Beta7 integrin deficiency suppresses B cell homing and attenuates chronic ileitis in SAMP1/YitFc mice

Sexual dimorphism in atherosclerotic plaques of aged Ldlr-/- mice

BACKGROUND

Atherosclerosis, the main underlying pathology of cardiovascular disease, is a chronic inflammatory disease characterized by lipid accumulation and immune cell responses in the vascular wall, resulting in plaque formation. It is well-known that atherosclerosis prevalence and manifestation vary by sex. However, sexual dimorphism in the immune landscape of atherosclerotic plaques has up to date not been studied at high-resolution. In this study, we investigated sex-specific differences in atherosclerosis development and the immunological landscape of aortas at single-cell level in aged Ldlr-/- mice.

METHODS

We compared plaque morphology between aged male and female chow diet-fed Ldlr-/- mice (22 months old) with histological analysis. Using single-cell RNA-sequencing and flow cytometry on CD45+ immune cells from aortas of aged Ldlr-/- mice, we explored the immune landscape in the atherosclerotic environment in males and females.

RESULTS

We show that plaque volume is comparable in aged male and female mice, and that plaques in aged female mice contain more collagen and cholesterol crystals, but less necrotic core and macrophage content compared to males. We reveal increased immune cell infiltration in female aortas and found that expression of pro-atherogenic markers and inflammatory signaling pathways was enriched in plaque immune cells of female mice. Particularly, female aortas show enhanced activation of B cells (Egr1, Cd83, Cd180), including age-associated B cells, in addition to an increased M1/M2 macrophage ratio, where Il1b+ M1-like macrophages display a more pro-inflammatory phenotype (Nlrp3, Cxcl2, Mmp9) compared to males. In contrast, increased numbers of age-associated Gzmk+CD8+ T cells, dendritic cells, and Trem2+ macrophages were observed in male aortas.

CONCLUSIONS

Altogether, our findings highlight that sex is a variable that contributes to immunological differences in the atherosclerotic plaque environment in mice and provide valuable insights for further preclinical studies into the impact of sex on the pathophysiology of atherosclerosis.

Targeting integrin pathways: mechanisms and advances in therapy

Integrins are considered the main cell-adhesion transmembrane receptors that play multifaceted roles as extracellular matrix (ECM)-cytoskeletal linkers and transducers in biochemical and mechanical signals between cells and their environment in a wide range of states in health and diseases. Integrin functions are dependable on a delicate balance between active and inactive status via multiple mechanisms, including protein-protein interactions, conformational changes, and trafficking. Due to their exposure on the cell surface and sensitivity to the molecular blockade, integrins have been investigated as pharmacological targets for nearly 40 years, but given the complexity of integrins and sometimes opposite characteristics, targeting integrin therapeutics has been a challenge. To date, only seven drugs targeting integrins have been successfully marketed, including abciximab, eptifibatide, tirofiban, natalizumab, vedolizumab, lifitegrast, and carotegrast. Currently, there are approximately 90 kinds of integrin-based therapeutic drugs or imaging agents in clinical studies, including small molecules, antibodies, synthetic mimic peptides, antibody-drug conjugates (ADCs), chimeric antigen receptor (CAR) T-cell therapy, imaging agents, etc. A serious lesson from past integrin drug discovery and research efforts is that successes rely on both a deep understanding of integrin-regulatory mechanisms and unmet clinical needs. Herein, we provide a systematic and complete review of all integrin family members and integrin-mediated downstream signal transduction to highlight ongoing efforts to develop new therapies/diagnoses from bench to clinic. In addition, we further discuss the trend of drug development, how to improve the success rate of clinical trials targeting integrin therapies, and the key points for clinical research, basic research, and translational research.

