New pathogenic paradigms in inflammatory bowel disease

Inflammatory bowel disease: Pathogenesis

Inflammatory bowel disease (IBD), including Crohn’s disease and ulcerative colitis, is characterized by chronic relapsing intestinal inflammation. It has been a worldwide health-care problem with a continually increasing incidence. It is thought that IBD results from an aberrant and continuing immune response to the microbes in the gut, catalyzed by the genetic susceptibility of the individual. Although the etiology of IBD remains largely unknown, it involves a complex interaction between the genetic, environmental or microbial factors and the immune responses. Of the four components of IBD pathogenesis, most rapid progress has been made in the genetic study of gut inflammation. The latest internationally collaborative studies have ascertained 163 susceptibility gene loci for IBD. The genes implicated in childhood-onset and adult-onset IBD overlap, suggesting similar genetic predispositions. However, the fact that genetic factors account for only a portion of overall disease variance indicates that microbial and environmental factors may interact with genetic elements in the pathogenesis of IBD. Meanwhile, the adaptive immune response has been classically considered to play a major role in the pathogenesis of IBD, as new studies in immunology and genetics have clarified that the innate immune response maintains the same importance in inducing gut inflammation. Recent progress in understanding IBD pathogenesis sheds lights on relevant disease mechanisms, including the innate and adaptive immunity, and the interactions between genetic factors and microbial and environmental cues. In this review, we provide an update on the major advances that have occurred in above areas.

Faecalibacterium prausnitzii upregulates regulatory T cells and anti-inflammatory cytokines in treating TNBS-induced colitis

BACKGROUND AND AIMS

Faecalibacterium prausnitzii (F. prausnitzii) is a common anaerobic bacteria colonized in the human gut and inflammatory bowel disease (IBD) patients are usually lack of F. prausnitzii. The aims of this study were to evaluate the anti-inflammatory and immunomodulatory capacity of F. prausnitzii by comparing it with Bifidobacterium longum (B. longum) in both cellular and animal experiments.

METHODS

Human peripheral blood mononuclear cells (PBMCs) and 2, 4, 6-trinitrobenzenesulphonic acid (TNBS)-induced colitis rat models were treated with F. prausnitzii, B. longum, F. prausnitzii supernatant or F. prausnitzii medium, respectively. Interleukin (IL)-10, TGF-β1 and IL-12p70 in human PBMCs culture supernatant and rat blood serum were detected. The frequency of CD25(+)Foxp3(+)Treg in human PBMCs, rat PBMCs and rat splenocytes were investigated. Besides, the T-bet, GATA-3, ROR-γt and Foxp3 mRNA in human PBMCs, histopathologic characteristics of the intestinal mucosal and weight loss in the rat models were examined.

RESULTS

F. prausnitzii, B. longum and F. prausnitzii supernatant clearly facilitated the induction of IL-10 and TGF-β1, while induced relatively mild production of IL-12p70 in both cellular and animal models. The F. prausnitzii, B. longum and supernatant differed in their capacity to induce T-bet, GATA-3 and ROR-γt mRNA expression in human PBMCs (both bacterial strains inhibited the expression of ROR-γt while supernatant inhibited the T-bet and GATA-3). However, all of them induced the Foxp3 and Treg production and ameliorated the TNBS-induced colitis. In addition, F. prausnitzii supernatant exhibited the supreme anti-inflammatory capacity.

CONCLUSIONS

F. prausnitzii and its unidentified metabolites in the supernatant are promising candidates in treating IBD, and further research remains necessary to elucidate the safety, efficacy, optimum and mechanism of this bacterium in the clinical practice.

