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Inflammatory bowel disease (IBD), including Crohn’s disease (CD) and ulcerative colitis (UC), is characterized by chronic, relapsing intestinal inflammation. Galectin-1 (Gal-1) is an endogenous lectin with key pro-resolving roles, including induction of T-cell apoptosis and secretion of immunosuppressive cytokines. Despite considerable progress, the relevance of Gal-1-induced T-cell death in inflamed tissue from human IBD patients has not been ascertained. Intestinal biopsies and surgical specimens from control patients (n = 52) and patients with active or inactive IBD (n = 97) were studied. Gal-1 expression was studied by RT-qPCR, immunoblotting, ELISA and immunohistochemistry. Gal-1-specific ligands and Gal-1-induced apoptosis of lamina propria (LP) T-cells were determined by TUNEL and flow cytometry. We found a transient expression of asialo core 1-O-glycans in LP T-cells from inflamed areas (p

Purpose Proteases play an essential role in the pathophysiology of inflammatory bowel disease (IBD), contributing to the intestinal mucosal lesions through the degradation of the extracellular matrix and alteration of the barrier function. Ulcerative colitis (UC) is characterized by an extensive infiltrate of neutrophils into the mucosa and hence, increased proteolytic activity. Human neutrophil elastase (HNE) is a serine protease that has been reported to be increased in UC patients' intestinal mucosa. Based on our previous studies, we hypothesized that HNE might induce proteolytic degradation and loss of function of therapeutic monoclonal antibodies in IBD patients. Patients and Methods Elastase expression and elastinolytic activity were determined in mucosal explants from ulcerative colitis patients (n=6) and cultured ex vivo in the presence or absence of recombinant elafin. Enzymatic digestions of therapeutic monoclonal antibodies were performed using recombinant HNE and elafin. The integrity of the therapeutic antibodies was evaluated by immunoblotting and protein G binding assay, whereas their TNF-neutralizing activity was assessed with a reporter cell line. Results We found that HNE and its elastinolytic activity were increased in the gut mucosa of UC patients. We also demonstrated that HNE cleaved biological drugs, impairing the TNF-α neutralizing capacity of anti-TNF monoclonal antibodies. This proteolytic degradation was inhibited by the addition of the specific inhibitor, elafin. Conclusion Our results suggest that the high level of proteolytic degradation by mucosal neutrophil elastase, along with a potential imbalance with elafin, contributes to the loss of function of biologic agents, which are currently used in patients with IBD. These findings might explain the non-responsiveness of UC patients to therapeutic monoclonal antibodies and suggest the potential beneficial concomitant use of elafin in this treatment.

Proteolysis-Targeting Chimeras (PROTACs) are heterobifunctional small-molecules that can promote the rapid and selective proteasome-mediated degradation of intracellular proteins through the recruitment of E3 ligase complexes to non-native protein substrates. The catalytic mechanism of action of PROTACs represents an exciting new modality in drug discovery that offers several potential advantages over traditional small-molecule inhibitors, including the potential to deliver pharmacodynamic (PD) efficacy which extends beyond the detectable pharmacokinetic (PK) presence of the PROTAC, driven by the synthesis rate of the protein. Herein we report the identification and development of PROTACs that selectively degrade Receptor-Interacting Serine/Threonine Protein Kinase 2 (RIPK2) and demonstrate in vivo degradation of endogenous RIPK2 in rats at low doses and extended PD that persists in the absence of detectable compound. This disconnect between PK and PD, when coupled with low nanomolar potency, offers the potential for low human doses and infrequent dosing regimens with PROTAC medicines., Mares et al. develop Proteolysis-Targeting Chimeras (PROTACs) that degrade its target RIPK2 in vivo at low doses for a prolonged period of time. This study suggests that PROTAC has a therapeutic potential that is superior to traditional RIPK2 small-molecule inhibitors.

Anti-TNFα and anti-IL-23 antibodies are highly effective therapies for Crohn’s disease or ulcerative colitis in a proportion of patients. V56B2 is a novel bispecific domain antibody in which a llama-derived IL-23p19-specific domain antibody, humanised and engineered for intestinal protease resistance, V900, was combined with a previously-described TNFα-specific domain antibody, V565. V56B2 contains a central protease-labile linker to create a single molecule for oral administration. Incubation of V56B2 with trypsin or human faecal supernatant resulted in a complete separation of the V565 and V900 monomers without loss of neutralising potency. Following oral administration of V900 and V565 in mice, high levels of each domain antibody were detected in the faeces, demonstrating stability in the intestinal milieu. In ex vivo cultures of colonic biopsies from IBD patients, treatment with V565 or V900 inhibited tissue phosphoprotein levels and with a combination of the two, inhibition was even greater. These results support further development of V56B2 as an oral therapy for IBD with improved safety and efficacy in a greater proportion of patients as well as greater convenience for patients compared with traditional monoclonal antibody therapies.

The ST2/IL33 signalling pathway has been associated with ulcerative colitis (UC). ST2, encoded by the IL1RL1 gene, is expressed as both a membrane-anchored receptor (ST2L) activated by IL33 and as a soluble receptor (sST2) with anti-inflammatory properties. In UC patients, sST2 is further increased by corticosteroid treatment; however, the glucocorticoid-mediated molecular regulation remains unknown. We therefore tested whether genetic variants in the IL1RL1 distal promoter are involved in UC and affect glucocorticoid-mediated ST2 expression. Serum ST2 levels and genetic variants in the IL1RL1 distal promoter were examined by ELISA and PCR sequencing in UC patients receiving corticosteroids. Glucocorticoid-mediated ST2 production was evaluated in intestinal mucosa cultures. Molecular regulation of glucocorticoid-mediated ST2 was assessed by RT-qPCR, ChIP assay and luciferase reporter assay. Dexamethasone effect on ST2 transcript expression was analyzed in leukocytes and related to IL1RL1 variants. Sequencing of a distal IL1RL1 promoter region demonstrated that SNPs rs6543115(C) and rs6543116(A) are associated with increased sST2 in UC patients on corticosteroids. Dexamethasone up-regulated sST2 transcription through interaction with the glucocorticoid-response element (GRE) carrying rs6543115(C) variant. Our data indicate that IL1RL1 SNPs rs6543115(C) confer susceptibility to UC and is contained in the GRE, which may modulate glucocorticoid-induced sST2 expression.

The gut barrier plays a crucial role by spatially compartmentalizing bacteria to the lumen through the production of secreted mucus and is fortified by the production of secretory IgA (sIgA) and antimicrobial peptides and proteins. With the exception of sIgA, expression of these protective barrier factors is largely controlled by innate immune recognition of microbial molecular ligands. Several specialized adaptations and checkpoints are operating in the mucosa to scale the immune response according to the threat and prevent overreaction to the trillions of symbionts inhabiting the human intestine. A healthy microbiota plays a key role influencing epithelial barrier functions through the production of short-chain fatty acids (SCFAs) and interactions with innate pattern recognition receptors in the mucosa, driving the steady-state expression of mucus and antimicrobial factors. However, perturbation of gut barrier homeostasis can lead to increased inflammatory signaling, increased epithelial permeability, and dysbiosis of the microbiota, which are recognized to play a role in the pathophysiology of a variety of gastrointestinal disorders. Additionally, gut-brain signaling may be affected by prolonged mucosal immune activation, leading to increased afferent sensory signaling and abdominal symptoms. In turn, neuronal mechanisms can affect the intestinal barrier partly by activation of the hypothalamus-pituitary-adrenal axis and both mast cell-dependent and mast cell-independent mechanisms. The modulation of gut barrier function through nutritional interventions, including strategies to manipulate the microbiota, is considered a relevant target for novel therapeutic and preventive treatments against a range of diseases. Several biomarkers have been used to measure gut permeability and loss of barrier integrity in intestinal diseases, but there remains a need to explore their use in assessing the effect of nutritional factors on gut barrier function. Future studies should aim to establish normal ranges of available biomarkers and their predictive value for gut health in human cohorts.