Harnessing murine models of Crohn's disease ileitis to advance concepts of pathophysiology and treatment

Crohn's disease (CD) and ulcerative colitis (UC) are both characterized by chronic inflammation and severe dysfunction of the gastrointestinal tract. These two forms of inflammatory bowel disease (IBD) represent distinct clinical disorders with diverse driving mechanisms; however, this divergence is not reflected in currently approved therapeutics that commonly target general proinflammatory pathways. A compelling need therefore remains to understand factors that differentiate the topology and the distinct clinical manifestations of CD versus UC, in order to develop more effective and specialized therapies. Animal models provide valuable platforms for studying IBD heterogeneity and deciphering disease-specific mechanisms. Both the established and the newly developed ileitis mouse models are characterized by various disease initiating mechanisms and diverse phenotypic outcomes that reflect the complexity of human CD-ileitis. Microbial dysbiosis, destruction of epithelial barrier integrity, immune cell deregulation, as well as the recently described genome instability and stromal cell activation have all been proposed as the triggering factors for the development of ileitis-associated pathology. In this review, we aim to critically evaluate the mechanistic underpinnings of murine models of CD-ileitis, discuss their phenotypic similarities to human disease, and envisage their further exploitation for the development of novel targeted and personalized therapeutics.

Inhibition of mPGES-1 attenuates efficient resolution of acute inflammation by enhancing CX3CL1 expression

Despite the progress to understand inflammatory reactions, mechanisms causing their resolution remain poorly understood. Prostanoids, especially prostaglandin E2 (PGE2), are well-characterized mediators of inflammation. PGE2 is produced in an inducible manner in macrophages (Mϕ) by microsomal PGE2-synthase-1 (mPGES-1), with the notion that it also conveys pro-resolving properties. We aimed to characterize the role of mPGES-1 during resolution of acute, zymosan-induced peritonitis. Experimentally, we applied the mPGES-1 inhibitor compound III (CIII) once the inflammatory response was established and confirmed its potent PGE2-blocking efficacy. mPGES-1 inhibition resulted in an incomplete removal of neutrophils and a concomitant increase in monocytes and Mϕ during the resolution process. The mRNA-seq analysis identified enhanced C-X3-C motif receptor 1 (CX3CR1) expression in resident and infiltrating Mϕ upon mPGES-1 inhibition. Besides elevated Cx3cr1 expression, its ligand CX3CL1 was enriched in the peritoneal lavage of the mice, produced by epithelial cells upon mPGES-1 inhibition. CX3CL1 not only increased adhesion and survival of Mϕ but its neutralization also completely reversed elevated inflammatory cell numbers, thereby normalizing the cellular, peritoneal composition during resolution. Our data suggest that mPGES-1-derived PGE2 contributes to the resolution of inflammation by preventing CX3CL1-mediated retention of activated myeloid cells at sites of injury.

Opportunities to Target T Cell Trafficking in Pediatric Inflammatory Bowel Disease

T cell subsets are considered central orchestrators of inflammation and homeostasis in the intestine and are established targets for the treatment of inflammatory bowel disease. While approaches aimed at the neutralization of T cell effector cytokines have provided significant benefits for pediatric and adult patients, more recent strategies aimed at inhibiting the infiltration of pathogenic T cell subsets have also emerged. In this review, we describe current knowledge surrounding the function of T cell subsets in pediatric inflammatory bowel disease and outline approaches aimed at targeting T cell trafficking to the intestine which may represent a new treatment option for pediatric inflammatory bowel disease.

A mutation that blocks integrin α4β7 activation prevents adaptive immune-mediated colitis without increasing susceptibility to innate colitis

Background

β₇ integrins are responsible for the efficient recruitment of lymphocytes from the blood and their retention in gut-associated lymphoid tissues. Integrin α₄β₇ binds MAdCAM-1, mediating rolling adhesion of lymphocytes on blood vessel walls when inactive and firm adhesion when activated, thereby controlling two critical steps of lymphocyte homing to the gut. By contrast, integrin α_Eβ₇ mediates the adhesion of lymphocytes to gut epithelial cells by interacting with E-cadherin. Integrin β₇ blocking antibodies have shown efficacy in clinical management of inflammatory bowel disease (IBD); however, fully blocking β₇ function leads to the depletion of colonic regulatory T (Treg) cells and exacerbates dextran sulfate sodium (DSS)-induced colitis by evoking aberrant innate immunity, implying its potential adverse effect for IBD management. Thus, a better therapeutic strategy targeting integrin β₇ is required to avoid this adverse effect.

