Immune Profiling of Human Gut-Associated Lymphoid Tissue Identifies a Role for Isolated Lymphoid Follicles in Priming of Region-Specific Immunity.

The intestine contains some of the most diverse and complex immune compartments in the body. Here we describe a method for isolating human gut-associated lymphoid tissues (GALTs) that allows unprecedented profiling of the adaptive immune system in submucosal and mucosal isolated lymphoid follicles (SM-ILFs and M-ILFs, respectively) as well as in GALT-free intestinal lamina propria (LP). SM-ILF and M-ILF showed distinct patterns of distribution along the length of the intestine, were linked to the systemic circulation through MAdCAM-1+ high endothelial venules and efferent lymphatics, and had immune profiles consistent with immune-inductive sites. IgA sequencing analysis indicated that human ILFs are sites where intestinal adaptive immune responses are initiated in an anatomically restricted manner. Our findings position ILFs as key inductive hubs for regional immunity in the human intestine, and the methods presented will allow future assessment of these compartments in health and disease.

Investigating the Crime Scene-Molecular Signatures in Inflammatory Bowel Disease.

Inflammatory bowel diseases (IBD) are without cure and troublesome to manage because of the considerable diversity between patients and the lack of reliable biomarkers. Several studies have demonstrated that diet, gut microbiota, genetics and other patient factors are essential for disease occurrence and progression. Understanding the link between these factors is crucial for identifying molecular signatures that identify biomarkers to advance the management of IBD. Recent technological breakthroughs and data integration have fuelled the intensity of this research. This research demonstrates that the effect of diet depends on patient factors and gut microbial activity. It also identifies a range of potential biomarkers for IBD management, including mucosa-derived cytokines, gasdermins and neutrophil extracellular traps, all of which need further evaluation before clinical translation. This review provides an update on cutting-edge research in IBD that aims to improve disease management and patient quality of life.

Immune cell-derived signals governing epithelial phenotypes in homeostasis and inflammation.

The intestinal epithelium fulfills important physiological functions and forms a physical barrier to the intestinal lumen. Barrier function is regulated by several pathways, and its impairment contributes to the pathogenesis of inflammatory bowel disease (IBD), a chronic inflammatory condition affecting more than seven million people worldwide. Current treatment options specifically target inflammatory mediators and have led to improvement of clinical outcomes; however, a significant proportion of patients experience treatment failure. Pro-repair effects of inflammatory mediators on the epithelium are emerging. In this review we summarize current knowledge on involved epithelial pathways, identify open questions, and put recent findings into clinical perspective, and pro-repair effects. A detailed understanding of epithelial pathways integrating mucosal stimuli in homeostasis and inflammation is crucial for the development of novel, more targeted therapies.

Kinase Signaling in Colitis-Associated Colon Cancer and Inflammatory Bowel Disease.

Colorectal cancer is a known complication of chronic inflammation of the colon ("colitis-associated colon cancer"). Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract. Patients with IBD are at increased risk of colon cancer compared to the general population. Kinase signaling pathways play critical roles in both the inflammation and regulating cellular processes such as proliferation and survival that contribute to cancer development. Here we review the interplay of kinase signaling pathways (mitogen-activated protein kinases, cyclin-dependent kinases, autophagy-activated kinases, JAK-STAT, and other kinases) and their effects on colitis-associated colon cancer. We also discuss the role of JAK-STAT signaling in the pathogenesis of IBD and the therapeutic landscape of JAK inhibitors for the treatment of IBD.

Impact of fibre and red/processed meat intake on treatment outcomes among patients with chronic inflammatory diseases initiating biological therapy: A prospective cohort study.