Type 1 interferon (IFN-1) promotes regulatory T-cell function to suppress inflammation in the mouse intestine, but little is known about IFN-1 in the human gut. We therefore assessed the influence of IFN-1 on CD4+ T-cells isolated from human colon tissue obtained from healthy controls or patients with inflammatory bowel disease (IBD). Immunofluorescent imaging revealed constitutive expression of IFNβ in human intestinal tissue, and colonic T-cells were responsive to exogenous IFN-1 as assessed by phosphorylation of signal transduction and activator of transcription 1 (pSTAT1) and induction of interferon stimulated genes (ISGs). Unlike their blood counterparts, intestinal T-cells from non-inflamed regions of IBD colon displayed enhanced responsiveness to IFN-1, increased frequency of pSTAT1+ cells, and greater induction of ISGs upon IFN-1 exposure in vitro. In healthy tissue, antibody neutralization of IFNβ selectively reduced T-cell production of the pro-regulatory cytokine interleukin-10 (IL-10) and increased IFNγ synthesis. In contrast, neutralization of IFNβ in IBD tissue cultures increased the frequency of T-cells producing inflammatory cytokines but did not alter IL-10 expression. These data support a role for endogenous IFN-1 as a context-dependent modulator of T-cell function that promotes regulatory activity in healthy human intestine, but indicate that the IFN-1/STAT1 pathway is dysregulated in inflammatory bowel disease.

Citrobacter rodentium is a natural non-invasive bacterial pathogen which infects the distal colon of mice. It uses the same molecular mechanisms of type III secretion as human enteropathogenic and enterohemorrhagic Escherichia coli to colonise the epithelial cells of the gut and is therefore an ideal model to study host-bacterial pathogen interactions in vivo. Infection elicits mucosal inflammation with similarities to inflammatory bowel disease, and so it is a readily accessible model to investigate the relationship between inflammation and anti-bacterial immunity in the gut.

Background: Heterozygous germline loss-of-function mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene are usually associated with acromegaly or gigantism due to a young-onset somatotropinoma. AIP functions as a tumor suppressor gene in the pituitary, while its role in other tumours is unknown. AIP is highly expressed in patients with Diffuse Large B Cell Lymphoma (DLBCL) compared to any other tumor type. DLBCL arises from germinal centre B cells which characteristically express the transcriptional repressor B cell lymphoma-6 (BCL6), key for germinal centre formation. Increased expression of BCL6 can lead to the development of DLBCL. Despite the obvious importance of BCL6 expression in GC B cells, the mechanisms by which it is regulated are still poorly understood. Aim: The aim of this study was to investigate the relationship of the high AIP expression, BCL6 and the pathobiology of DLBCL. Methods: We generated mice carrying a conditional homozygous deletion of Aip in T and B cells (Aipfl/fl;Rag1Cre/+). Co-localization of AIP and members of the BCL6 ubiquitination/proteasome pathway by immunofluorescence analysis. Ubiquitin-mediated proteasomal degradation study was done by immuno-precipitation (IP). Results: Our study found that AIP is highly expressed in DLBCL. Genetic deletion of Aip revealed that AIP supported BCL6 expression in mice. The ubiquitin E3 ligase FBXO11 has been previously shown to add ubiquitin to BCL6. We found that AIP could bind to the deubiquitinase UCHL1 and that UCHL1 could remove ubiquitin from BCL6 thereby supporting BCL6 expression by preventing FBXO11 mediated degradation of BCL6 recapitulating what we observed in Aip deficient B cells. Conclusions: The data presented here reveal AIP to be a novel positive regulator of BCL6 protein expression which is commonly up-regulated in DLBCL and prevents FBXO11 degradation of BCL6 by enabling the UCHL1 to remove ubiquitin from BCL6. Therefore, AIP is a potential novel therapeutic target to treat DLBCL. It appears that AIP function as a tumor suppressor in the pituitary and as an oncogene to the pathobiology of DLBCL. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. Abstracts presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.

TNFα is an important cytokine in inflammatory bowel disease. V565 is a novel anti-TNFα domain antibody developed for oral administration in IBD patients, derived from a llama domain antibody and engineered to enhance intestinal protease resistance. V565 activity was evaluated in TNFα-TNFα receptor-binding ELISAs as well as TNFα responsive cellular assays and demonstrated neutralisation of both soluble and membrane TNFα with potencies similar to those of adalimumab. Although sensitive to pepsin, V565 retained activity after lengthy incubations with trypsin, chymotrypsin, and pancreatin, as well as mouse small intestinal and human ileal and faecal supernatants. In orally dosed naïve and DSS colitis mice, high V565 concentrations were observed in intestinal contents and faeces and immunostaining revealed V565 localisation in mouse colon tissue. V565 was detected by ELISA in post-dose serum of colitis mice, but not naïve mice, demonstrating penetration of disrupted epithelium. In an ex vivo human IBD tissue culture model, V565 inhibition of tissue phosphoprotein levels and production of inflammatory cytokine biomarkers was similar to infliximab, demonstrating efficacy when present at the disease site. Taken together, results of these studies provide confidence that oral V565 dosing will be therapeutic in IBD patients where the mucosal epithelial barrier is compromised.

Objective The short isoform of thymic stromal lymphopoietin (TSLP), a cytokine constitutively expressed by epithelial cells, is crucial in preserving immune tolerance in the gut. TSLP deficiency has been implicated in sustaining intestinal damage in Crohn9s disease. We explored mucosal TSLP expression and function in refractory and uncomplicated coeliac disease (CD), a T-cell-mediated enteropathy induced by gluten in genetically susceptible individuals. Design TSLP isoforms—long and short—and receptors—TSLPR and interleukin (IL)-7Rα—were assessed by immunofluorescence, immunoblotting and qRT-PCR in the duodenum of untreated, treated, potential and refractory patients with CD. The ability of the serine protease furin or CD biopsy supernatants to cleave TSLP was evaluated by immunoblotting. The production of interferon (IFN)-γ and IL-8 by untreated CD biopsies cultured ex vivo with TSLP isoforms was also assessed. Results Mucosal TSLP, but not TSLPR and IL-7Rα, was reduced in untreated CD and refractory CD in comparison to treated CD, potential CD and controls. Transcripts of both TSLP isoforms were decreased in active CD mucosa. Furin, which was overexpressed in active CD biopsies, was able to cleave TSLP in vitro. Accordingly, refractory and untreated CD supernatants showed higher TSLP-degrading capacity in comparison to treated CD and control supernatants. In our ex vivo model, both TSLP isoforms significantly downregulated IFN-γ and IL-8 production by untreated CD biopsies. Conclusions Reduced mucosal TSLP expression may contribute to intestinal damage in refractory and untreated CD. Further studies are needed to verify whether restoring TSLP might be therapeutically useful especially in refractory patients with CD.

Intestinal barrier integrity is a prerequisite for homeostasis of mucosal function, which is balanced to maximise absorptive capacity, while maintaining efficient defensive reactions against chemical and microbial challenges. Evidence is mounting that disruption of epithelial barrier integrity is one of the major aetiological factors associated with several gastrointestinal diseases, including infection by pathogens, obesity and diabetes, necrotising enterocolitis, irritable bowel syndrome and inflammatory bowel disease. The notion that specific probiotic bacterial strains can affect barrier integrity fuelled research in whichin vitrocell lines, animal models and clinical trials are used to assess whether probiotics can revert the diseased state back to homeostasis and health. This review catalogues and categorises the lines of evidence available in literature for the role of probiotics in epithelial integrity and, consequently, their beneficial effect for the reduction of gastrointestinal disease symptoms.