Results

Herein, we inhibited integrin α₄β₇ activation in vivo by creating mice that carry in their integrin β₇ gene a mutation (F185A) which from structural studies is known to lock α₄β₇ in its resting state. Lymphocytes from β₇-F185A knock-in (KI) mice expressed α₄β₇ integrins that could not be activated by chemokines and showed significantly impaired homing to the gut. The β₇-F185A mutation did not inhibit α_Eβ₇ activation, but led to the depletion of α_Eβ₇⁺ lymphocytes in the spleen and a significantly reduced population of α_Eβ₇⁺ lymphocytes in the gut of KI mice. β₇-F185A KI mice were resistant to T cell transfer-induced chronic colitis, but did not show an increased susceptibility to DSS-induced innate colitis, the adverse effect of fully blocking β₇ function.

Conclusions

Our findings demonstrate that specific inhibition of integrin α₄β₇ activation is a potentially better strategy than fully blocking α₄β₇ function for IBD treatment.

β7 Integrin Inhibition Can Increase Intestinal Inflammation by Impairing Homing of CD25hiFoxP3+ Regulatory T Cells

BACKGROUND & AIMS

Integrin α4β7 mediates lymphocyte trafficking to the gut and gut-associated lymphoid tissues, a process critical for recruitment of effector lymphocytes from the circulation to the gut mucosa in inflammatory bowel disease (IBD) and murine models of intestinal inflammation. Antibody blockade of β7 integrins generally is efficacious in IBD; however, some patients fail to respond, and a few patients can experience exacerbations. This study examined the effects of loss of β7 integrin function in murine models of IBD.

METHODS

In a mouse IBD model caused by lack of interleukin 10, a cytokine important in CD25hiFoxP3+ regulatory T cell (Treg) function, genetic deletion of β7 integrin or antibody blockade of α4β7-mucosal addressin cell adhesion molecule-1 interaction paradoxically exacerbated colitis.

RESULTS

Loss of β7 impaired the capacity of Tregs homing to the gut and therefore suppress intestinal inflammation in an adoptive T-cell transfer model; however, the intrinsic suppressive function of β7-deficient Tregs remained intact, indicating that the β7 deficiency selectively impacts gut homing. Deletion of β7 integrin did not worsen colitis in an acute dextran sodium sulfate model in which Treg number and function were normal.

CONCLUSIONS

In Integrin subunit beta (Itgb)7-/-Il10-/- mice, loss of β7-dependent Treg homing to gut-associated lymphoid tissues combined with loss of intrinsic Treg function exacerbated intestinal inflammation. These results suggest that IBD patients with reduced CD25hiFoxP3+ Treg numbers or function or lack of interleukin 10 could be at risk for failure of α4β7 blocking therapy.

The Histone Demethylase LSD1 Regulates B Cell Proliferation and Plasmablast Differentiation

B cells undergo epigenetic remodeling as they differentiate into Ab-secreting cells (ASC). LSD1 is a histone demethylase known to decommission active enhancers and cooperate with the ASC master regulatory transcription factor Blimp-1. The contribution of LSD1 to ASC formation is poorly understood. In this study, we show that LSD1 is necessary for proliferation and differentiation of mouse naive B cells (nB) into plasmablasts (PB). Following LPS inoculation, LSD1-deficient hosts exhibited a 2-fold reduction of splenic PB and serum IgM. LSD1-deficient PB exhibited derepression and superinduction of genes involved in immune system processes; a subset of these being direct Blimp-1 target-repressed genes. Cell cycle genes were globally downregulated without LSD1, which corresponded to a decrease in the proliferative capacity of LSD1-deficient activated B cells. PB lacking LSD1 displayed increased histone H3 lysine 4 monomethylation and chromatin accessibility at nB active enhancers and the binding sites of transcription factors Blimp-1, PU.1, and IRF4 that mapped to LSD1-repressed genes. Together, these data show that LSD1 is required for normal in vivo PB formation, distinguish LSD1 as a transcriptional rheostat and epigenetic modifier of B cell differentiation, and identify LSD1 as a factor responsible for decommissioning nB active enhancers.