The role of transforming growth factor (TGF)-β in modulating the immune response and fibrogenesis in the gut

Transforming growth factor (TGF)-β, a pleiotropic cytokine released by both immune and non-immune cells in the gut, exerts an important tolerogenic action by promoting regulatory T cell differentiation. TGF-β also enhances enterocyte migration and regulates extracellular matrix turnover, thereby playing a crucial role in tissue remodeling in the gut. In this review we describe the mechanisms by which abnormal TGF-β signaling impairs intestinal immune tolerance and tissue repair, thus predisposing to the onset of immune-mediated bowel disorders, such as inflammatory bowel disease and celiac disease. Additionally, we will discuss potential therapeutic strategies aiming at restoring physiologic TGF-β signaling in chronic intestinal diseases.

The challenges of stratifying patients for trials in inflammatory bowel disease

Immunotherapy with biological agents or small molecules is revolutionising the treatment of chronic inflammatory disease in humans; however, a significant proportion of patients fail to respond or lose responsiveness. This is particularly evident in inflammatory bowel disease (IBD), a group of chronic, immune-mediated disorders of the gastrointestinal tract. Different responsiveness to treatment in IBD can be explained by substantial disease heterogeneity, which is being increasingly recognised by genetic and immunological studies. The current enthusiasm for stratified medicine suggests that it may become possible to identify clinical, immunological, biochemical or genetic biomarkers to target immunotherapy to patients more likely to respond. Here, we identify and highlight the opportunities and the challenges of this strategy in the context of IBD.

Anti-tumour necrosis factor therapy enhances mucosal healing through down-regulation of interleukin-21 expression and T helper type 17 cell infiltration in Crohn's disease

Anti-tumour necrosis factor (TNF) monoclonal antibody (mAb) (infliximab, IFX) has been shown to be highly effective in the management of Crohn's disease (CD). Herein we investigated the potential role of IFX in inducing clinical remission and regulating interleukin (IL)-21 expression and T helper type 17 (Th17) cell infiltration in the intestinal mucosa of CD patients. Twenty-six CD patients were treated with IFX at weeks 0, 2 and 6. Clinical response, mucosal healing, serum C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) were evaluated at week 10 after IFX administration. Expression of IL-21, IL-17A and retinoic acid-related orphan receptor C (RORC) in intestinal mucosa were analysed by quantitative real-time polymerase chain reaction (PCR) and immunohistochemistry. Peripheral blood and lamina propria CD4(+) T cells were stimulated with anti-CD3 and anti-CD28 mAbs in the presence of IFX. Cytokine profiles and RORC were determined with enzyme-linked immunosorbent assay (ELISA) and real-time PCR. IL-21 and Th17 cells were found to be expressed highly in inflamed mucosa of active CD patients compared with healthy controls. Ten weeks after IFX infusion, CD activity index, ESR, CRP and intestinal mucosal healing were improved markedly in CD patients, and IL-21 expression and Th17 cell infiltration were decreased significantly compared with those before IFX therapy. In-vitro study demonstrated that IFX treatment could suppress IL-21, IL-17A and RORC expression in cultured CD biopsies. Moreover, IFX was also observed to down-regulate markedly IL-17A, IL-21 and RORC expression by CD CD4(+) T cells. IFX is highly effective in inducing clinical remission and promoting intestinal mucosal healing in CD patients through down-regulation of IL-21 expression and Th17 cell infiltration in intestinal mucosa.

Innate and adaptive immunity in inflammatory bowel disease

Inflammatory bowel disease (IBD) includes Crohn's disease (CD) and ulcerative colitis (UC). The exact cause of IBD remains unknown. Available evidence suggests that an abnormal immune response against the microorganisms of the intestinal flora is responsible for the disease in genetically susceptible individuals. The adaptive immune response has classically been considered to play a major role in the pathogenesis of IBD. However, recent advances in immunology and genetics have clarified that the innate immune response is equally as important in inducing gut inflammation in these patients. In particular, an altered epithelial barrier function contributes to intestinal inflammation in patients with UC, while aberrant innate immune responses, such as antimicrobial peptide production, innate microbial sensing and autophagy are particularly associated to CD pathogenesis. On the other hand, besides T helper cell type (Th)1 and Th2 immune responses, other subsets of T cells, namely Th17 and regulatory T (Treg) cells, are likely to play a role in IBD. However, given the complexity and probably the redundancy of pathways leading to IBD lesions, and the fact that Th17 cells may also have protective functions, neutralization of IL-17A failed to induce any improvement in CD. Studying the interactions between various constituents of the innate and adaptive immune systems will certainly open new horizons in the knowledge about the immunologic mechanisms implicated in gut inflammation.

