Interleukin-23-Dependent/T Cells Produce Interleukin-17 and Accumulate in the Enthesis, Aortic Valve, and Ciliary Body in Mice

ObjectiveThe spondyloarthritides (SpA) are a group of rheumatic diseases characterized by ossification and inflammation of entheseal tissue, the region where tendon attaches to bone. Interleukin-23 (IL-23) is involved in the pathogenesis of SpA by acting on IL-23 receptor (IL-23R) expressed on enthesis-resident lymphocytes. Upon IL-23 binding, CD3+CD4-CD8- tissue-resident lymphocytes secrete IL-17A and IL-22, leading to inflammation, bone loss, and ossification. Knowledge about enthesis-resident lymphocytes remains fragmentary, and the contribution of entheseal / T cells in particular is not clear. This study was undertaken to investigate the presence of / T cells in the enthesis. MethodsWe used 2-photon microscopy and flow cytometry to analyze entheseal lymphocytes from C57BL/6, Tcrd-H2BeGFP, Rorc-GFP, and IL-23R-eGFP mice. To analyze entheseal / T cells in IL-23-induced inflammation, Tcrd-H2BeGFP mice were crossed with mice of the susceptible B10.RIII background. Hydrodynamic injection of IL-23 minicircle DNA was performed for overexpression of IL-23 and induction of inflammation. Light-sheet fluorescence microscopy was used to visualize arthritic inflammation. ResultsActivated V6+CD27- / T cells were abundant in uninflamed entheseal tissue and constituted the large majority of retinoic acid receptor-related orphan nuclear receptor t (RORt)+IL-23R+ enthesis-resident lymphocytes. Fetal thymus-dependent / T cells were the main source of IL-17A at the enthesis. Under inflammatory conditions, / T cells increased in number at the Achilles tendon enthesis, aortic root, and adjacent to the ciliary body. ConclusionEntheseal / T cells are derived from fetal thymus and are maintained as self-renewing tissue-resident cells. As main IL-17A producers within tissues exposed to mechanical stress including enthesis, / T cells are key players in the pathogenesis of IL-23-induced local inflammation.