The transcription factor T-bet regulates mucosal T cell activation in experimental colitis and Crohn's disease

Cytokine Networks and T-Cell Subsets in Inflammatory Bowel Diseases

Pathogenesis of the inflammatory bowel diseases (IBDs), such as ulcerative colitis (UC) and Crohn's disease (CD), involve proinflammatory changes within the microbiota, chronic immune-mediated inflammatory responses, and epithelial dysfunction. Converging data from genome-wide association studies, mouse models of IBD, and clinical trials indicate that cytokines are key effectors of both normal homeostasis and chronic inflammation in the gut. Yet many questions remain concerning the role of specific cytokines in different IBDs within distinct regions of the gut, and regarding cellular mechanisms of action. In this article, we review current and emerging concepts concerning the role of cytokines in IBD with a focus on immune regulation, T cell subsets, and potential clinical applications.

Comparative effect of 25(OH)D3 and 1,25(OH)2D3 on Th17 cell differentiation

Vitamin D is a secosteroid hormone that plays an important regulatory role in calcium homeostasis and bone metabolism. Immune cells can both produce and respond to 1,25(OH)2D3. CD4+ T cells from vitamin D receptor (VDR) KO mice produce higher levels of IFN-γ and IL-17 than their wild type counterparts, and play a crucial role in the pathogenesis of autoimmune diseases (AID). We are particularly interested in studying the effect of vitamin D on pathogenic Th17 cells in humans. We investigated the in vitro effect of 1,25(OH)2D3 and 25(OH)D3 on the differentiation and cytokine production of primary CD4+ T cells from normal donors, and cultured in Th17 polarizing conditions. Both forms of vitamin D reduced the expression of pathogenic Th17 markers and their secretion of pro-inflammatory cytokines (IL-17A, IFN-γ). Furthermore, both vitamin D forms induced an expansion of CD25hi cells and upregulated their expression of CTLA-4 and Foxp3 regulatory markers.

In vivo induction of regulatory T cells for immune tolerance in hemophilia

Current therapy for the X-linked coagulation disorder hemophilia is based on intravenous infusion of the specifically deficient coagulation factor. However, 20-30% of hemophilia A patients (factor VIII, FVIII, deficiency) generate inhibitory antibodies against FVIII. While formation of inhibitors directed against factor IX, FIX, resulting from hemophilia B treatment is comparatively rare, a serious complication that is often associated with additional immunotoxicities, e.g. anaphylaxis, occurs. Current immune tolerance protocols to eradiate inhibitors are lengthy, expensive, not effective in all patients, and there are no prophylactic tolerance regimens to prevent inhibitor formation. The outcomes of recent experiments in animal models of hemophilia demonstrate that regulatory CD4(+) T cells (Treg) are of paramount importance in controlling B cell responses to FVIII and FIX. This article reviews several novel strategies designed to in vivo induce coagulation factor-specific Treg cells and discusses the subsets of Treg that may promote immune tolerance in hemophilia. Among others, drug- and gene transfer-based protocols, lymphocyte transplant, and oral tolerance are reviewed.

T-bet Promotes Acute Graft-versus-Host Disease by Regulating Recipient Hematopoietic Cells in Mice

Beyond its critical role in T cells, T-bet regulates the functions of APCs including dendritic cells and B cells, as well as NK cells. Given that recipient APCs are essential for priming allogeneic T cells and recipient NK or T cells are able to reject allogeneic donor cells, we evaluated the role of T-bet on the host in acute graft-versus-host disease (GVHD) using murine models of allogeneic bone marrow transplantation. T-bet(-/-) recipients developed significantly milder GVHD than their wild type counterparts in MHC-mismatched or CD4-dependent minor histocompatibility Ag-mismatched models. Allogeneic donor T cells, in particular, CD4 subset, significantly reduced IFN-γ production, proliferation and migration, and caused less injury in liver and gut of T-bet(-/-) recipients. We further observed that T-bet on recipient hematopoietic cells was primarily responsible for the donor T cell response and pathogenicity in GVHD. T-bet(-/-) dendritic cells expressed higher levels of Trail, whereas they produced lower levels of IFN-γ and IL-12/23 p40, as well as chemokine CXCL9, resulting in significantly higher levels of apoptosis, less priming, and infiltration of donor T cells. Meanwhile, NK cells in T-bet(-/-) hosts partially contribute to the decreased donor T cell proliferation. Furthermore, although T-bet on hematopoietic cells was required for GVHD development, it was largely dispensable for the graft-versus-leukemia effect. Taken together with our previous findings, we propose that T-bet is a potential therapeutic target for the control of GVHD through regulating donor T cells and recipient hematopoietic cells.