Transcriptome analysis of ovine granulosa cells reveals differences between small antral follicles collected during the follicular and luteal phases

Ovarian follicular growth occurs in both the follicular and luteal phases of the estrous cycle but in very different endocrine contexts. In both phases, many small antral follicles with similar morphologic and histologic characteristics are present within the ovaries as a reserve for the terminal folliculogenesis. However, there are several gaps in our molecular knowledge of the gene expression profiles of small antral follicles in the follicular and luteal phases. The aim of the present study was to use RNA sequencing to compare and analyze the global transcriptional profile of ovine granulosa cells collected from small antral follicles (1-3 mm) either during the follicular or the luteal phase of the estrous cycle, with the hypothesis that they should be differential. We identified 663 genes whose mRNA was differentially expressed or accumulated in the granulosa cell layer of small antral follicles in the two phases. A comprehensive interpretation of these data was performed through integrative analyses (Gene Ontology, Ingenuity Pathway Analysis) and the exploitation of already available transcriptomic data on follicular growth and atresia. In particular, we observed that the contrasted endocrine context between follicular and luteal phases may have an impact on estradiol, follicle-stimulating hormone (FSH), and on the activin/inhibin signaling pathways. Furthermore, we reveal the possible initiation of early follicular atresia in small antral follicles during the follicular phase in interaction with the presence of immune cells. This study provides new insights into the gene expression profile in ovine granulosa cells, and we suggest that these molecular changes may have an implication at the time of follicle selection.

Uncovering Pathogenic Mechanisms of Inflammatory Bowel Disease Using Mouse Models of Crohn's Disease-Like Ileitis: What is the Right Model?

Crohn's disease and ulcerative colitis, together known as inflammatory bowel disease, are debilitating chronic disorders of unknown cause and cure. Our evolving understanding of these pathologies is enhanced greatly by the use of animal models of intestinal inflammation that allow in vivo mechanistic studies, preclinical evaluation of new therapies, and investigation into the causative factors that underlie disease pathogenesis. Several animal models, most commonly generated in mice, exist for the study of colitis. The appropriateness of their use often can be determined by their mode of generation (ie, chemical induction, T-cell transfer, targeted genetic manipulation, spontaneously occurring, and so forth), the type of investigation (mechanistic studies, pathogenic experiments, preclinical evaluations, and so forth), and the type of inflammation that occurs in the model (acute vs chronic colitis, tissue injury/repair, and so forth). Although most murine models of inflammatory bowel disease develop inflammation in the colon, Crohn's disease most commonly occurs in the terminal ileum, where a very limited number of mouse models manifest disease. This review discusses appropriate experimental applications for different mouse models of colitis, and highlights the particular utility of 2 highly relevant models of Crohn's-like ileitis-the spontaneous SAMP1/YitFc inbred mouse strain and the genetically engineered Tnf^{ΔAU-rich element/+} mouse model of tumor necrosis factor overexpression, both of which bear strong resemblance to the human condition. Similar to patients with Crohn's disease, SAMP1/YitFc ileitis develops spontaneously, without chemical, genetic, or immunologic manipulation, making this model particularly relevant for studies aimed at identifying the primary defect underlying the occurrence of Crohn's ileitis, as well as preclinical testing of novel treatment modalities.