Background: Biologic disease-modifying drugs have revolutionised the treatment of a number of chronic inflammatory diseases (CID). However, up to 60% of the patients do not have a sufficient response to treatment and there is a need for optimization of treatment strategies. Objective: To investigate if the treatment outcome of biological therapy is associated with the habitual dietary intake of fibre and red/processed meat in patients with a CID. Methods: In this multicentre prospective cohort study, we consecutively enrolled 233 adult patients with a diagnosis of Crohn's Disease, Ulcerative Colitis, Rheumatoid Arthritis (RA), Axial Spondyloarthritis, Psoriatic Arthritis and Psoriasis, for whom biologic therapy was planned, over a 3 year period. Patients with completed baseline food frequency questionnaires were stratified into a high fibre/low red and processed meat exposed group (HFLM) and an unexposed group (low fibre/high red and processed meat intake = LFHM). The primary outcome was the proportion of patients with a clinical response to biologic therapy after 14-16 weeks of treatment. Results: Of the 193 patients included in our primary analysis, 114 (59%) had a clinical response to biologic therapy. In the HFLM group (N = 64), 41 (64%) patients responded to treatment compared to 73 (56%) in the LFHM group (N = 129), but the difference was not statistically significant (OR: 1.48, 0.72-3.05). For RA patients however, HFLM diet was associated with a more likely clinical response (82% vs. 35%; OR: 9.84, 1.35-71.56). Conclusion: Habitual HFLM intake did not affect the clinical response to biological treatment across CIDs. HFLM diet in RA patients might be associated with better odds for responding to biological treatment, but this would need confirmation in a randomised trial. Trial registration: (clinicaltrials.gov), identifier [NCT03173144].

IBD metabonomics predicts phenotype, disease course, and treatment response.

Metabonomics in inflammatory bowel disease (IBD) characterizes the effector molecules of biological systems and thus aims to describe the molecular phenotype, generate insight into the pathology, and predict disease course and response to treatment. Nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry (MS), and integrated NMR and MS platforms coupled with multivariate analyses have been applied to create such metabolic profiles. Recent advances have identified quiescent ulcerative colitis as a distinct molecular phenotype and demonstrated metabonomics as a promising clinical tool for predicting relapse and response to treatment with biologics as well as fecal microbiome transplantation, thus facilitating much needed precision medicine. However, understanding this complex research field and how it translates into clinical settings is a challenge. This review aims to describe the current workflow, analytical strategies, and associated bioinformatics, and translate current IBD metabonomic knowledge into new potential clinically applicable treatment strategies, and outline future key translational perspectives.

Identification, isolation and analysis of human gut-associated lymphoid tissues.

Gut-associated lymphoid tissues (GALTs) comprise key intestinal immune inductive sites, including the Peyer's patches of the small intestine and different types of isolated lymphoid follicle (ILF) found along the length of the gut. Our understanding of human GALT is limited due to a lack of protocols for their isolation. Here we describe a technique that, uniquely among intestinal cell isolation protocols, allows identification and isolation of all human GALT, as well as GALT-free intestinal lamina propria (LP). The technique involves the mechanical separation of intestinal mucosa from the submucosa, allowing the identification and isolation of submucosal ILF (SM-ILF), LP-embedded mucosal ILF (M-ILF) and LP free of contaminating lymphoid tissue. Individual SM-ILF, M-ILF and Peyer's patch follicles can be subsequently digested for downstream cellular and molecular characterization. The technique, which takes 4-10 h, will be useful for researchers interested in intestinal immune development and function in health and disease.

Metabonomics in ulcerative colitis: diagnostics, biomarker identification, and insight into the pathophysiology.

Nuclear magnetic resonance (NMR) spectroscopy and appropriate multivariate statistical analyses have been employed on mucosal colonic biopsies, colonocytes, lymphocytes, and urine from patients with ulcerative colitis (UC) and controls in order to explore the diagnostic possibilities, define new potential biomarkers, and generate a better understanding of the pathophysiology. Samples were collected from patients with active UC (n = 41), quiescent UC (n = 33), and from controls (n = 25) and analyzed by NMR spectroscopy. Data analysis was carried out by principal component analysis and orthogonal-projection to latent structure-discriminant analysis using the SIMCA P+11 software package (Umetrics, Umea, Sweden) and Matlab environment. Significant differences between controls and active UC were discovered in the metabolic profiles of biopsies and colonocytes. In the biopsies from patients with active UC higher levels of antioxidants and of a range of amino acids, but lower levels of lipid, glycerophosphocholine (GPC), myo-inositol, and betaine were found, whereas the colonocytes only displayed low levels of GPC, myo-inositol and choline. Interestingly, 20% of inactive UC patients had similar profiles to those who were in an active state. This study demonstrates the possibilities of metabonomics as a diagnostic tool in active and quiescent UC and provides new insight into pathophysiologic mechanisms.

Intestinal barrier integrity and inflammatory bowel disease: Stem cell-based approaches to regenerate the barrier.