Role of regulatory T cell in the pathogenesis of inflammatory bowel disease

Regulatory T (Treg) cells play key roles in various immune responses. For example, Treg cells contribute to the complex pathogenesis of inflammatory bowel disease (IBD), which includes Crohn's disease and ulcerative colitis during onset or development of that disease. Many animal models of IBD have been used to investigate factors such as pathogenic cytokines, pathogenic bacteria, and T-cell functions, including those of Treg cells. In addition, analyses of patients with IBD facilitate our understanding of the precise mechanism of IBD. This review article focuses on the role of Treg cells and outlines the pathogenesis and therapeutic strategies of IBD based on previous reports.

T-bet Regulates Natural Regulatory T Cell Afferent Lymphatic Migration and Suppressive Function

T-bet is essential for natural regulatory T cells (nTreg) to regulate Th1 inflammation, but whether T-bet controls other Treg functions after entering the inflammatory site is unknown. In an islet allograft model, T-bet(-/-) nTreg, but not induced Treg, failed to prolong graft survival as effectively as wild-type Treg. T-bet(-/-) nTreg had no functional deficiency in vitro but failed to home from the graft to draining lymph nodes (dLN) as efficiently as wild type. T-bet regulated expression of adhesion- and migration-related molecules, influencing nTreg distribution in tissues, so that T-bet(-/-) nTreg remained in the grafts rather than migrating to lymphatics and dLN. In contrast, both wild-type and T-bet(-/-) CD4(+) conventional T cells and induced Treg migrated normally toward afferent lymphatics. T-bet(-/-) nTreg displayed instability in the graft, failing to suppress Ag-specific CD4(+) T cells and prevent their infiltration into the graft and dLN. Thus, T-bet regulates nTreg migration into afferent lymphatics and dLN and consequently their suppressive stability in vivo.

Association Between Response to Etrolizumab and Expression of Integrin αE and Granzyme A in Colon Biopsies of Patients With Ulcerative Colitis

BACKGROUND & AIMS

Etrolizumab is a humanized monoclonal antibody against the β7 integrin subunit that has shown efficacy vs placebo in patients with moderate to severely active ulcerative colitis (UC). Patients with colon tissues that expressed high levels of the integrin αE gene (ITGAE) appeared to have the best response. We compared differences in colonic expression of ITGAE and other genes between patients who achieved clinical remission with etrolizumab vs those who did.

METHODS

We performed a retrospective analysis of data collected from 110 patients with UC who participated in a phase 2 placebo-controlled trial of etrolizumab, as well as from 21 patients with UC or without inflammatory bowel disease (controls) enrolled in an observational study at a separate site. Colon biopsies were collected from patients in both studies and analyzed by immunohistochemistry and gene expression profiling. Mononuclear cells were isolated and analyzed by flow cytometry. We identified biomarkers associated with response to etrolizumab. In the placebo-controlled trial, clinical remission was defined as total Mayo Clinic Score ≤2, with no individual subscore >1, and mucosal healing was defined as endoscopic score ≤1.

RESULTS

Colon tissues collected at baseline from patients who had a clinical response to etrolizumab expressed higher levels of T-cell-associated genes than patients who did not respond (P < .05). Colonic CD4(+) integrin αE(+) cells from patients with UC expressed higher levels of granzyme A messenger RNA (GZMA mRNA) than CD4(+) αE(-) cells (P < .0001); granzyme A and integrin αE protein were detected in the same cells. Of patients receiving 100 mg etrolizumab, a higher proportion of those with high levels of GZMA mRNA (41%) or ITGAE mRNA (38%) than those with low levels of GZMA (6%) or ITGAE mRNA (13%) achieved clinical remission (P < .05) and mucosal healing (41% GZMA(high) vs 19% GZMA(low) and 44% ITGAE(high) vs 19% ITGAE(low)). Compared with ITGAE(low) and GZMA(low) patients, patients with ITGAE(high) and GZMA(high) had higher baseline numbers of epithelial crypt-associated integrin αE(+) cells (P < .01 for both), but a smaller number of crypt-associated integrin αE(+) cells after etrolizumab treatment (P < .05 for both). After 10 weeks of etrolizumab treatment, expression of genes associated with T-cell activation and genes encoding inflammatory cytokines decreased by 40%-80% from baseline (P < .05) in patients with colon tissues expressing high levels of GZMA at baseline.