Regulatory T-cell depletion in the gut caused by integrin β7 deficiency exacerbates DSS colitis by evoking aberrant innate immunity

Integrin α4β7 controls lymphocyte trafficking into the gut and has essential roles in inflammatory bowel disease (IBD). The α4β7-blocking antibody vedolizumab is approved for IBD treatment; however, high dose of vedolizumab aggravates colitis in a small percentage of patients. Herein, we show that integrin β7 deficiency results in colonic regulatory T (Treg) cell depletion and exacerbates dextran sulfate sodium (DSS) colitis by evoking aberrant innate immunity. In DSS-treated β7-deficient mice, the loss of colonic Treg cells induces excessive macrophage infiltration in the colon via upregulation of colonic epithelial intercellular adhesion molecule 1 and increases proinflammatory cytokine expression, thereby exacerbating DSS-induced colitis. Moreover, reconstitution of the colonic Treg cell population in β7-deficient mice suppresses aberrant innate immune response in the colon and attenuates DSS colitis. Thus, integrin α4β7 is essential for suppression of DSS colitis as it regulates the colonic Treg cell population and innate immunity.

Dysregulated intrahepatic CD4+ T-cell activation drives liver inflammation in ileitis-prone SAMP1/YitFc mice

BACKGROUND AND AIMS

Liver inflammation is a common extraintestinal manifestation of inflammatory bowel disease (IBD); however, whether liver involvement is a consequence of a primary intestinal defect or results from alternative pathogenic processes remains unclear. Therefore, we sought to determine the potential pathogenic mechanism(s) of concomitant liver inflammation in an established murine model of IBD.

METHODS

Liver inflammation and immune cell subsets were characterized in ileitis-prone SAMP1/YitFc (SAMP) and AKR/J (AKR) control mice, lymphocyte-depleted SAMP (SAMPxRag-1^-/-), and immunodeficient SCID recipient mice receiving SAMP or AKR donor CD4⁺ T-cells. Proliferation and suppressive capacity of CD4⁺ T-effector (Teff) and T-regulatory (Treg) cells from gut-associated lymphoid tissue (GALT) and livers of SAMP and AKR mice were measured.

RESULTS

Surprisingly, prominent inflammation was detected in 4-wk-old SAMP livers, prior to histologic evidence of ileitis, while both disease phenotypes were absent in age-matched AKRs. SAMP liver disease was characterized by abundant infiltration of lymphocytes, required for hepatic inflammation to occur, a Th1-skewed environment, and phenotypically-activated CD4⁺ T-cells. SAMP intrahepatic CD4⁺ T-cells also had the ability to induce liver and ileal inflammation when adoptively transferred into SCID recipients, whereas GALT-derived CD4⁺ T-cells produced milder ileitis, but not liver inflammation. Interestingly, SAMP intrahepatic CD4⁺ Teff cells showed increased proliferation compared to both SAMP GALT- and AKR liver-derived CD4⁺ Teff cells, while SAMP intrahepatic Tregs were decreased among CD4⁺ T-cells and impaired in in vitro suppressive function compared to AKR.

CONCLUSIONS

Activated intrahepatic CD4⁺ T-cells induce liver inflammation and contribute to experimental ileitis via locally-impaired hepatic immunosuppressive function.

Leukocyte integrins: role in leukocyte recruitment and as therapeutic targets in inflammatory disease

Infection or sterile inflammation triggers site-specific attraction of leukocytes. Leukocyte recruitment is a process comprising several steps orchestrated by adhesion molecules, chemokines, cytokines and endogenous regulatory molecules. Distinct adhesive interactions between endothelial cells and leukocytes and signaling mechanisms contribute to the temporal and spatial fine-tuning of the leukocyte adhesion cascade. Central players in the leukocyte adhesion cascade include the leukocyte adhesion receptors of the β2-integrin family, such as the αLβ2 and αMβ2 integrins, or of the β1-integrin family, such as the α4β1-integrin. Given the central involvement of leukocyte recruitment in different inflammatory and autoimmune diseases, the leukocyte adhesion cascade in general, and leukocyte integrins in particular, represent key therapeutic targets. In this context, the present review focuses on the role of leukocyte integrins in the leukocyte adhesion cascade. Experimental evidence that has implicated leukocyte integrins as targets in animal models of inflammatory disorders, such as experimental autoimmune encephalomyelitis, psoriasis, inflammatory bone loss and inflammatory bowel disease as well as preclinical and clinical therapeutic applications of antibodies that target leukocyte integrins in various inflammatory disorders are presented. Finally, we review recent findings on endogenous inhibitors that modify leukocyte integrin function, which could emerge as promising therapeutic targets.

