Evidence that tissue resident human enthesis γδT-cells can produce IL-17A independently of IL-23R transcript expression

Abstract

ObjectivesMurine models of interleukin (IL)-23-driven spondyloarthritis (SpA) have demonstrated entheseal accumulation of γδT-cells which were responsible for the majority of local IL-17A production. However, IL-23 blockers are ineffective in axial inflammation in man. This study investigated γδT-cell subsets in the normal human enthesis to explore the biology of the IL-23/17 axis.MethodsHuman spinous processes entheseal soft tissue (EST) and peri-entheseal bone (PEB) were harvested during elective orthopaedic procedures. Entheseal γδT-cells were evaluated using immunohistochemistry and isolated and characterised using flow cytometry. RNA was isolated from γδT-cell subsets and analysed by qPCR. Entheseal γδT-cells were stimulated with phorbol 12-myristate 13-acetate (PMA) and ionomycin, anti-CD3/28 or IL-23 and IL-17A production was measured by high-sensitivity ELISA and qPCR.ResultsEntheseal γδT-cells were confirmed immunohistochemically with Vδ1 and Vδ2 subsets that are cytometrically defined. Transcript profiles of both cell populations suggested tissue residency and immunomodulatory status. Entheseal Vδ2 cells expressed high relative abundance of IL-23/17-associated transcripts including IL-23R, RORC and CCR6, whereas the Vδ1 subset almost completely lacked detectable IL-23R transcript. Following PMA stimulation IL-17A was detectable in both Vδ1 and Vδ2 subsets, and following CD3/CD28 stimulation both subsets showed IL-17A and IL-17F transcripts with neither transcript being detectable in the Vδ1 subset following IL-23 stimulation.ConclusionSpinal entheseal Vδ1 and Vδ2 subsets are tissue resident cells with inducible IL-17A production with evidence that the Vδ1 subset does so independently of IL-23R expression.

Interleukin‐23 pathway at the enthesis: The emerging story of enthesitis in spondyloarthropathy

“…The immunopathological importance of IL‐17F is still being deciphered; however, it appears to have overlapping functions with IL‐17A and is also produced by the same T cells . Thus far, there are limited data, showing that IL‐23 stimulation of enthesis‐derived lymphocytes can drive both IL‐17A and IL‐17F transcript expression . It remains to be determined whether a pure IL‐23 blocker or dual antagonism of IL‐17A an IL‐17F will offer advantages in PsA‐related entheseal pathology.…”

“…The highly surprising observation that IL‐23 blockers do not appear to be effective for spinal enthesitis but show efficacy for peripheral enthesitis has been an unexpected finding . It has been established that the spinal enthesis has a resident population of gamma delta T‐cells that can make IL‐17A independently of IL‐23 signaling . However, no data are thus far available on the peripheral skeleton.…”

“…92 Thus far, there are limited data, showing that IL-23 stimulation of enthesis-derived lymphocytes can drive both IL-17A and IL-17F transcript expression. 93 It remains to be determined whether a pure IL-23 blocker or dual antagonism of IL-17A an IL-17F will offer advantages in PsA-related entheseal pathology.…”

“…116,117 It has been established that the spinal enthesis has a resident population of gamma delta T-cells that can make IL-17A independently of IL-23 signaling. 93 However, no data are thus far available on the peripheral skeleton. With the emergent data from genetics and imaging and therapy, the immunological focus of IL-23 pathway research in the skeleton is now firmly pointed at the enthesis.…”

Osteoimmunology in rheumatoid and psoriatic arthritis: potential effects of tofacitinib on bone involvement

“…In particular, the γδ T cells, a minor subset of T cells, have been shown to secrete IL-17, and are of importance in mucosal and epithelial tissue, where their role is to help to bridge innate and adaptive immunity. The majority of the production of IL-17 by γδ T cells follows stimulation by IL-23, but also occurs via IL-23-independent pathways [62]. Recently, IL-17A produced by γδ T cells was shown to increase the proliferation and osteoblastic differentiation of mesenchymal progenitor cells and to promote bone formation in IL-17A−/− mice [63].…”