Intestinal epithelial expression of human TNF is sufficient to induce small bowel inflammation and sacroiliitis mimicking human Spondyloarthritis.

OBJECTIVES: Gut and joint disease commonly co-occur in spondyloarthritis (SpA). Up to 50% of SpA-patients show signs of subclinical gut inflammation and 10% evolves into inflammatory bowel disease (IBD). However, the mechanisms underlying this gut-joint axis are still unclear. Here we tested the hypothesis whether restricted expression of a pro-inflammatory cytokine in the intestine may trigger onset of combined gut and joint inflammation. METHODS: Intestinal expression of human TNF (hTNF) was achieved by driving hTNF gene expression under control of the rat FAPB2 promoter, creating a new animal model, the TNFgut mice, which expresses hTNF in the proximal intestinal tract. Intestinal-specific TNFgut mice were examined for pathological changes in the intestine and extra-intestinal tissues by means of histology, qPCR and flow cytometry, along with 16S sequencing on stools. RESULTS: Local expression of hTNF in the epithelium of the small intestine induces a pro-inflammatory state of the proximal intestinal tract with epithelial alterations and induction of members of the S100 family, as well as local upregulation of T helper 17 and regulatory T cells, but no obvious signs of dysbiosis. Curiously, TNFgut mice develop sacroiliitis (p< 0.05) in addition to small bowel inflammation (p< 0.05). However, no signs of peripheral arthritis nor enthesitis could be documented. CONCLUSION: Intestinal expression of hTNF is sufficient to initiate a pro-inflammatory cascade culminating in small bowel inflammation and sacroiliitis. Thus, gut-derived cytokines are sufficient to induce spondyloarthritis.

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.

ER stress in antigen-presenting cells promotes NKT cell activation through endogenous neutral lipids.

CD1d-restricted invariant natural killer T (iNKT) cells constitute a common glycolipid-reactive innate-like T-cell subset with a broad impact on innate and adaptive immunity. While several microbial glycolipids are known to activate iNKT cells, the cellular mechanisms leading to endogenous CD1d-dependent glycolipid responses remain largely unclear. Here, we show that endoplasmic reticulum (ER) stress in APCs is a potent inducer of CD1d-dependent iNKT cell autoreactivity. This pathway relies on the presence of two transducers of the unfolded protein response: inositol-requiring enzyme-1a (IRE1α) and protein kinase R-like ER kinase (PERK). Surprisingly, the neutral but not the polar lipids generated within APCs undergoing ER stress are capable of activating iNKT cells. These data reveal that ER stress is an important mechanism to elicit endogenous CD1d-restricted iNKT cell responses through induction of distinct classes of neutral lipids.