In vivo inhibition of RIPK2 kinase alleviates inflammatory disease

The RIPK2 kinase transduces signaling downstream of the intracellular peptidoglycan sensors NOD1 and NOD2 to promote a productive inflammatory response. However, excessive NOD2 signaling has been associated with numerous diseases, including inflammatory bowel disease (IBD), sarcoidosis and inflammatory arthritis, making pharmacologic inhibition of RIPK2 an appealing strategy. In this work, we report the generation, identification, and evaluation of novel RIPK2 specific inhibitors. These compounds potently inhibit the RIPK2 tyrosine kinase activity in in vitro biochemical assays and cellular assays, as well as effectively reduce RIPK2-mediated effects in an in vivo peritonitis model. In conjunction with the development of these inhibitors, we have also defined a panel of genes whose expression is regulated by RIPK2 kinase activity. Such RIPK2 activation markers may serve as a useful tool for predicting settings likely to benefit from RIPK2 inhibition. Using these markers and the FDA-approved RIPK2 inhibitor Gefitinib, we show that pharmacologic RIPK2 inhibition drastically improves disease in a spontaneous model of Crohn Disease-like ileitis. Furthermore, using novel RIPK2-specific inhibitors, we show that cellular recruitment is inhibited in an in vivo peritonitis model. Altogether, the data presented in this work provides a strong rationale for further development and optimization of RIPK2-targeted pharmaceuticals and diagnostics.

The value of experimental models of colitis in predicting efficacy of biological therapies for inflammatory bowel diseases

During the last decade, biological therapies have an increasing share in the modern therapeutics of various diseases including inflammatory bowel diseases (IBD). Animal models of IBD have often been used to identify the targets of biological therapies, to test their relevance to disease pathogenesis, to assess their therapeutic efficacy in vivo, and to check for drug toxicity. In the field of inflammatory diseases the majority of biologics under development have failed to reach the clinic. This review examines the ability of preclinical data from animal models of IBD to predict success or failure of biologics in human IBD. Specifically, it describes the murine models of IBD, the mechanism of disease induction, the phenotype of the disease, its relevance to human IBD, and the specific immunological features of disease pathogenesis in each model and mainly compares the results of the phase II and III trials of biologics in IBD with preclinical data obtained from studies in animal models. Finally, it examines the possible reasons for low success in translation from bench to bedside and offers some suggestions to improve translation rates.

Roles of T cell-associated L-selectin and β7 integrins during induction and regulation of chronic colitis

BACKGROUND

L-selectin (CD62L) and β(7) integrins are important for trafficking of naive T cells under steady-state conditions. The objectives of this study were to dissect the requirements for T cell-associated CD62L and β(7) integrins during initiation, progression, and regulation of chronic colitis.

METHODS

Using the T-cell transfer model, we compared colitogenic potential between T cells lacking one or both of these molecules with wild-type T cells. To assess trafficking of cells to the secondary lymphoid tissue and the gut, we performed co-homing experiments.