Colorectal cancers (CRCs) often show a dense infiltrate of cytokine-producing immune/inflammatory cells. The exact contribution of each immune cell subset and cytokine in the activation of the intracellular pathways sustaining CRC cell growth is not understood. Herein, we isolate tumor-infiltrating leukocytes (TILs) and lamina propria mononuclear cells (LPMCs) from the tumor area and the macroscopically unaffected, adjacent, colonic mucosa of patients who underwent resection for sporadic CRC and show that the culture supernatants of TILs, but not of LPMCs, potently enhance the growth of human CRC cell lines through the activation of the oncogenic transcription factors signal transducer and activator of transcription 3 (STAT3) and nuclear factor-kappa B (NF-kB). Characterization of immune cell complexity of TILs and LPMCs reveals no differences in the percentages of T cells, natural killer T cells, natural killer (NK) cells, macrophages and B cells. However, T cells from TILs show a functional switch compared with those from LPMCs to produce large amounts of T helper type 17 (Th17)-related cytokines (that is, interleukin-17A (IL-17A), IL-17F, IL-21 and IL-22), tumor necrosis factor-alpha (TNF-alpha) and IL-6. Individual neutralization of IL-17A, IL-17F, IL-21, IL-22, TNF-alpha or IL-6 does not change TIL-derived supernatant-driven STAT3 and NF-kB activation, as well as their proproliferative effect in CRC cells. In contrast, simultaneous neutralization of both IL-17A and TNF-alpha, which abrogates NF-kB signaling, and IL-22 and IL-6, which abrogates STAT3 signaling, reduces the mitogenic effect of supernatants in CRC cells. IL-17A, IL-21, IL-22, TNF-alpha and IL-6 are also produced in excess in the early colonic lesions in a mouse model of sporadic CRC, associated with enhanced STAT3/NF-kB activation. Mice therapeutically given BP-1-102, an orally bioavailable compound targeting STAT3/NF-kB activation and cross-talk, exhibit reduced colon tumorigenesis and diminished expression of STAT3/NF-kB-activating cytokines in the neoplastic areas. These data suggest that strategies aimed at the cotargeting of STAT3/NF-kB activation and interaction between them might represent an attractive and novel approach to combat CRC.

Background & Aims T cells mediate the development of inflammation in inflammatory bowel disease (IBD). We investigated the effects of an antibody against CD3 called otelixizumab, which induces immune tolerance, in intestinal mucosa samples from patients. Methods Intestinal tissues were isolated from patients undergoing routine endoscopy or from patients undergoing intestinal surgery for colon cancer or IBD; healthy surrounding tissues were collected as controls. Isolated lamina propria mononuclear cells (LPMCs) and mucosal tissue explants were incubated with otelixizumab for 24 or 48 hours. Production of inflammatory cytokines was determined by enzyme-linked immunosorbent assay. Levels of 36 cytokines and chemokines and phosphorylation of 39 receptor tyrosine kinases and signaling molecules were measured using protein arrays. Immunoblot analysis was used to analyze T-cell transcription factors. Results Incubation of intestinal tissues or LPMCs with otelixizumab reduced production of interferon gamma, interleukin (IL)-17A, and other inflammatory cytokines and chemokines, simultaneously increasing production of IL-10. Mucosal biopsy specimens from patients with IBD retained inflammation-associated tyrosine phosphoprotein profiles ex vivo. Incubation of the inflamed tissue with otelixizumab reduced phosphorylation of these proteins to levels observed in control tissues. Otelixizumab also markedly reduced phosphorylation of proteins associated with T-cell receptor activation. Neutralization of IL-10 blocked the anti-inflammatory effects of otelixizumab. Conclusions We observed anti-inflammatory effects of anti-CD3 in inflamed intestinal tissues from patients with IBD. The antibody appears to down-regulate T-cell activation via IL-10.

In recent years, there have been significant advances in our understanding of the mucosal immune system. In addition to unravelling some of the complexities of this system, including the discovery of completely new cells types, further insights into the three-way interactions between mucosal immune cells, the intestinal epithelium and the microbial communities colonizing the GI tract promise to redefine our understanding of how intestinal homeostasis is maintained, but also how dysregulation of these highly integrated interactions conspires to cause disease. In this review, we will discuss major recent advances in the role of key immune players in the gut, including innate lymphoid cells (ILCs), mucosa-associated invariant T cells (MAIT cells) and cells of the mononuclear phagocyte system (MPS), including how these cells interact with the intestinal epithelial and their crosstalk with components of the intestinal microbiota, and how these interactions shape host health.

In nonhuman primates, Vγ9Vδ2+ (Vδ2)T cells proliferate and accumulate in mucosal tissues following microbial activation. Human Vδ2T cells produce proinflammatory cytokines in response to bacterial species that colonize the gut, but the role played by Vδ2T cells in intestinal immunity is unknown. We hypothesized that circulating Vδ2T cells can populate the human intestine and contribute to mucosal inflammation. Cell suspensions prepared from peripheral blood and intestinal biopsies were stimulated with microbial phosphoantigen (1-hydroxy-2-methyl-2-buten-4-yl 4-diphosphate [HDMAPP]) and analyzed by flow cytometry to determine Vδ2T cell phenotype, cytokine production, and proliferative potential. Circulating Vδ2T cells expressed gut-homing integrin α4β7 (>70%), which was coexpressed with skin-associated cutaneous leukocyte Ag by up to 15% of the total population. However, Vδ2T cell activation with HDMAPP and exposure to retinoic acid (signaling via retinoic acid receptor α) increased α4β7 expression and enhanced binding to mucosal addressin cell adhesion molecule-1 in vitro while simultaneously suppressing cutaneous leukocyte Ag, thereby generating a committed gut-tropic phenotype. Confocal microscopy and flow cytometry identified frequent Vδ2T cells that migrated out of human intestinal biopsies and comprised both CD103+ and CD103− subsets that produced TNF-α and IFN-γ upon phosphoantigen exposure, with more frequent cytokine-producing cells in the CD103− population. Activated intestinal Vδ2T cells expressed CD70 and HLA-DR but were unable to drive the proliferation of allogeneic naive CD4+ T cells. Instead, phosphoantigen-activated CD103− Vδ2T cells increased T-bet expression and enhanced IFN-γ production by autologous colonic αβ T cells via an IFN-γ–dependent mechanism. These data demonstrate that circulating Vδ2T cells display enhanced gut-homing potential upon microbial activation and populate the human intestinal mucosa, generating functionally distinct CD103+ and CD103− subsets that can promote inflammation by colonic αβ T cells.

Fulminant hepatitis (FH) is a disease characterized by massive destruction of hepatocytes with severe impairment of liver function. The pathogenesis of FH is not fully understood, but hyperactivity of T cells and macrophages with excessive production of cytokines are important hallmarks of the condition. In this study, we investigated the role of interleukin (IL)−25 in FH. IL-25 expression was evaluated in patients with FH and in livers of mice with FH induced by D-galactosamine (D-Gal) and lipopolysaccharide (LPS). Mice were treated with IL-25 before D-Gal/LPS-induced FH and before or after concanavalin A (ConA)-induced FH. Mononuclear cells were isolated from livers of mice treated with or without IL-25 and analyzed for GR1+CD11b+ cells. CFSE-labeled T cells were cocultured with GR1+CD11b+ cells and their proliferation was evaluated by flow cytometry. Mice were also treated with a depleting anti-GR1 antibody before IL-25 and D-Gal/LPS administration. IL-25 was constitutively expressed in mouse and human liver and down-regulated during FH. IL-25 prevented D-Gal/LPS-induced FH and this effect was associated with increased infiltration of the liver with cells coexpressing GR1 and CD11b. In vitro studies showed that GR1+CD11b+ cells isolated from mice given IL-25 inhibited T-cell proliferation. Consistently, in vivo depletion of GR1+ cells abrogated the protective effect of IL-25 in experimental D-Gal/LPS-induced FH. IL-25 was both preventive and therapeutic in ConA-induced FH. Conclusions: IL-25 expression is markedly reduced during human and experimental FH. IL-25 promotes liver accumulation of GR1+CD11b+cells with immunoregulatory properties. (Hepatology 2013;58:1436–1450)

Objective Cryptogenic multifocal ulcerating stenosing enteritis (CMUSE) is an extremely rare, but devastating, disease of unknown aetiology. We investigated the genetic basis of this autosomal recessive condition in a pair of affected siblings who have 40-year histories of catastrophic gastrointestinal and extraintestinal disease. Design Genome-wide single-nucleotide polymorphism homozygosity mapping in the two affected family members combined with whole-exome sequencing of one affected sibling. This was followed by confirmatory Sanger sequencing of the likely disease-causing sequence variant and functional studies in affected and unaffected family members. Results Insertion/deletion variation analysis revealed the presence of a homozygous 4 bp deletion (g.155574_77delGTAA) in the PLA2G4A gene, located in the splice donor site directly after exon 17 (the penultimate exon) of the gene in both affected siblings. This introduces a frameshift of 10 amino acids before a premature stop codon (p.V707fsX10), which is predicted to result in the loss of 43 amino acids (residues 707–749) at the C-terminus of cytosolic phospholipase A2-α (cPLA 2 α). cPLA 2 α protein expression was undetectable in the gut of both siblings, with platelet aggregation and thromboxane A 2 production, as functional assays for cPLA 2 α activity, grossly impaired. Conclusions We have identified mutations in PLA2G4A as a cause of CMUSE in two affected siblings. Further studies are needed to determine if mutations in this gene are also responsible for disease of a similar phenotype in other cases.

