Gut Inflammation in Axial Spondyloarthritis Patients is Characterized by a Marked Type 17 Skewed Mucosal Innate-like T Cell Signature.

OBJECTIVE: Patients with spondyloarthritis (SpA) often present with microscopic signs of gut inflammation, a risk factor for progressive disease. We investigated whether mucosal innate-like T cells are involved in dysregulated interleukin-23 (IL-23)/IL-17 responses in the gut-joint axis in SpA. METHODS: Ileal and colonic intraepithelial lymphocytes (IELs), lamina propria lymphocytes (LPLs), and paired peripheral blood mononuclear cells (PBMCs) were isolated from treatment-naive patients with nonradiographic axial SpA with (n = 11) and without (n = 14) microscopic gut inflammation and healthy controls (n = 15) undergoing ileocolonoscopy. The presence of gut inflammation was assessed histopathologically. Immunophenotyping of innate-like T cells and conventional T cells was performed using intracellular flow cytometry. Unsupervised clustering analysis was done by FlowSOM technology. Serum IL-17A levels were measured via Luminex. RESULTS: Microscopic gut inflammation in nonradiographic axial SpA was characterized by increased ileal intraepithelial γδ-hi T cells, a γδ-T cell subset with elevated γδ-T cell receptor expression. γδ-hi T cells were also increased in PBMCs of patients with nonradiographic axial SpA versus healthy controls and were strongly associated with Ankylosing Spondylitis Disease Activity Score. The abundance of mucosal-associated invariant T cells and invariant natural killer T cells was unaltered. Innate-like T cells in the inflamed gut showed increased RORγt, IL-17A, and IL-22 levels with loss of T-bet, a signature that was less pronounced in conventional T cells. Presence of gut inflammation was associated with higher serum IL-17A levels. In patients treated with tumor necrosis factor blockade, the proportion of γδ-hi cells and RORγt expression in blood was completely restored. CONCLUSION: Intestinal innate-like T cells display marked type 17 skewing in the inflamed gut mucosa of patients with nonradiographic axial SpA. γδ-hi T cells are linked to intestinal inflammation and disease activity in SpA.

Distinct immune modulatory roles of regulatory T cells in gut versus joint inflammation in TNF-driven spondyloarthritis.

OBJECTIVES: Gut and joint inflammation commonly co-occur in spondyloarthritis (SpA) which strongly restricts therapeutic modalities. The immunobiology underlying differences between gut and joint immune regulation, however, is poorly understood. We therefore assessed the immunoregulatory role of CD4+FOXP3+ regulatory T (Treg) cells in a model of Crohn's-like ileitis and concomitant arthritis. METHODS: RNA-sequencing and flow cytometry was performed on inflamed gut and joint samples and tissue-derived Tregs from tumour necrosis factor (TNF)∆ARE mice. In situ hybridisation of TNF and its receptors (TNFR) was applied to human SpA gut biopsies. Soluble TNFR (sTNFR) levels were measured in serum of mice and patients with SpA and controls. Treg function was explored by in vitro cocultures and in vivo by conditional Treg depletion. RESULTS: Chronic TNF exposure induced several TNF superfamily (TNFSF) members (4-1BBL, TWEAK and TRAIL) in synovium and ileum in a site-specific manner. Elevated TNFR2 messenger RNA levels were noted in TNF∆ARE/+ mice leading to increased sTNFR2 release. Likewise, sTNFR2 levels were higher in patients with SpA with gut inflammation and distinct from inflammatory and healthy controls. Tregs accumulated at both gut and joints of TNF∆ARE mice, yet their TNFR2 expression and suppressive function was significantly lower in synovium versus ileum. In line herewith, synovial and intestinal Tregs displayed a distinct transcriptional profile with tissue-restricted TNFSF receptor and p38MAPK gene expression. CONCLUSIONS: These data point to profound differences in immune-regulation between Crohn's ileitis and peripheral arthritis. Whereas Tregs control ileitis they fail to dampen joint inflammation. Synovial resident Tregs are particularly maladapted to chronic TNF exposure.

RORγt inhibition ameliorates IL-23 driven experimental psoriatic arthritis by predominantly modulating γδ-T cells.