RESULTS

Adoptive transfer of wild-type, CD62L(-/-) or β(7)(-/-) single-deficient T cells induced moderate to severe disease with slightly different kinetics. However, transfer of CD62L(-/-) β(7)(-/-) double-deficient (DKO) T cells produced significantly attenuated gut inflammation, which correlated with fewer T cells and reduced levels of proinflammatory cytokines in the colon lamina propria. Our subsequent experiments established that lack of colitogenic potential of these cells was due to inability of DKO T cells to home to the secondary lymphoid tissue. Furthermore, homing of in vitro-generated effector DKO T cells to the inflamed intestine was significantly impaired. Lastly, DKO regulatory T cells were ineffective at suppressing colitis induced by wild-type T cells.

CONCLUSIONS

We established that T cells can use either CD62L(-/-) or β(7)(-/-) integrins to induce chronic colitis, but lack of both abrogates their colitogenic potential. Effector T cells critically rely on β(7) integrin during their recruitment to the inflamed intestinal mucosa. Finally, regulation of intestinal inflammation by regulatory T cells requires one or both of these adhesion molecules.

Spontaneous autoimmune gastritis and hypochlorhydria are manifest in the ileitis-prone SAMP1/YitFcs mice

SAMP1/YitFcs mice serve as a model of Crohn's disease, and we have used them to assess gastritis. Gastritis was compared in SAMP1/YitFcs, AKR, and C57BL/6 mice by histology, immunohistochemistry, and flow cytometry. Gastric acid secretion was measured in ligated stomachs, while anti-parietal cell antibodies were assayed by immunofluorescence and enzyme-linked immunosorbent spot assay. SAMP1/YitFcs mice display a corpus-dominant, chronic gastritis with multifocal aggregates of mononuclear cells consisting of T and B lymphocytes. Relatively few aggregates were observed elsewhere in the stomach. The infiltrates in the oxyntic mucosa were associated with the loss of parietal cell mass. AKR mice, the founder strain of the SAMP1/YitFcs, also have gastritis, although they do not develop ileitis. Genetic studies using SAMP1/YitFcs-C57BL/6 congenic mice showed that the genetic regions regulating ileitis had comparable effects on gastritis. The majority of the cells in the aggregates expressed the T cell marker CD3 or the B cell marker B220. Adoptive transfer of SAMP1/YitFcs CD4(+) T helper cells, with or without B cells, into immunodeficient recipients induced a pangastritis and duodenitis. SAMP1/YitFcs and AKR mice manifest hypochlorhydria and anti-parietal cell antibodies. These data suggest that common genetic factors controlling gastroenteric disease in SAMP1/YitFcs mice regulate distinct pathogenic mechanisms causing inflammation in separate sites within the digestive tract.

SAMP1/YitFc mouse strain: a spontaneous model of Crohn's disease-like ileitis

The SAMP1/YitFc mouse strain represents a model of Crohn's disease (CD)-like ileitis that is ideal for investigating the pathogenesis of chronic intestinal inflammation. Different from the vast majority of animal models of colitis, the ileal-specific phenotype characteristic of SAMP1/YitFc mice occurs spontaneously, without genetic, chemical, or immunological manipulation. In addition, SAMP1/YitFc mice possess remarkable similarities to the human condition with regard to disease location, histologic features, incidence of extraintestinal manifestations, and response to conventional therapies. SAMP1/YitFc mice also display a well-defined time course of a predisease state and phases of acute and chronic ileitis. As such, the SAMP1/YitFc model is particularly suitable for elucidating pathways that precede the clinical phenotype that may lead to preventive, and therefore more efficacious, intervention with the natural course of disease, or alternatively, for the development of therapeutic strategies directed against chronic, established ileitis. In this review we summarize important contributions made by our group and others that uncover potential mechanisms in the pathogenesis of CD using this unique murine model of chronic intestinal inflammation.