Objectives: This review article describes the role of neutrophils in mucosal injury and the resulting crypt abscesses characteristic of ulcerative colitis. We also review selected biomarkers for monitoring neutrophil presence and activity in the mucosa as well as their potential as therapeutic targets. Material: We have collated and selectively reviewed data on the most prominent well-established and emerging neutrophil-related biomarkers and potential therapeutic targets (calprotectin, lactoferrin, CXCR1, CXCR2, MMP-9, NGAL, elafin, HNE, pANCAs, MPO, CD16, CD177, CD64, HNPs, SLPI and PTX3) in ulcerative colitis. Results: Systemic and intestinal neutrophil activity increases substantially in active ulcerative colitis, driving tissue damage and extra-intestinal manifestations. Calprotectin is a robust neutrophil and disease biomarker, and a few neutrophil-related targets are being clinically explored as therapeutic targets. Conclusion: We propose that targeting neutrophils and their inflammatory mediators per se is an opportunity that should be explored to identify new effective medical therapies. The overall clinical goal for neutrophil-targeted therapy will be to modulate, but not completely silence, neutrophil activity, thereby abolishing the destructive inflammation with associated acute and chronic tissue damage without compromising host-defense.

Infection of mice with the intestinal bacterial pathogenCitrobacter rodentiumresults in colonic mucosal hyperplasia and a local Th1 inflammatory response similar to that seen in mouse models of inflammatory bowel disease. In these latter models, and in patients with Crohn's disease, neutralization of tumor necrosis factor alpha (TNF-α) is of therapeutic benefit. Since there is no information on the role of TNF-α in either immunity to noninvasive bacterial pathogens or on the role of TNF-α in the immunopathology of infectious colitis, we investigatedC. rodentiuminfection in TNFRp55−/−mice. In TNFRp55−/−mice, there were higher colonic bacterial burdens, but the organisms were cleared at the same rate as C57BL/6 mice, showing that TNF-α is not needed for protective antibacterial immunity. The most striking feature of infection in TNFRp55−/−mice, however, was the markedly enhanced pathology, with increased mucosal weight and thickness, increased T-cell infiltrate, and a markedly greater mucosal Th1 response. Interleukin-12 p40 transcripts were markedly elevated inC. rodentium-infected TNFRp55−/−mice, and this was associated with enhanced mucosal STAT4 phosphorylation. TNF-α is not obligatory for protective immunity toC. rodentiumin mice; however, it appears to play some role in downregulating mucosal pathology and Th1 immune responses.

Mice infected with Citrobacter rodentium represent an excellent model in which to examine immune defenses against an attaching-effacing enteric bacterial pathogen. Colonic tissue from mice infected with C. rodentium harbors increased transcripts for IL-12 and IFN-γ and displays mucosal pathology compared with uninfected controls. In this study, the role of IL-12 and IFN-γ in host defense and mucosal injury during C. rodentium infection was examined using gene knockout mice. IL-12p40−/− and IFN-γ−/− mice were significantly more susceptible to mucosal and gut-derived systemic C. rodentium infection. In particular, a proportion of IL-12p40−/− mice died during infection. Analysis of the gut mucosa of IL-12p40−/− mice revealed an influx of CD4+ T cells and a local IFN-γ response. Infected IL-12p40−/− and IFN-γ−/− mice also mounted anti-Citrobacter serum and gut-associated IgA responses and strongly expressed inducible NO synthase (iNOS) in mucosal tissue, despite diminished serum nitrite/nitrate levels. However, iNOS does not detectably contribute to host defense against C. rodentium, as iNOS−/− mice were not more susceptible to infection. However, C57BL/6 mice infected with C. rodentium up-regulated expression of the mouse β-defensin (mBD)-1 and mBD-3 in colonic tissue. In contrast, expression of mBD-3, but not mBD-1, was significantly attenuated during infection of IL-12- and IFN-γ-deficient mice, suggesting mBD-3 may contribute to host defense. These studies are among the first to examine mechanisms of host resistance to an attaching-effacing pathogen and show an important role for IL-12 and IFN-γ in limiting bacterial infection of the colonic epithelium.

Summary Mice lacking the transcription factor T-bet in the innate immune system develop microbiota-dependent colitis. Here, we show that interleukin-17A (IL-17A)-producing IL-7Rα+ innate lymphoid cells (ILCs) were potent promoters of disease in Tbx21−/−Rag2−/− ulcerative colitis (TRUC) mice. TNF-α produced by CD103−CD11b+ dendritic cells synergized with IL-23 to drive IL-17A production by ILCs, demonstrating a previously unrecognized layer of cellular crosstalk between dendritic cells and ILCs. We have identified Helicobacter typhlonius as a key disease trigger driving excess TNF-α production and promoting colitis in TRUC mice. Crucially, T-bet also suppressed the expression of IL-7R, a key molecule involved in controlling intestinal ILC homeostasis. The importance of IL-7R signaling in TRUC disease was highlighted by the dramatic reduction in intestinal ILCs and attenuated colitis following IL-7R blockade. Taken together, these data demonstrate the mechanism by which T-bet regulates the complex interplay between mucosal dendritic cells, ILCs, and the intestinal microbiota., Highlights ► Chronic colitis in TRUC mice was mediated by IL-17-producing innate lymphoid cells ► TNF-α synergized with IL-23 to induce innate IL-17 production ► Helicobacter typhlonius triggered intestinal pathology in TRUC mice ► T-bet regulated IL-7R transcription, a key checkpoint in intestinal ILC homeostasis

Serine proteases, cysteine proteases, aspartic proteases and matrix metalloproteinases play an essential role in extracellular matrix remodeling and turnover through their proteolytic action on collagens, proteoglycans, fibronectin, elastin and laminin. Proteases can also act on chemokines, receptors and anti-microbial peptides, often potentiating their activity. The intestinal mucosa is the largest interface between the external environment and the tissues of the human body and is constantly exposed to proteolytic enzymes from many sources, including bacteria in the intestinal lumen, fibroblasts and immune cells in the lamina propria and enterocytes. Controlled proteolytic activity is crucial for the maintenance of gut immune homeostasis, for normal tissue turnover and for the integrity of the gut barrier. However, in intestinal immune-mediated disorders, pro-inflammatory cytokines induce the up-regulation of proteases, which become the end-stage effectors of mucosal damage by destroying the epithelium and basement membrane integrity and degrading the extracellular matrix of the lamina propria to produce ulcers. Protease-mediated barrier disruption in turn results in increased amounts of antigen crossing into the lamina propria, driving further immune responses and sustaining the inflammatory process.

