The pathogenesis of juvenile idiopathic arthritis (JIA) is thought to involve multiple components of the cellular immune system, including subsets of γδ T cells. In this study, we conducted experiments to define the functional roles of one of the major synovial fluid (SF) T cell subsets, Vγ9+Vδ2+ (Vγ9+) T cells, in JIA. We found that as opposed to CD4+ T cells, equally high percentages (∼35%) of Vγ9+ T cells in SF and peripheral blood (PB) produced TNF-α and IFN-γ. Furthermore, stimulation with isopentenyl pyrophosphate (IPP), a metabolite in the mevalonate pathway, which is a specific potent Ag for Vγ9Jγ1.2+ T cells, similarly amplified cytokine secretion by SF and PB Vγ9+ T cells. Significantly, the SF subset expressed higher levels of CD69 in situ, suggesting their recent activation. Furthermore, 24-h coculturing with SF-derived fibroblasts enhanced CD69 on the SF > PB Vγ9+ T cells, a phenomenon strongly augmented by zoledronate, a farnesyl pyrophosphate synthase inhibitor that increases endogenous intracellular IPP. Importantly, although Vγ9+ T cell proliferation in response to IPP was significantly lower in SF than PBMC cultures, it could be enhanced by depleting SF CD4+CD25+FOXP3+ cells (regulatory T cells). Furthermore, coculture with the Vγ9+ T cells in medium containing zoledronate or IPP strongly increased SF-derived fibroblasts' apoptosis. The findings that IPP-responsive proinflammatory synovial Vγ9+ T cells for which proliferation is partly controlled by regulatory T cells can recognize and become activated by SF fibroblasts and then induce their apoptosis suggest their crucial role in the pathogenesis and control of synovial inflammation.

No abstract

The percentage of Vδ1+ and Vγ9+ γδT cells among the SF T cells and their ability to respond to IPP or IL-2 correlated with specific outcomes of JIA, suggesting their role in the immunopathogenesis of this disease.