CONCLUSIONS

Levels of GZMA and ITGAE mRNAs in colon tissues can identify patients with UC who are most likely to benefit from etrolizumab; expression levels decrease with etrolizumab administration in biomarker(high) patients. Larger, prospective studies of markers are needed to assess their clinical value.

A Small Molecule Inhibitor of ITK and RLK Impairs Th1 Differentiation and Prevents Colitis Disease Progression

In T cells, the Tec kinases IL-2-inducible T cell kinase (ITK) and resting lymphocyte kinase (RLK) are activated by TCR stimulation and are required for optimal downstream signaling. Studies of CD4(+) T cells from Itk(-/-) and Itk(-/-)Rlk(-/-) mice have indicated differential roles of ITK and RLK in Th1, Th2, and Th17 differentiation and cytokine production. However, these findings are confounded by the complex T cell developmental defects in these mice. In this study, we examine the consequences of ITK and RLK inhibition using a highly selective and potent small molecule covalent inhibitor PRN694. In vitro Th polarization experiments indicate that PRN694 is a potent inhibitor of Th1 and Th17 differentiation and cytokine production. Using a T cell adoptive transfer model of colitis, we find that in vivo administration of PRN694 markedly reduces disease progression, T cell infiltration into the intestinal lamina propria, and IFN-γ production by colitogenic CD4(+) T cells. Consistent with these findings, Th1 and Th17 cells differentiated in the presence of PRN694 show reduced P-selectin binding and impaired migration to CXCL11 and CCL20, respectively. Taken together, these data indicate that ITK plus RLK inhibition may have therapeutic potential in Th1-mediated inflammatory diseases.

Reduced incidence of Crohn's disease in systemic sclerosis: a nationwide population study

Background

To date, there has been no studies to evaluate the incidence of Crohn’s disease in systemic sclerosis patients. The goals of this study were to evaluate the incidence of Crohn’s disease and its relationship with sex and age in patients with systemic sclerosis.

Methods

We enrolled patients with systemic sclerosis and controls from Taiwan’s Registry of Catastrophic Illness Database and National Health Insurance Research Database. Every systemic sclerosis patient was matched to at most three controls by sex, age, month and year of initial diagnosis of systemic sclerosis. The standardized incidence ratio (SIR) of Crohn’s disease in systemic sclerosis patients, and 95 % confidence interval (95 % CI) were calculated. Cox hazard regression was used to calculate the hazard ratio (HR).

Results

The study enrolled 2,829 patients with systemic sclerosis and 8,257 controls. Male and female patients with systemic sclerosis both had lower rates of incident Crohn’s disease (SIR: 0.18, 95 % CI = 0.05–0.62; SIR: 0.10, 95 % CI = 0.05–0.21, respectively). The risk of incident Crohn’s disease in systemic sclerosis was still lower than in controls when we stratified the patients according to their ages. In Cox hazard regression, the hazard rates of Crohn’s disease were lower in systemic sclerosis patients after adjusting for genders and ages (HR: 0.12, 95 % CI = 0.06–0.21, p < 0.001).

Conclusions

Systemic sclerosis is associated with decreased incidence of, irrespective of sex and age of the patients.

A breakthrough in probiotics: Clostridium butyricum regulates gut homeostasis and anti-inflammatory response in inflammatory bowel disease

Intestinal immune homeostasis is regulated by gut microbiota, including beneficial and pathogenic microorganisms. Imbalance in gut bacterial constituents provokes host proinflammatory responses causing diseases such as inflammatory bowel disease (IBD). The development of next-generation sequencing technology allows the identification of microbiota alterations in IBD. Several studies have shown reduced diversity in the gut microbiota of patients with IBD. Advances in gnotobiotic technology have made possible analysis of the role of specific bacterial strains in immune cells in the intestine. Using these techniques, we have shown that Clostridium butyricum as a probiotic induces interleukin-10-producing macrophages in inflamed mucosa via the Toll-like receptor 2/myeloid differentiation primary response gene 88 pathway to prevent acute experimental colitis. In this review, we focus on the new approaches for the role of specific bacterial strains in immunological responses, as well as the potential of bacterial therapy for IBD treatments.