Disruption of normal barrier function is a fundamental factor in the pathogenesis of inflammatory bowel disease, which includes increased epithelial cell death, modified mucus configuration, altered expression and distribution of tight junction proteins, along with a decreased expression of antimicrobial peptides. Inflammatory bowel disease is associated with life-long morbidity for affected patients, and both the incidence and prevalence is increasing globally, resulting in substantial economic strain for society. Mucosal healing and re-establishment of barrier integrity are associated with clinical remission, as well as with an improved patient outcome. Hence, these factors are vital treatment goals, which conventionally are achieved by a range of medical treatments, although none are effective in all patients, resulting in several patients still requiring surgery at some point. Therefore, novel treatment strategies to accomplish mucosal healing and to re-establish normal barrier integrity in inflammatory bowel disease are warranted, and luminal stem cell-based approaches might have an intriguing potential. Transplantation of in vitro expanded intestinal epithelial stem cells derived either directly from mucosal biopsies or from directed differentiation of human pluripotent stem cells may constitute complementary treatment options for patients with mucosal damage, as intestinal epithelial stem cells are multipotent and may give rise to all epithelial cell types of the intestine. This review provides the reader with a comprehensive state-of-the-art overview of the intestinal barrier's role in healthy and diseased states, discussing the clinical application of stem cell-based approaches to accomplish mucosal healing in inflammatory bowel disease.

YAP/TAZ-Dependent Reprogramming of Colonic Epithelium Links ECM Remodeling to Tissue Regeneration.

Tissue regeneration requires dynamic cellular adaptation to the wound environment. It is currently unclear how this is orchestrated at the cellular level and how cell fate is affected by severe tissue damage. Here we dissect cell fate transitions during colonic regeneration in a mouse dextran sulfate sodium (DSS) colitis model, and we demonstrate that the epithelium is transiently reprogrammed into a primitive state. This is characterized by de novo expression of fetal markers as well as suppression of markers for adult stem and differentiated cells. The fate change is orchestrated by remodeling the extracellular matrix (ECM), increased FAK/Src signaling, and ultimately YAP/TAZ activation. In a defined cell culture system recapitulating the extracellular matrix remodeling observed in vivo, we show that a collagen 3D matrix supplemented with Wnt ligands is sufficient to sustain endogenous YAP/TAZ and induce conversion of cell fate. This provides a simple model for tissue regeneration, implicating cellular reprogramming as an essential element.

Upregulation of cIAP2 in regenerating colonocytes in ulcerative colitis.

It has been reported that colonocytes in ulcerative colitis (UC) upregulate anti-apoptotic cytoprotective pathways. An expression-profiling study of apoptosis-related genes suggested that the cellular inhibitor of apoptosis protein-2 (cIAP2) could be upregulated in epithelial cells in UC. The role of cIAP2 in active UC was therefore investigated. Fourteen patients with active UC and 12 control subjects who underwent routine colonoscopy for control of their disease or as part of their examination program for irritable bowel syndrome were included. cIAP1 and cIAP2 expression was investigated by polymerase chain reaction, Western blotting, and immunohistochemistry. The regulation and role of cIAP2 for apoptosis was further investigated in cell cultures. cIAP2, but not cIAP1, was upregulated during active UC in regenerative epithelial cells. A similar upregulation was found in cell lines stimulated with proinflammatory cytokines and was dependent on nuclear factor kappaB activation. Inhibition of cIAP2 increases the susceptibility of epithelial cells to Fas ligation. Inflammation during active UC thus causes an upregulation of cIAP2 in regenerating epithelium, which renders the cells less susceptible to Fas ligation. This might play a role in regeneration of the epithelium but might additionally be implicated in carcinogenesis of UC.

Culturing human intestinal stem cells for regenerative applications in the treatment of inflammatory bowel disease.

Both the incidence and prevalence of inflammatory bowel disease (IBD) is increasing globally; in the industrialized world up to 0.5% of the population are affected and around 4.2 million individuals suffer from IBD in Europe and North America combined. Successful engraftment in experimental colitis models suggests that intestinal stem cell transplantation could constitute a novel treatment strategy to re-establish mucosal barrier function in patients with severe disease. Intestinal stem cells can be grown in vitro in organoid structures, though only a fraction of the cells contained are stem cells with regenerative capabilities. Hence, techniques to enrich stem cell populations are being pursued through the development of multiple two-dimensional and three-dimensional culture protocols, as well as co-culture techniques and multiple growth medium compositions. Moreover, research in support matrices allowing for efficient clinical application is in progress. In vitro culture is accomplished by modulating the signaling pathways fundamental for the stem cell niche with a suitable culture matrix to provide additional contact-dependent stimuli and structural support. The aim of this review was to discuss medium compositions and support matrices for optimal intestinal stem cell culture, as well as potential modifications to advance clinical use in IBD.