Regulatory T cells (CD4+CD25hiCD127loFOXP3+ T cells [Tregs]) are a population of lymphocytes involved in the maintenance of self-tolerance. Abnormalities in function or number of Tregs are a feature of autoimmune diseases in humans. The ability to expand functional Tregs ex vivo makes them ideal candidates for autologous cell therapy to treat human autoimmune diseases and to induce tolerance to transplants. Current tests of Treg function typically take up to 120 hours, a kinetic disadvantage as clinical trials of Tregs will be critically dependent on the availability of rapid diagnostic tests before infusion into humans. Here we evaluate a 7-hour flow cytometric assay for assessing Treg function, using suppression of the activation markers CD69 and CD154 on responder T cells (CD4+CD25− [Tresp]), compared with traditional assays involving inhibition of CFSE dilution and cytokine production. In both freshly isolated and ex vivo expanded Tregs, we describe excellent correlation with gold standard suppressor cell assays. We propose that the kinetic advantage of the new assay may place it as the preferred rapid diagnostic test for the evaluation of Treg function in forthcoming clinical trials of cell therapy, enabling the translation of the large body of preclinical data into potentially useful treatments for human diseases.

Purpose of review The aryl hydrocarbon receptor (AhR), a transcription factor activated by a large number of environmental agents, modulates the activity of immune and nonimmune cells in the gut, and may represent an important link between the environment and the immune perturbations which underlie the pathogenesis of inflammatory bowel disease. This review will summarize the current knowledge of the role of AhR in regulation of intestinal immune homeostasis and inflammation. Recent findings Activation of AhR by dietary ligands is necessary for the maintenance or expansion of innate immune cells in the gut, such as intraepithelial lymphocytes (IELs) and interleukin (IL)-22-producing lymphoid cells (ILC22). AhR-deficient mice lack IELs, have reduced number of ILC22 cells, and are more susceptible to bacterial infections and experimental colitis. In animal models, AhR activators inhibit proinflammatory cytokine synthesis and attenuate colitis by a pathway that involves IL-22. Analysis of AhR in the human gut reveals that intestinal T cells and natural killer cells isolated from Crohn's disease patients express low levels of AhR and respond to AhR ligands by downregulating inflammatory cytokines and upregulating IL-22. Summary These novel findings may help explain how environmental factors may regulate mucosal immune responses.

Activation of cannabinoid receptors (CBs) by endocannabinoids impacts on a number of gastrointestinal functions. Recent data indicate that CB1 agonists improve 2,4-dinitrobenzene sulfonic acid-induced colitis in mice, thus suggesting a role for the endocannabinoid agonist anandamide (AEA) in protecting the gut against inflammation. We here examined the gut endocannabinoid system in inflammatory bowel disease (IBD) patients, and investigated the ex vivo and in vitro effects of the non-hydrolysable AEA analog methanandamide (MAEA) on the mucosal proinflammatory response. The content of AEA, but not of 2-arachidonoyl-glycerol and N-palmitoylethanolamine, was significantly lower in inflamed than uninflamed IBD mucosa, and this was paralleled by lower activity of the AEA-synthesizing enzyme N-acyl-phosphatidylethanolamine-specific phospholipase D and higher activity of the AEA-degrading enzyme fatty acid amide hydrolase. MAEA significantly downregulated interferon-γ and tumor necrosis factor-α secretion by both organ culture biopsies and lamina propria mononuclear cells. Although these results are promising, further studies are needed to determine the role of cannabinoid pathways in gut inflammation. © 2011 Society for Mucosal Immunology.

IL-15 has a broad spectrum of biological activities. It is crucial for the development, proliferation, survival and differentiation of multiple cells from both innate and adaptive immune systems. However, IL-15 up-regulation has a central role in the development of several autoimmune or chronic inflammatory disorders. Therefore, targeting IL-15 or its receptor may have a valuable impact on the treatment of immune-mediated diseases. On the other hand, in some infectious diseases, IL-15 production is compromised but IL-15 given exogenously can potentially enhance immune responses to pathogens. Here, we discuss the current understanding of IL-15 role in immune-mediated and infectious diseases as well as its therapeutic use.

The immune system faces the arduous task of defending the mucosal surfaces from invading pathogens, but must simultaneously repress responses against commensal organisms and other inert antigens that are abundant in the external environment, as inappropriate immune activation might expose the host to increased risk of autoimmunity. The behavior of individual immune cells is governed by the expression of transcription factors that are responsible for switching immune response genes on and off. T-bet (T-box expressed in T cells) has emerged as one of the key transcription factors responsible for controlling the fate of both innate and adaptive immune cells, and its expression in different immune cells found at mucosal surfaces is capable of dictating the critical balance between permitting robust host immunity and limiting susceptibility to autoimmunity and allergy.

Background: We previously demonstrated that in inflammatory bowel disease (IBD) there is enhanced production of interleukin (IL)-21, a cytokine that activates multiple pathways that sustain mucosal inflammation. However, the phenotype of IL-21-producing cells in IBD, and the cytokine(s) they coproduce, is not known. We here characterized the cell source of IL-21 and determined which factors regulate IL-21 in the human gut. Methods: Cytokines were analyzed in CD4+ T intestinal lamina propria lymphocytes (T-LPL) isolated from IBD patients and controls by flow cytometry. Moreover, IL-21 was evaluated in mucosal T follicular cells (TFH). To assess the involvement of IL-12 and IL-23 in the production of IL-21, T-LPL were activated in the presence or absence of IL-12 or IL-23. Results: The proportion of IL-21-producing CD4+ T-LPL was increased in IBD compared to controls. The majority of IL-21-producing T-LPL coexpressed interferon (IFN)-γ, and to a lesser extent IL-4 or IL-17A. Activation of CD4+ T-LPL with IL-12 but not IL-23 enhanced the fraction of cells coexpressing IL-21 and IFN-γ. TFH cells in LPL were identified by CXCR5 expression and expressed IL-21 both in IBD and controls; however, the fraction of IL-21-positive TFH cells was higher in Crohn's disease than in ulcerative colitis and controls. Treatment of CD4+ T-LPL with IL-12 enhanced the frequency of CXCR5+ IL-21-producing TFH cells. Conclusions: These findings indicate that in IBD IL-21 is mostly produced by CD4+ T-LPL coexpressing IFN-γ, reinforcing the concept that distinct subsets of T cells can produce IL-21. Inflamm Bowel Dis 2010

Evaluation of: Nava P, Koch S, Laukoetter MG et al. Interferon-γ regulates intestinal epithelial homeostasis through converging β-catenin signaling pathways. Immunity 32(3), 392–402 (2010).Inflammation in the gut is associated with changes in the epithelial layer. Barrier function is diminished, epithelial cell death may occur and the epithelial cells themselves secrete proinflammatory cytokines. One of the most obvious changes, however, is in the rate of epithelial renewal, which most often manifests as increased epithelial proliferation, with an increase in mucosal thickness in the colon and the length of the crypts of Lieberkuhn in the small bowel. The factors that control the basal rate of renewal and the epithelial stem cell niche have been well studied and it is clear that Wnt signaling is critically important. Inflammatory cytokines, therefore, may alter epithelial renewal in the gut by modifying or antagonizing Wnt signaling pathways.

Interleukin (IL)-21, a cytokine mostly produced by activated CD4+ T cells, has been reported to play an important role in the tissue-damaging immune response in various organs. This pathogenic effect is strictly linked to the ability of IL-21 to control the functional activities of multiple immune and non-immune cells. For instance, IL-21 regulates the differentiation and function of effector CD4+ T helper cells; controls activation, proliferation, and survival of B cells and enhances the cytotoxic activity of CD8+ T cells and NK cells. IL-21 also inhibits the differentiation of inducible regulatory T cells (Tregs) and makes effector CD4+ T cells resistant to the Tregs-mediated immunesuppression. Additionally, IL-21 stimulates epithelial cells and fibroblasts to make chemokines and extracellular matrix proteases, respectively. Consistently, studies from various laboratories have documented the beneficial effect of IL-21 neutralization on the progression of inflammatory diseases in mice. Here we review the present knowledge on the expression and role of IL-21 in immune-mediated pathologies.