Whole genome gene expression meta-analysis of inflammatory bowel disease colon mucosa demonstrates lack of major differences between Crohn's disease and ulcerative colitis

Background

In inflammatory bowel disease (IBD), genetic susceptibility together with environmental factors disturbs gut homeostasis producing chronic inflammation. The two main IBD subtypes are Ulcerative colitis (UC) and Crohn’s disease (CD). We present the to-date largest microarray gene expression study on IBD encompassing both inflamed and un-inflamed colonic tissue. A meta-analysis including all available, comparable data was used to explore important aspects of IBD inflammation, thereby validating consistent gene expression patterns.

Methods

Colon pinch biopsies from IBD patients were analysed using Illumina whole genome gene expression technology. Differential expression (DE) was identified using LIMMA linear model in the R statistical computing environment. Results were enriched for gene ontology (GO) categories. Sets of genes encoding antimicrobial proteins (AMP) and proteins involved in T helper (Th) cell differentiation were used in the interpretation of the results. All available data sets were analysed using the same methods, and results were compared on a global and focused level as t-scores.

Results

Gene expression in inflamed mucosa from UC and CD are remarkably similar. The meta-analysis confirmed this. The patterns of AMP and Th cell-related gene expression were also very similar, except for IL23A which was consistently higher expressed in UC than in CD. Un-inflamed tissue from patients demonstrated minimal differences from healthy controls.

Conclusions

There is no difference in the Th subgroup involvement between UC and CD. Th1/Th17 related expression, with little Th2 differentiation, dominated both diseases. The different IL23A expression between UC and CD suggests an IBD subtype specific role. AMPs, previously little studied, are strongly overexpressed in IBD. The presented meta-analysis provides a sound background for further research on IBD pathobiology.

Effect of tumor necrosis factor-α blockade on mucosal addressin cell-adhesion molecule-1 in Crohn's disease

BACKGROUND

Mucosal addressin cell-adhesion molecule (MAdCAM)-1, which is overexpressed on gut endothelium in active Crohn's disease (CD), promotes intestinal recruitment of integrin α(4)β(7)(*) T cells that sustain chronic inflammation. As tumor necrosis factor alpha (TNF)-α, a cytokine centrally involved in CD, modulates gut endothelial adhesion molecules, we here explored the in vivo and ex vivo effects of TNF-α blockade on MAdCAM-1 expression in CD.

METHODS

MAdCAM-1 was determined by immunoblotting in colonic biopsies collected before and 10 weeks after either infliximab or adalimumab treatment in CD patients, and in CD biopsies incubated with either infliximab or adalimumab or control IgG(1). Integrin β(7)(*) circulating T cells were analyzed by flow cytometry.

RESULTS

MAdCAM-1 significantly decreased after either infliximab or adalimumab treatment in responder but not in nonresponder patients. In parallel, an increase of circulating β(7)(*) T cells was found in responder patients only. A marked downregulation of MAdCAM-1 was observed in CD biopsies cultured with either infliximab or adalimumab in comparison to IgG(1)-treated biopsies.

CONCLUSIONS

Our findings showing that MAdCAM-1 is downregulated by TNF-α blockade point to a novel mechanism of action of anti-TNF-α antibodies in CD.