Expression profiling of apoptosis-related genes in enterocytes isolated from patients with ulcerative colitis.

Apoptosis regulation has been implicated as a main cause of epithelial dysfunction in patients with ulcerative colitis. Apoptosis can be divided into distinct pathways, which depend on the expression of a large number of apoptosis-related genes. The aim was to elucidate which pathways are dominant in normal and inflamed colonic epithelial cells. An apoptosis-specific gene array expression profiling system of 96 genes was used to determine the expression profile of apoptosis-related genes. Epithelial cells isolated from three patients with active ulcerative colitis were pooled and compared to pooled epithelial cells isolated from three control subjects. Genes found to be three-fold or more overexpressed in ulcerative colitis were subsequently analysed by PCR in a larger population (10 patients with ulcerative colitis, 8 control subjects). Selected genes found not to be regulated were additionally tested by PCR in the same population. Six genes were found to be highly expressed in epithelial cells from both controls and ulcerative colitis patients. These included Bcl-2 antagonist/killer, B lymphoid tyrosine kinase, caspase 14, Harakiri, tumour necrosis factor (TNF) receptor 2, and TNF receptor-associated factor 1 (TRAF1). Three genes were found to be upregulated in ulcerative colitis (p<0.01): caspase 1 and 5, and inhibitor of apoptosis protein 2 (c-IAP2). Both receptor- and mitochondrion-dependent apoptosis pathways are well expressed in enterocytes. Mainly activation-dependent and cytoprotective genes were upregulated in ulcerative colitis.

Circulating Cytokines and Cytokine Receptors in Infliximab Treatment Failure Due to TNF-α Independent Crohn Disease.

The inflammatory response at infliximab (IFX) treatment failure due to tumor necrosis factor (TNF)-α-independent Crohn disease activity is unknown. This is an exploratory, hypothesis-generating study based on samples collected in a clinical trial among patients failing conventional IFX dosages and treated with an intensified IFX regimen for 12 weeks. Patients with clinical response at week 12, as defined by a reduction of Crohn disease activity index by ≥70, were considered to suffer from nonimmune pharmacokinetic (PK) treatment failure (n = 18), and nonresponders had a presumed pharmacodynamic (PD) failure due to non-TNF-driven disease (n = 8). Patients failing IFX due to functional anti-IFX antibodies (n = 2) were excluded. The study population also comprised a group of 12 patients in long-term remission on IFX. A functional cell-based reporter gene assay was applied to measure IFX and anti-IFX antibodies. Circulating cytokines and cytokine receptors were assessed by enzyme-linked immunosorbent assay: granulocyte-macrophage colony-stimulating factor, interferon-γ, interleukin (IL)-1α, IL-1ß, IL-1Ra, IL-6, IL-10, IL-12p70, soluble TNF receptor (sTNF-R) 1, sTNF-R2, IL-17A, and monocyte chemotactic protein 1. The IFX levels were similar between patients with IFX failure caused by nonimmune PK or PD at treatment failure (median 1.4 vs 2.4 µg/mL; P = 0.52), during treatment intensification (8.1 vs 5.6; P = 0.85), and after 12 weeks (8.8 vs 7.7; P = 0.93), congruent with nonresponders failing IFX due to predominantly TNF-α-independent signaling pathways in their disease. Cytokine and cytokine receptor levels were comparable between patients with nonimmune PK failure and PD failure at time of manifestation of IFX failure, but with higher IL-6 and sTNF-R2 levels among IFX treatment failures as compared with patients in remission (IL-6 median 3.6 vs <3.1 pg/mL; P = 0.03; sTNF-R2 3207 vs 2547 pg/mL; P = 0.01). IL-6 and sTNF-R2 were lower after 12 weeks in nonimmune PK failures than in PD failures (<3.1 vs 4.0; P = 0.02; 3209 vs 4740; P = 0.04, respectively), and were measured at levels comparable with patients in remission. Further, trends of decreased IL-6 and sTNF-R2 levels among nonimmune PK failures during IFX intensification (P < 0.05 and P = 0.12) were observed. These observations indicate that IL-6 and sTNF-R2 are of potential relevance in driving the inflammatory response in IFX refractory Crohn disease caused by TNF-α-independent disease activity.