OBJECTIVE: Divergent therapeutic outcomes on different disease domains have been noted with IL-23 and IL-17A-blockade in PsA. Therefore, elucidating the role of RORγt, the master regulator of type 17 immune responses, is of potential therapeutic interest. To this end, RORγt inhibition was assessed in combined skin, joint and gut inflammation in vivo, using a PsA model. METHODS: We tested the efficacy of a RORγt antagonist in B10.RIII mice challenged with systemic overexpression of IL-23 by hydrodynamic injection of IL-23 enhanced episomal vector (IL-23 EEV). Clinical outcomes were evaluated by histopathology. Bone density and surface erosions were examined using micro-computed tomography. Cytokine production was measured in serum and by intracellular flow cytometry. Gene expression in PsA-related tissues was analysed by qPCR. RESULTS: RORγt-blockade significantly ameliorated psoriasis, peripheral arthritis and colitis development in IL-23 EEV mice (improvement of clinical scores and weight loss respectively by 91.8%, 58.2% and 7.0%, P < 0.001), in line with profound suppression of an enhanced type IL-17 immune signature in PsA-affected tissues. Moreover, inflammation-induced bone loss and bone erosions were reduced (P < 0.05 in calcaneus, P < 0.01 in tibia). Sustained IL-23 overexpression resulted in only mild signs of sacroiliitis. Gamma-delta (γδ)-T cells, the dominant source of T cell-derived IL-17A and IL-22, were expanded during IL-23 overexpression, and together with Th17 cells, clearly countered by RORγt inhibition (P < 0.001). CONCLUSION: RORγt-blockade shows therapeutic efficacy in a preclinical PsA model with protection towards extra-musculoskeletal manifestations, reflected by a clear attenuation of type 17 cytokine responses by γδ-T cells and Th17 cells.

RORγt inhibition selectively targets IL-17 producing iNKT and γδ-T cells enriched in Spondyloarthritis patients.

Dysregulated IL-23/IL-17 responses have been linked to psoriatic arthritis and other forms of spondyloarthritides (SpA). RORγt, the key Thelper17 (Th17) cell transcriptional regulator, is also expressed by subsets of innate-like T cells, including invariant natural killer T (iNKT) and γδ-T cells, but their contribution to SpA is still unclear. Here we describe the presence of particular RORγt+T-betloPLZF- iNKT and γδ-hi T cell subsets in healthy peripheral blood. RORγt+ iNKT and γδ-hi T cells show IL-23 mediated Th17-like immune responses and were clearly enriched within inflamed joints of SpA patients where they act as major IL-17 secretors. SpA derived iNKT and γδ-T cells showed unique and Th17-skewed phenotype and gene expression profiles. Strikingly, RORγt inhibition blocked γδ17 and iNKT17 cell function while selectively sparing IL-22+ subsets. Overall, our findings highlight a unique diversity of human RORγt+ T cells and underscore the potential of RORγt antagonism to modulate aberrant type 17 responses.

It Takes "Guts" to Cause Joint Inflammation: Role of Innate-Like T Cells.

Innate-like T cells such as invariant natural killer T (iNKT) cells and mucosal-associated T (MAIT) cells, characterized by a semi-invariant T cell receptor and restriction toward MHC-like molecules (CD1 and MR1 respectively), are a unique unconventional immune subset acting at the interface of innate and adaptive immunity. Highly represented at barrier sites and capable of rapidly producing substantial amounts of cytokines, they serve a pivotal role as first-line responders against microbial infections. In contrast, it was demonstrated that innate-like T cells can be skewed toward a predominant pro-inflammatory state and are consequently involved in a number of autoimmune and inflammatory diseases like inflammatory bowel diseases and rheumatic disorders, such as spondyloarthritis (SpA) and rheumatoid arthritis. Interestingly, there is link between gut and joint disease as they often co-incide and share certain aspects of the pathogenesis such as established genetic risk factors, a critical role for pro-inflammatory cytokines, such as TNF-α, IL-23, and IL-17 and therapeutic susceptibility. In this regard dysregulated IL-23/IL-17 responses appear to be crucial in both debilitating pathologies and innate-like T cells likely act as key player. In this review, we will explore the remarkable features of iNKT cells and MAIT cells, and discuss their contribution to immunity and combined gut-joint disease.

The Role of the Microbiome in Gut and Joint Inflammation in Psoriatic Arthritis and Spondyloarthritis.

Spondyloarthritis (SpA) encompasses a group of diseases characterized by an inflammatory arthritis involving both joints and entheses. However, extraarticular symptoms constitute a large element of the pathology and should not be underestimated. Microscopic gut inflammation is observed in 50% of patients with SpA and has been linked to disease activity, underscoring the effect of gut inflammation in SpA. In this review, we discuss the influence of gut microbiota on SpA pathogenesis. A change in microbiota composition has been linked to the development of various inflammatory arthritides, and dysbiosis is a potential factor in the pathogenesis of multiple inflammatory diseases. In this context, several groups have reported the modulatory effects of gut microbiota-derived metabolites on the effect of immune cells. The gut mucosa is populated by several types of regulatory T cells, but also some specialized unconventional innate-like T cells. These cells are predominantly found at mucosal and epithelial barrier sites, where they serve an essential role in modulating host-microbial interplay. Apart from the close association between the composition of the microbiota and inflammatory diseases, the therapeutic value of dysbiosis needs further investigation, and the identification of a causal inflammatory pathway between gut dysbiosis and musculoskeletal inflammation could revolutionize the therapeutic approach in SpA.