Interleukin-7 receptor blockade suppresses adaptive and innate inflammatory responses in experimental colitis

Background

Interleukin-7 (IL-7) acts primarily on T cells to promote their differentiation, survival, and homeostasis. Under disease conditions, IL-7 mediates inflammation through several mechanisms and cell types. In humans, IL-7 and its receptor (IL-7R) are increased in diseases characterized by inflammation such as atherosclerosis, rheumatoid arthritis, psoriasis, multiple sclerosis, and inflammatory bowel disease. In mice, overexpression of IL-7 results in chronic colitis, and T-cell adoptive transfer studies suggest that memory T cells expressing high amounts of IL-7R drive colitis and are maintained and expanded with IL-7. The studies presented here were undertaken to better understand the contribution of IL-7R in inflammatory bowel disease in which colitis was induced with a bacterial trigger rather than with adoptive transfer.

Methods

We examined the contribution of IL-7R on inflammation and disease development in two models of experimental colitis: Helicobacter bilis (Hb)-induced colitis in immune-sufficient Mdr1a^−/− mice and in T- and B-cell-deficient Rag2^−/− mice. We used pharmacological blockade of IL-7R to understand the mechanisms involved in IL-7R-mediated inflammatory bowel disease by analyzing immune cell profiles, circulating and colon proteins, and colon gene expression.

Results

Treatment of mice with an anti-IL-7R antibody was effective in reducing colitis in Hb-infected Mdr1a^−/− mice by reducing T-cell numbers as well as T-cell function. Down regulation of the innate immune response was also detected in Hb-infected Mdr1a^−/− mice treated with an anti-IL-7R antibody. In Rag2^−/− mice where colitis was triggered by Hb-infection, treatment with an anti-IL-7R antibody controlled innate inflammatory responses by reducing macrophage and dendritic cell numbers and their activity.

Conclusions

Results from our studies showed that inhibition of IL-7R successfully ameliorated inflammation and disease development in Hb-infected mice by controlling the expansion of multiple leukocyte populations, as well as the activity of these immune cells. Our findings demonstrate an important function of IL-7R-driven immunity in experimental colitis and indicate that the therapeutic efficacy of IL-7R blockade involves affecting both adaptive and innate immunity.

Recent advances in understanding ulcerative colitis

Ulcerative colitis, one of the two main forms of inflammatory bowel disease, is characterized by inflammation of the large bowel with constant involvement of the rectum, and a possible continuous retrograde distribution up to the cecum. Typical macroscopic lesions are mucosal ulcerations, with immune cell infiltration and cryptic abscesses at histology. Ulcerative colitis usually manifests with bloody diarrhea, is associated with a number of extra-intestinal manifestations, and may be acutely complicated by toxic megacolon. Longstanding disease may predispose to the development of colorectal cancer. Therapeutic options include mesalazine, corticosteroids, immunomodulators and biologic agents; however, if these treatments fail, the only available therapeutic choice remaining is the surgical removal of the colon. This review emphasizes novel concepts in the basic aspects of ulcerative colitis, and, in addition to the current clinical and diagnostic knowledge, it also describes new treatment options for this condition.

Optimal use and cost-effectiveness of biologic therapies in inflammatory bowel disease

Inflammatory bowel diseases (IBD), namely Crohn's disease and ulcerative colitis, are burdened by high medical costs which are mostly dependent on hospital inpatient treatment. New biologic therapies, which target specific cytokines in the inflammatory cascade leading to the intestinal lesions, including tumor necrosis factor (TNF)-α, have revolutionized the management of IBD by offering a therapeutic chance to patients in whom conventional therapies failed. However, the relatively high costs of biologic drugs, together with their potential toxicity due to infections and malignancies, have led to debate regarding their indiscriminate use in IBD patients. The purpose of this review is to deal with the optimal use and cost-effectiveness of the two main monoclonal anti-TNF-α agents currently used in the management of IBD patients, i.e. the chimeric human/murine antibody infliximab and the fully human antibody adalimumab.