Objective Quantification of Immune Cell Infiltrates and Epidermal Proliferation in Psoriatic Skin: A Comparison of Digital Image Analysis and Manual Counting.

Digital pathology and image analysis have developed extensively during the last couple of years. Especially the advance in whole-slide scanning, software, and computer processing makes it possible to apply these methods in tissue-based research. Today this task is dominated by tedious manual assessments by pathologists with the interobserver and intraobserver variation this includes. Automated quantitative assessment of immunohistochemical staining has the potential to objectively extract numerical measures from cell and tissue structures, and allows efficient high throughput analysis in clinical research. Published data of manual cell counts in psoriatic skin samples were in this study reevaluated using the digital image analysis (DIA) software. Whole slides immunohistochemically stained for CD3, CD4, CD8, CD45R0, and Ki-67 were scanned and quantitatively evaluated using simple threshold analysis. Regression analysis with R values in the range of 0.85 to 0.95 indicates a good correlation between the manual count of cell numbers and the staining density obtained by automated DIA. Moreover, we show that the automated image analysis is reliable over a broad range of thresholds and that it is robust to differences in staining intensities and hence useful for high throughput analysis. DIA is a viable technical approach for automated cell quantification. Its output highly correlates to the conventional manual cell counting and hence allows for increasing the throughput and reducing the analysis time significantly.

Anti-Angiogenic Drugs in the Treatment of Metastatic Renal Cell Carcinoma: Advances in Clinical Application.

The current paradigm in attempting to treat metastatic renal cell carcinoma (mRCC) is a first line treatment with a vascular endothelial growth factor (VEGF) antagonist and second and subsequent treatments with either a vascular endothelial growth factor receptor (VEGFR) or an mTOR (mammalian Target of Rapamycin) inhibitor, while conventional chemotherapeutic and hormonal treatments do not play a role in the management of mRCC. Several drugs directed against VEGF and VEGFR have been developed in recent times. Phase III data validates sunitinib, pazopanib and sorafenib as the best-supported drugs in firstline therapy. Second-line treatment possibilities include axitinib, everolimus and sorafenib. Choosing the right combination of first and second line treatments, however, is difficult, because the success of treatment depends on the precondition of the patient. Hence, biomarkers indicating the best choice of therapy in individual patients are searched and newer trials are set to determine the role of surgery and vaccination together with anti-angiogenic drugs in the treatment of mRCC. In this review, current guidelines in mRCC management are summarized and possibilities of future personalized therapies are pointed out.

Soluble L-selectin levels predict survival in sepsis.

OBJECTIVE: To evaluate serum soluble L-selectin as a prognostic factor for survival in patients with sepsis. DESIGN: A prospective study of mortality in patients with sepsis whose serum levels of sL-selectin were measured on admission to an intensive care unit (ICU) and 4 days later. Follow-up data on mortality were obtained from the Danish Central Office of Civil Registration. SETTING: A tertiary referral university hospital ICU in Copenhagen. PATIENTS: Sixty-three patients meeting the criteria for systemic inflammatory response syndrome (SIRS) with a suspected or verified infection in one or more major organs, and 14 control subjects. MEASUREMENTS AND RESULTS: On admission to the ICU the Simplified Acute Physiology Score (SAPS) II was calculated, and relevant microbial cultures were performed. Mortality was registered at various follow-up points: 7 days after admission, at discharge from hospital, and 3 and 12 months after admission. Serum sL-selectin levels were significantly lower in the patients than in the controls. Sepsis nonsurvivors had significantly lower levels than survivors. Efficiency analysis and receiver operation characteristics showed that the ideal cutoff point for sL-selectin as a test for sepsis survival was 470 ng/ml. The accumulated mortality in patients with subnormal sL-selectin levels on admission was significantly increased. No correlation was found between clinical or paraclinical markers, including SAPS II and sL-selectin, and no relationship to the microbial diagnosis was found. CONCLUSIONS: Serum sL-selectin is a predictor of survival in patients with sepsis. Those admitted with low sL-selectin (<470 ng/ml) are characterized by a high mortality within the subsequent 12-month period.

Infliximab: mechanism of action beyond TNF-alpha neutralization in inflammatory bowel disease.