Background & Aims Mesalamine has been reported to protect against inflammatory bowel disease–related colorectal cancer (CRC), but several drug-related issues have limited its use in chemopreventive programs. We evaluated the antineoplastic properties of mesalamine derivatives using in vitro and in vivo models of CRC. Methods CRC cell proliferation and cell-cycle progression were evaluated by flow cytometry after exposure to mesalamine or mesalamine derivatives. Cyclins, cyclin-dependent kinases, and endoplasmic reticulum stress–related molecules were examined by immunoblotting. The in vivo antineoplastic effect of 2-methoxy-5-amino-N-hydroxybenzamide (2-14) was evaluated in a syngenic, CT26-derived xenograft mouse model of CRC and in the azoxymethane/dextran sulfate sodium–induced mouse model of colitis-associated CRC. Results The mesalamine derivative 2-14 was 10-fold more potent than mesalamine in inhibiting CRC cell proliferation. After exposure to 2-14, cyclin D1 expression was reduced and G0/G1 phase cells accumulated. These events were preceded by activation of eukaryotic translation initiation factor 2-alpha kinase 3 (pancreatic endoplasmic reticulum eIF2α kinase), phosphorylation of eukaryotic translation initiation factor 2alpha, induction of activating transcription factor 4, and splicing of X-box binding protein 1 messenger RNA, events that define endoplasmic reticulum stress. Silencing of PERK restored cyclin D1 levels, allowing cells to overcome the cell-cycle block induced by 2-14. Mice injected with 2-14 developed fewer CRC xenograft-derived tumors. Moreover, 2-14 injection reduced the development of neoplastic lesions induced by azoxymethane and dextran sulfate sodium in mice. Conclusions The mesalamine derivative 2-14 inhibited CRC cell proliferation in vitro and prevented CRC progression in mouse models.

Mucosal addressin cell adhesion molecule 1, expressed on gut endothelial cells, in conjunction with integrin alpha(4)beta(7), expressed on lymphocytes, is critical in lymphocyte homing to the gut. The mucosal addressin cell adhesion molecule 1/integrin alpha(4)beta(7) pathway is involved in the pathogenesis of chronic intestinal inflammation by recruiting lymphocytes into inflamed gut. We explored the duodenal expression of mucosal addressin cell adhesion molecule 1 and the peripheral T-cell expression of integrin alpha(4)beta(7) in patients with celiac disease. Duodenal biopsies and a peripheral blood sample were collected from 15 celiac patients, before and after 12 months of gluten-free diet, and from 12 control subjects. Treated celiac biopsies were cultured with peptic-tryptic digest of gliadin and/or an anti-interferon alpha neutralizing antibody. Mucosal addressin cell adhesion molecule 1 was determined by confocal immunofluorescence microscopy and immunoblotting. Integrin beta(7)-positive T cells were analyzed by flow cytometry. Mucosal addressin cell adhesion molecule 1 expression was significantly higher in active celiac disease than in normal mucosa. After gluten-free diet, a dramatic reduction of mucosal addressin cell adhesion molecule 1 was also observed. No difference was seen between patients with celiac disease after treatment and controls. Ex vivo peptic-tryptic digest of gliadin challenge induced a marked increase of mucosal addressin cell adhesion molecule 1 expression. Blocking interferon alpha inhibited the peptic-tryptic digest of gliadin-induced mucosal addressin cell adhesion molecule 1 overexpression. The percentage of circulating beta(7)-positive T cells was significantly lower in untreated celiac disease in comparison to controls but normalized after gluten-free diet. Mucosal addressin cell adhesion molecule 1 is strongly up-regulated in active celiac disease dependent on interferon alpha and is associated with peripheral depletion of integrin alpha(4)beta(7)-expressing T cells. We conclude that mucosal addressin cell adhesion molecule 1 may represent an important determinant for the generation of mucosal damage in celiac disease.

Background and Aims: In addition to its crucial role in dampening tissue-damaging immune responses in the gut, transforming growth factor β (TGFβ) is a potent profibrogenic agent inducing collagen synthesis and regulating the balance between matrix-degrading matrix metalloproteinases (MMPs) and their inhibitors (TIMPs). TGFβ signalling was investigated by analysis of Smad proteins and MMPs/TIMPs in the mucosa overlying strictures in patients with Crohn’s disease (CD). Methods: Specimens were collected from macroscopically normal mucosa overlying strictured and non-strictured gut of patients with fibrostenosing CD. Isolated myofibroblasts were cultured with anti-TGFβ blocking antibody or TGFβ1. TGFβ transcripts were analysed by quantitative reverse transcription-PCR (RT-PCR). Smad proteins and MMPs were determined by immunoblotting. MMP-12 activity was measured by a real-time MMP-12 activity assay. An in vitro wound-healing scratch assay was used to assess myofibroblast migration. Results: TGFβ transcripts, phosphorylated Smad2–Smad3 (pSmad2–3) and TIMP-1 proteins were higher in mucosa overlying strictures than in mucosa overlying non-strictured areas. In contrast, mucosa overlying strictured gut had lower expression of Smad7, MMP-12 and MMP-3. Myofibroblasts from mucosa overlying strictured gut showed higher TGFβ transcripts, a greater pSmad2–3 response to TGFβ, increased TIMP-1, lower Smad7, increased collagen production and reduced migration ability compared with myofibroblasts from mucosa overlying non-strictured gut. TGFβ blockade increased myofibroblast MMP-12 production and migration, more obviously in myofibroblasts isolated from mucosa overlying non-strictured compared with strictured gut. Conclusions: Changes in TGF-β signalling and MMP production were identified in the mucosa overlying strictures in CD which may give a window into the process of fibrosis.

Citrobacter rodentium, a natural mouse pathogen, belongs to the family of extracellular enteric pathogens that includes enteropathogenicEscherichia coli(EPEC) and enterohemorrhagicE. coli(EHEC).C. rodentiumshares many virulence factors with EPEC and EHEC and relies on attaching-and-effacing lesion formation for colonization and infection of the gut. In vivo,C. rodentiuminfection is characterized by increased epithelial cell proliferation, mucosal thickening, and a TH1-type immune response, but with protective immunity believed to be mediated by serum immunoglobulin G (IgG). In this work, we characterize the immune response and pathology of mice lacking the p50 subunit of the transcription factor nuclear factor kappa B (NF-κB) duringC. rodentiuminfection. We show that p50−/−mice are unable to clearC. rodentiuminfection. Furthermore, these animals show a reduced influx of immune cells into infected colonic tissue and greater levels of mucosal hyperplasia and the cytokines tumor necrosis factor alpha and gamma interferon. Surprisingly, despite being unable to eliminate infection, p50−/−mice showed markedly higher levels of anti-CitrobacterIgG and IgM, suggesting that antibody alone is not responsible for bacterial clearance. These data also demonstrate that non-NF-κB-dependent defenses are insufficient to controlC. rodentiuminfection, and hence, the NF-κB p50 subunit is critical for defense against this noninvasive pathogen.

Naive T cells can commit to effector [T helper 1 (Th1), Th2 and Th17] or regulatory lineages. Skewing of responses toward inflammatory Th1, Th2 or Th17 pathways and away from regulatory T-cell pathways might be responsible for the initiation and progress of immune-mediated diseases. Based on recent data, we propose that interleukin-21 (IL-21), a cytokine produced by activated CD4 + T cells, induces the development of Th17 cells, blocks the differentiation of transforming growth factor-β1–induced regulatory T cells and renders CD4 + T cells resistant to the suppressive effects of regulatory T cells, thereby playing a major role in pathogenic T-cell responses.

In healthy individuals, antigens from the gut lumen are tolerated by the mucosal immune system. However, a loss of tolerance toward the bacterial microflora probably causes inflammatory bowel disease (IBD), Crohn's disease (CD) and ulcerative colitis. The abnormal activation of the immune system in the gut of IBD patients is characterized by a cascade of cellular events orchestrated by cytokine cross talk between immune and non-immune cells. Interleukin (IL)-21, the newest member of the common gamma-chain-dependent cytokine family, is a key component of the inflammatory cascade in the gut. It is highly expressed in CD and sustains the ongoing T helper type 1 (Th1)-mediated immune response. IL-21 is essential for the differentiation of Th17 cells. IL-21 is also involved in recruiting T cells to the inflamed gut and eliciting the secretion of matrix-degrading enzymes by gut fibroblasts. Overall, there is now sufficient evidence to suggest that targeting IL-21 will be of therapeutic benefit in IBD.

