impact of the SF inflammatory matrix on immune cell activation. What is already known on this topic Systemic juvenile idiopathic arthritis (sJIA, Still’s Disease) is initially hallmarked by innate immunity driving systemic inflammation With further disease course sJIA can progress to chronic destructive arthritis with several studies suggesting an involvement of adaptive immunity in this process. In a previous study we linked T follicular/peripheral helper (Tfh/Tph) cells in sJIA patients’ blood to arthritis and self-reactive antibody signatures in patients with longer disease duration What this study adds Our study demonstrates that sJIA versus JIA synovial fluid (SF) can drive differential T helper cell (Th cell) polarization and activation. Our data imply that sJIA SF promotes the self-sustenance of Th cells with a Tph phenotype characterized by IFNγ, IL-21 and c-MAF expression. IL-1β, IL-18, and GM-CSF levels in sJIA SF can be associated with Tph perseverance, and recapitulate sJIA Tph features when spiked into JIA SF. How this study might affect research, practice or policy The present data complement our earlier observations from sJIA peripheral blood and strengthen the biphasic model hypothesis regarding sJIA progression While both JIA and sJIA patients can develop clinically similar arthritis, our data demonstrate how the respective local inflammatory environments can differentially impact and shape T cell immunity. Our data suggest a combined and early targeting of both IL-1β and IL-18 in sJIA may be effective in preventing the generation of inflammatory T cell subsets with the potential to drive chronic arthritis through a joint-localized, adaptive immune response.