Pathogenesis of gastritis in ileitis-prone SAMP1/Yit mice

Inflammatory bowel disease is a chronic inflammatory disease of the gut which manifests as ulcerative colitis or Crohn's disease. One of the most studied animal models of spontaneous Crohn's disease is the senescence-accelerated mouse (SAMP1/Yit strain) model. In SAMP1/Yit mice, although many immunological responses are perturbed, some evidence suggests that the primary defect lies in the epithelial cell barrier. In the process of studying epithelial permeability, we observed that the stomach in SAMP1/Yit mice also had increased permeability. Upon further examination, these mice were shown to have marked, chronic gastritis with focal to diffuse aggregates of mononuclear cells of mixed lineages. These aggregates were located predominantly in the oxyntic mucosa, with occasional lesions in the forestomach but with relatively fewer cellular infiltrates in the antral mucosa. Real-time RT PCR showed an increase in several helper T cell (Th cell)-derived pro-inflammatory cytokines in the gastric mucosa of SAMP1/Yit mice. However, many of the cells in the aggregates of SAMP1/Yit mice were B cells. SAMP1/Yit B cells exacerbate ileitis when co-transferred into immunodeficient recipients. The gastritis also reflects a contribution by B cells. As SAMP1/Yit mice were derived from AKR mice, we examined AKR mice and determined that they too have an increased occurrence of gastritis, although they do not develop ileitis. B cells contributed to the gastric inflammation in these mice also. Thus, SAMP1/Yit mice display gastritis as well as ileitis, and B cells appear to play a role in the pathogenesis of inflammation at both sites. This review will discuss some of the mechanisms that may account for these different manifestations of gastrointestinal disease.

Blocking lymphocyte localization to the gastrointestinal mucosa as a therapeutic strategy for inflammatory bowel diseases

Lymphocyte migration (homing) to specific tissues has an important role during protective and pathological immune responses, including inflammatory bowel diseases. Lymphocytes use integrin α4β7 and the chemokine receptor CCR9 to localize to the gastrointestinal mucosa; their respective ligands, mucosal addressin cell adhesion molecule-1 and CCL25, are displayed on endothelial cells in intestinal postcapillary venules. Although gastrointestinal-homing receptors are required for lymphocyte migration to the intestine in the noninflamed steady state, their role during inflammation is a matter of debate. Reagents designed to block interactions between these receptors and their ligands have had variable degrees of success in animal models of inflammatory bowel diseases and patients. We discuss the mechanisms involved in lymphocyte localization to the intestinal mucosa and how they can be applied to therapy for inflammatory bowel diseases.

Whole blood transcriptional profiling in ankylosing spondylitis identifies novel candidate genes that might contribute to the inflammatory and tissue-destructive disease aspects

INTRODUCTION

A number of genetic-association studies have identified genes contributing to ankylosing spondylitis (AS) susceptibility but such approaches provide little information as to the gene activity changes occurring during the disease process. Transcriptional profiling generates a 'snapshot' of the sampled cells' activity and thus can provide insights into the molecular processes driving the disease process. We undertook a whole-genome microarray approach to identify candidate genes associated with AS and validated these gene-expression changes in a larger sample cohort.

METHODS

A total of 18 active AS patients, classified according to the New York criteria, and 18 gender- and age-matched controls were profiled using Illumina HT-12 whole-genome expression BeadChips which carry cDNAs for 48,000 genes and transcripts. Class comparison analysis identified a number of differentially expressed candidate genes. These candidate genes were then validated in a larger cohort using qPCR-based TaqMan low density arrays (TLDAs).

RESULTS

A total of 239 probes corresponding to 221 genes were identified as being significantly different between patients and controls with a P-value <0.0005 (80% confidence level of false discovery rate). Forty-seven genes were then selected for validation studies, using the TLDAs. Thirteen of these genes were validated in the second patient cohort with 12 downregulated 1.3- to 2-fold and only 1 upregulated (1.6-fold). Among a number of identified genes with well-documented inflammatory roles we also validated genes that might be of great interest to the understanding of AS progression such as SPOCK2 (osteonectin) and EP300, which modulate cartilage and bone metabolism.

CONCLUSIONS

We have validated a gene expression signature for AS from whole blood and identified strong candidate genes that may play roles in both the inflammatory and joint destruction aspects of the disease.