Background: In coeliac disease (CD), the upper bowel lesion is associated with a marked infiltration of the mucosa with Th1 cells secreting interferon γ (IFNγ) and expressing the Th1-associated transcription factor, T-bet. However, the molecular mechanisms which regulate T-bet and promote the Th1 cell response are unknown. Objective: To examine whether interleukin 21 (IL21), a cytokine that regulates T cell activation, has a role in CD. Methods: Duodenal mucosal samples were taken from CD patients and normal controls. IL21 and T-bet were examined by real-time PCR and western blotting, and IFNγ was assessed by real-time PCR and ELISA. The effect of blockade of endogenous IL21 on the expression of T-bet was examined in an ex vivo culture of biopsies taken from untreated CD patients. Finally, the role of IL21 in controlling T-bet and IFNγ was also evaluated in cultures of biopsies taken from treated CD patients and cultured with a peptic–tryptic digest of gliadin (PT) in the presence or absence of a neutralising IL21 antibody. Results: Enhanced IL21 RNA and protein expression was seen in duodenal samples from untreated CD patients. Blockade of IL21 activity in biopsies of untreated CD patients reduced T-bet and IFNγ secretion. Stimulation of treated CD biopsies with PT enhanced IL21 expression, and neutralisation of IL21 largely prevented PT-driven T-bet and IFNγ induction. Conclusions: IL21 is overproduced in the mucosa of CD patients, where it helps sustain T-bet expression and IFNγ production.

Helicobacter pylori (Hp) infection is associated with a marked infiltration of the gastric mucosa by inflammatory cells. The molecular pathways that control Hp-associated inflammatory reaction are complex, but locally induced cytokines seem to contribute to maintaining the ongoing inflammation. We have previously shown that IL-17 is over-produced in Hp-infected gastric mucosa, and that IL-17 stimulates the synthesis of IL-8, the major neutrophil chemoattractant. Factors/mechanisms that regulate IL-17 expression remain, however, unknown. In this study, we initially expanded our previous data, showing that CD4(+) and CD8(+) T cells are a source of IL-17 in Hp-infected samples. Since IL-23 enhances T cell-derived IL-17 during bacterial infections, we then assessed the role of IL-23 in controlling IL-17 expression in Hp-colonized stomach. Using real-time PCR and ELISA, IL-23 was detected in all gastric biopsies, but its expression was more pronounced in Hp-infected samples in comparison to controls. Treatment of normal gastric lamina propria mononuclear cells (LPMC) with IL-23 enhanced Stat3 activation and IL-17 secretion, and pharmacological inhibition of Stat3 prevented IL-23-driven IL-17 synthesis. Consistently, blockade of IL-23 in cultures of LPMC from Hp-infected patients reduced Stat3 activation and IL-17 production. Data show that IL-23 is overexpressed in Hp-infected gastric mucosa where it could contribute to sustaining IL-17 production.

Regulatory T (T(reg)) cells play a key role in the maintenance of the immune system homeostasis. T(reg) cells can be generated in the periphery under control of TGF-beta, a cytokine involved in the negative control of the immune system. However, TGF-beta cooperates with IL-6 in the generation of Th17 cells, a novel class of effector cells involved in numerous inflammatory diseases, including colitis. Therefore, TGF-beta emerges as a mediator of both anti-inflammatory and pro-inflammatory processes, depending on the local cytokine milieu. Here we demonstrate that IL-21, a type-1 cytokine produced by T cells and involved in the pathogenesis of immune-mediated diseases, prevents the TGF-beta-dependent expression of FoxP3, the master regulator of T(reg) cell commitment, and the induction of suppressive capacity in naive CD4(+) T cells, while promoting the differentiation of Th17 cells. In vivo, CD4(+) naive T cells activated in the presence of TGF-beta and IL-21 failed to suppress colitis while inducing an inflammatory response characterized by high levels of IL-17 and RORgammat, the transcription factor expressed by Th17 cells. Therefore, IL-21 emerges as a key modulator of TGF-beta signaling, leading to the reciprocal differentiation of T(reg) and Th17 cells.

Helicobacter pylori (Hp) infection is associated with gastric inflammation and ulceration. The pathways of tissue damage in Hp-infected subjects are complex, but evidence indicates that T cell-derived cytokines enhance the synthesis of matrix metalloproteinases (MMP) that contribute to mucosal ulceration and epithelial damage. In this study, we have examined the role of the T cell cytokine IL-21 in Hp-infected gastric mucosa and evaluated whether IL-21 regulates MMP production by gastric epithelial cells. We show that IL-21 is constitutively expressed in gastric mucosa and is more abundant in biopsy specimens and purified mucosal CD3+ T cells from Hp-infected patients compared with normal patients and disease controls. We also demonstrate that IL-21R is expressed by primary gastric epithelial cells, as well as by the gastric epithelial cell lines AGS and MKN28. Consistently, AGS cells respond to IL-21 by increasing production of MMP-2 and MMP-9, but not MMP-1, MMP-3, MMP-7, or tissue inhibitors of MMP. Analysis of signaling pathways leading to MMP production reveals that IL-21 enhances NF-κB but not MAPK activation, and inhibition of NF-κB activation reduces IL-21-induced MMP-2 and MMP-9 production. Finally, we show that treatment of Hp-infected gastric explants with anti-IL-21 reduces epithelial cell-derived MMP-2 and MMP-9 production. These data indicate that IL-21 is overexpressed in Hp-infected gastric mucosa where it could contribute to increased epithelial gelatinase production.

High expression of IL-21 and/or IL-21R has been described in T cell-mediated inflammatory diseases characterized by defects of counterregulatory mechanisms. CD4+CD25+ regulatory T cells (Treg) are a T cell subset involved in the control of the immune responses. A diminished ability of these cells to inhibit T cell activation has been documented in immune-inflammatory diseases, raising the possibility that inflammatory stimuli can block the regulatory properties of Treg. We therefore examined whether IL-21 controls CD4+CD25+ T cell function. We demonstrate in this study that IL-21 markedly enhances the proliferation of human CD4+CD25− T cells and counteracts the suppressive activities of CD4+CD25+ T cells on CD4+CD25− T cells without affecting the percentage of Foxp3+ cells or survival of Treg. Additionally, CD4+CD25+ T cells induced in the presence of IL-21 maintain the ability to suppress alloresponses. Notably, IL-21 enhances the growth of CD8+CD25− T cells but does not revert the CD4+CD25+ T cell-mediated suppression of this cell type, indicating that IL-21 makes CD4+ T cells resistant to suppression rather than inhibiting CD4+CD25+ T cell activity. Finally, we show that IL-2, IL-7, and IL-15, but not IL-21, reverse the anergic phenotype of CD4+CD25+ T cells. Data indicate that IL-21 renders human CD4+CD25− T cells resistant to Treg-mediated suppression and suggest a novel mechanism by which IL-21 could augment T cell-activated responses in human immune-inflammatory diseases.

Background & Aims: Interleukin (IL)-21, a T-cell–derived cytokine, is produced in excess in inflammatory bowel diseases (IBD). The IL-21 receptor (IL-21R) is expressed by immune and nonimmune cells, raising the possibility that IL-21 has broad effects in gut inflammation. In this study we examined whether intestinal epithelial cells express IL-21R and respond to IL-21 in IBD. Methods: IL-21R was evaluated in intestinal samples of IBD patients and controls by immunohistochemistry and Western blotting. Intestinal epithelial cells were stimulated with IL-21, and cell-free supernatants were evaluated by a protein array and enzyme-linked immunosorbent assay. The effect of IL-21–treated epithelial cell supernatants on blood lymphocyte migration was assessed using a chemotaxis assay. Finally, we evaluated the effect of a neutralizing IL-21 antibody on MIP-3α synthesis in ex vivo organ cultures of IBD mucosal explants. Results: Constitutive expression of IL-21R was seen in intestinal epithelial cells, but was higher in IBD patients than in controls. Stimulation of intestinal epithelial cells with IL-21 resulted in enhanced phosphorylation of ERK1/2 and p38 and increased synthesis of macrophage inflammatory protein-3 alpha (MIP-3α), a T-cell chemoattractant. Inhibition of ERK1/2 but not p38 suppressed IL-21–induced MIP-3α production. IL-21–treated cell culture supernatants enhanced in vitro lymphocyte migration, and this effect was inhibited by anti-MIP-3α antibody. Treatment of IBD explants with anti–IL-21 reduced MIP-3α production. Conclusions: These data show that intestinal epithelial cells are a target of IL-21 and that IL-21 is involved in the cross-talk between epithelial and immune cells in the gut.