Infliximab, a chimeric antibody to tumour necrosis factor-alpha (TNF-alpha), holds much promise for the treatment of patients with Crohn's disease. On the cellular level, infliximab affects survival and, as presented by Agnholt et al. in this issue of the journal, inhibits GM-CSF (granulocyte-macrophage colony-stimulating factor) production by intestinal T lymphocytes. Future studies will reveal whether the pro-apoptotic effect of infliximab is linked to its inhibition of endogenous GM-CSF expression in T cells. Treatment of Crohn's disease, a severe chronic intestinal disorder, may at times be challenging as it can be refractory to routine therapy. Among novel therapeutic strategies, agents that neutralize tumour necrosis factor-alpha (TNF-alpha) are of particular interest because of the crucial role of TNF-alpha in sustaining chronic mucosal inflammation. The exact mechanism of the anti-TNF action, apart from direct activity that neutralizes cytokines, is not fully understood. Cellular effects of TNF-alpha neutralizing treatment include an increased susceptibility to apoptosis of intestinal mucosal T cells. A novel pathway of anti-TNF-alpha interaction with T cells has been presented in the current issue of this journal. Agnholt et al. have found that in-vivo or in-vitro administration of infliximab, a chimeric antibody to TNF-alpha, resulted in a decreased production of GM-CSF (granulocyte-macrophage colony-stimulating factor) by T cells. Infliximab related down-regulation of TNF-alpha induced GM-CSF expression may be one of the mechanisms by which this drug increases the rate of apoptosis in T cells.

Ca2+ response in neutrophils after exposure to bacterial N-formyl-methionyl-leucyl-phenylalanine: delayed response in ulcerative colitis.

OBJECTIVE: In acute stages of ulcerative colitis (UC), neutrophils migrate from the circulation into inflamed colonic tissue, initiated by yet unknown stimuli. The bacterial peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP) is a component of the surface membrane of colonic bacteria such as Escherichia coli and stimulates Ca2+ influx into neutrophils, reflecting the fact that ionized calcium is an important secondary messenger for several neutrophil functions, including locomotion, phagocytosis and free oxygen radical production. Recent studies have revealed that Ca2+ dependent ICAM-1/beta 2-integrin mediated neutrophil migration is impaired in UC patients. The aim of the present work was to study the influx of Ca2+ into peripheral blood neutrophils of UC patients after exposure to FMLP and after binding of either beta 2-integrins or intercellular adhesion molecule-1 (ICAM-1). METHODS: The relative intracellular Ca2+ levels ([Ca2+]i ) were measured spectrofluorometrically in neutrophils isolated from eight UC patients and eight controls. The cells were exposed to 1 nm FMLP, 5 pm free ICAM-1, or antibodies binding ICAM-1 or the beta 2-integrins CD11a, CD11b, CD11c and CD18. RESULTS: A pronounced increase in [Ca2+]i was observed by exposure of cells to FMLP, and neutrophils from UC patients showed a consistent and significant delayed response as compared to cells from control subjects (P < 0.01). Antibody mediated cross-linking of CD18 triggered a small but detectable increase in [Ca2+]i, which did not differ between patients and controls. CONCLUSION: A delayed response to bacterial peptides appears to be a phenotypic trait for neutrophils of UC patients. A connection between FMLP stimulated Ca2+ influx and CD11/CD18 upregulation is discussed.

Inhibitors of apoptosis (IAPs) regulate intestinal immunity and inflammatory bowel disease (IBD) inflammation.

The inhibitor of apoptosis (IAP) family members, notably cIAP1, cIAP2, and XIAP, are critical and universal regulators of tumor necrosis factor (TNF) mediated survival, inflammatory, and death signaling pathways. Furthermore, IAPs mediate the signaling of nucleotide-binding oligomerization domain (NOD)1/NOD2 and other intracellular NOD-like receptors in response to bacterial pathogens. These pathways are important to the pathogenesis and treatment of inflammatory bowel disease (IBD). Inactivating mutations in the X-chromosome-linked IAP (XIAP) gene causes an immunodeficiency syndrome, X-linked lymphoproliferative disease type 2 (XLP2), in which 20% of patients develop severe intestinal inflammation. In addition, 4% of males with early-onset IBD also have inactivating mutations in XIAP. Therefore, the IAPs play a greater role in gut homeostasis, immunity and IBD development than previously suspected, and may have therapeutic potential.