Innate lymphoid cells (ILCs) are a family of immune cells that selectively accumulate in mucosal tissues serving as sentinels at the vanguard of host protective immunity. However, they are also implicated as cellular mediators of immune-mediated diseases, most notably IBD. ILCs are subdivided into distinct lineages based on the expression of effector cytokines and master transcription factors that programme their differentiation and inflammatory behaviour. Strikingly, these subsets closely resemble CD4(+) T-cell lineages, including T helper (TH)1, TH2 and TH17 cells that are similarly implicated in immune-mediated diseases. However, ILCs that promote the maintenance of intestinal epithelial cells, mostly through production of IL-22, also exist. ILCs rapidly respond to environmental cues, including cytokines, metabolic signals and luminal bacteria. They are potent and immediate producers of key cytokines linked to IBD pathogenesis, including TNF, IL-17, IL-22 and IFN-γ. Some subsets are implicated as mediators of chronic intestinal inflammation, whereas others might provide protective functions. They are present in the gut of patients with IBD and, intriguingly, closer scrutiny of IBD susceptibility loci shows that many of these genes are either expressed by, or are intimately linked to, ILC function. Looking forward, targeting ILCs could represent a new IBD treatment paradigm.

// Veronica De Simone 1 , Giulia Ronchetti 1 , Eleonora Franze 1 , Alfredo Colantoni 1 , Angela Ortenzi 1 , Massimo C. Fantini 1 , Angelamaria Rizzo 1 , Giuseppe S. Sica 2 , Pierpaolo Sileri 2 , Piero Rossi 2 , Thomas T. MacDonald 3 , Francesco Pallone 1 , Giovanni Monteleone 1 and Carmine Stolfi 1 1 Department of Systems Medicine, University of Rome “Tor Vergata”, Rome, Italy 2 Department of Surgery, University of Rome “Tor Vergata”, Rome, Italy 3 Centre for Immunology and Infectious Disease, Blizard Institute of Cell and Molecular Science, Barts and the London School of Medicine and Dentistry, London, UK Correspondence to: Carmine Stolfi, email: // Keywords : Apc min/+ mice, STAT3, COX-2/PGE2, VEGF Received : September 22, 2014 Accepted : February 17, 2015 Published : March 12, 2015 Abstract Interleukin (IL)-21 triggers inflammatory signals that contribute to the growth of neoplastic cells in mouse models of colitis-associated colorectal cancer (CRC). Because most CRCs are sporadic and arise in the absence of overt inflammation we have investigated the role of IL-21 in these tumors in mouse and man. IL-21 was highly expressed in human sporadic CRC and produced mostly by IFN-γ-expressing T-bet/RORγt double-positive CD3+CD8- cells. Stimulation of human CRC cell lines with IL-21 did not directly activate the oncogenic transcription factors STAT3 and NF-kB and did not affect CRC cell proliferation and survival. In contrast, IL-21 modulated the production of protumorigenic factors by human tumor infiltrating T cells. IL-21 was upregulated in the neoplastic areas, as compared with non-tumor mucosa, of Apc min/+ mice, and genetic ablation of IL-21 in such mice resulted in a marked decrease of both tumor incidence and size. IL-21 deficiency was associated with reduced STAT3/NF-kB activation in both immune cells and neoplastic cells, diminished synthesis of protumorigenic cytokines (that is, IL-17A, IL-22, TNF-α and IL-6), downregulation of COX-2/PGE2 pathway and decreased angiogenesis in the lesions of Apc min/+ mice. Altogether, data suggest that IL-21 promotes a protumorigenic inflammatory circuit that ultimately sustains the development of sporadic CRC.

Citrobacter rodentium is a natural mouse pathogen related to enteropathogenic and enterohemorrhagic Escherichia coli . We have previously utilized bioluminescence imaging (BLI) to determine the in vivo colonization dynamics of C. rodentium . However, due to the oxygen requirement of the bioluminescence system and the colonic localization of C. rodentium , in vivo localization studies were performed using harvested organs. Here, we report the detection of bioluminescent C. rodentium and commensal E. coli during colonization of the gastrointestinal tract in intact living animals. Bioluminescence was dependent on intact blood circulation, suggesting that the colonic environment is not anaerobic but nanaerobic. In addition, BLI revealed that C. rodentium colonizes the rectum, a site previously unreported for this pathogen.

Background & Aims: The up-regulation of matrix metalloproteinases (MMPs) in the inflamed gut has mainly been associated with mucosal degradation and ulceration. However, their in vitro capacity to specifically cleave inflammatory mediators indicates that MMPs may have a profound immunoregulatory impact. We hypothesized that MMPs proteolytically modify intestinal epithelial chemokine signaling. Methods: Interleukin-1β–stimulated Caco-2 cells were exposed basolaterally to nanomolar concentrations of activated MMP-3 or cocultured with interleukin-1β–stimulated, MMP-producing, colonic myofibroblasts (CCD-18co). The conditioned media were subjected to chemotaxis assays. In addition, epithelial cells from patients with colitis were examined by real-time polymerase chain reaction, immunoblotting, and immunohistochemistry. Results: MMP-3 dose-dependently induced the neutrophil (up to 5-fold) but not monocyte chemoattractant capacity of Caco-2 cells. A similar Caco-2 chemotactic response was obtained in the Caco-2/CCD-18co cocultures. The principal mediator of these protease-related effects was identified as the potent neutrophil chemokine CXCL7 (neutrophil activating peptide 2), a proteolytic cleavage product of chemotactically inert platelet basic protein (PBP), not previously identified in the intestine. Antibodies against CXCL7 inhibited the MMP-induced chemotactic response by 84%, and PBP mRNA and protein were detected in stimulated Caco-2 but not in CCD-18co cells. Furthermore, PBP transcript and protein levels were low in the mucosa and in isolated epithelial cells from patients with Crohn's disease and from normal intestine but increased up to 13-fold in patients with ulcerative colitis. Conclusions: These findings identify a novel proinflammatory action of MMPs in inflammation and suggest that lamina propria myofibroblasts are required to achieve maximal intestinal epithelial immune activation.

The major classes of enteric bacteria harbour a conserved core genomic structure, common to both commensal and pathogenic strains, that is most likely optimized to a life style involving colonization of the host intestine and transmission via the environment. In pathogenic bacteria this core genome framework is decorated with novel genetic islands that are often associated with adaptive phenotypes such as virulence. This classical genome organization is well illustrated by a group of extracellular enteric pathogens, which includes enteropathogenic Escherichia coli (EPEC), enterohaemorrhagic E. coli (EHEC) and Citrobacter rodentium, all of which use attaching and effacing (A/E) lesion formation as a major mechanism of tissue targeting and infection. Both EHEC and EPEC are poorly pathogenic in mice but infect humans and domestic animals. In contrast, C. rodentium is a natural mouse pathogen that is related to E. coli, hence providing an excellent in vivo model for A/E lesion forming pathogens. C. rodentium also provides a model of infections that are mainly restricted to the lumen of the intestine. The mechanism's by which the immune system deals with such infections has become a topic of great interest in recent years. Here we review the literature of C. rodentium from its emergence in the mid-1960s to the most contemporary reports of colonization, pathogenesis, transmission and immunity.