Huangqin-Tang Ameliorates TNBS-Induced Colitis by Regulating Effector and Regulatory CD4(+) T Cells

Huangqin-Tang decoction (HQT) is a classic traditional Chinese herbal formulation that is widely used to ameliorate the symptoms of gastrointestinal disorders, including inflammatory bowel disease (IBD). This study was designed to investigate the therapeutic potential and immunological regulatory activity of HQT in experimental colitis in rats. Using an animal model of colitis by intrarectally administering 2,4,6-trinitrobenzenesulfonic acid (TNBS), we found that administration of HQT significantly inhibited the severity of TNBS-induced colitis in a dose-dependent manner. In addition, treatment with HQT produced better results than that with mesalazine, as shown by improvedweight loss bleeding and diarrhoea scores, colon length, and intestinal inflammation. As for potential immunological regulation of HQT action, the percentages of Th1 and Th17 cells were reduced, but those Th2 and Treg cells were enhanced in LPMCs after HQT treatment. Additionally, HQT lowered the levels of Th1/Th17-associated cytokines but increased production of Th2/Treg-associated cytokines in the colon and MLNs. Furthermore, we observed a remarkable suppression of the Th1/Th17-associated transcription factors T-bet and ROR-γt. However, expression levels of the Th2/Treg-associated transcription factors GATA-3 and Foxp3 were enhanced during treatment with HQT. Our results suggest that HQT has the therapeutic potential to ameliorate TNBS-induced colitis symptoms. This protective effect is possibly mediated by its effects on CD4(+) T cells subsets.

CD8(+)IL-17(+) T Cells Mediate Neutrophilic Airway Obliteration in T-bet-Deficient Mouse Lung Allograft Recipients

Acute cellular rejection is a known risk factor for the development of obliterative bronchiolitis, which limits the long-term survival of lung transplant recipients. However, the T cell effector mechanisms in both of these processes remain incompletely understood. Using the mouse orthotopic lung transplant model, we investigated whether C57BL/6 T-bet(-/-) recipients of major histocompatibility complex (MHC)-mismatched BALB/c lung grafts develop rejection pathology and allospecific cytokine responses that differ from wild-type mice. T-bet(-/-) recipients demonstrated vigorous allograft rejection at 10 days, characterized by neutrophilic inflammation and predominantly CD8(+) T cells producing allospecific IL-17 and/or IFN-γ, in contrast to IFN-γ-dominant responses in WT mice. CD4(+) T cells produced IL-17 but not IFN-γ responses in T-bet(-/-) recipients, in contrast to WT controls. Costimulation blockade using anti-CD154 Ab significantly reduced allospecific CD8(+)IFN-γ(+) responses in both T-bet(-/-) and WT mice but had no attenuating effect on lung rejection pathology in T-bet(-/-) recipients or on the development of obliterative airway inflammation that occurred only in T-bet(-/-) recipients. However, neutralization of IL-17A significantly attenuated costimulation blockade-resistant rejection pathology and airway inflammation in T-bet(-/-) recipients. In addition, CXCL1 (neutrophil chemokine) was increased in T-bet(-/-) allografts, and IL-17 induced CXCL1 from mouse lung epithelial cells in vitro. Taken together, our data show that T-bet-deficient recipients of complete MHC-mismatched lung allografts develop costimulation blockade-resistant rejection characterized by neutrophilia and obliterative airway inflammation that is predominantly mediated by CD8(+)IL-17(+) T cells. Our data support T-bet-deficient mouse recipients of lung allografts as a viable animal model to study the immunopathogenesis of small airway injury in lung transplantation.

Bone Morphogenetic Protein Signaling Regulates Development and Activation of CD4(+) T Cells

Bone morphogenetic proteins (BMPs) are growth factors belonging to the TGF-β (transforming growth factor β) superfamily. BMPs were found to regulate multiple cell processes such as proliferation, survival, differentiation, and apoptosis. They were originally described to play a pivotal role in inducing bone, cartilage, ligament, and tendon formation at both heterotopic and orthotopic sites but were found to play a significant role in embryogenesis and development of multiple tissues and organs. Activities of BMPs are regulated by a number of secreted proteins, which modulate their availability to bind cellular receptors. The functions of individual BMPs are highly redundant due to binding the same receptors and inducing overlapping signal transduction pathways. Recently, BMPs were found to regulate cells of the innate and adaptive immune system. BMPs are involved in thymic development of T cells at the early, double negative, as well as later, double positive, stages of thymopoesis. They specifically modulate thymic development of regulatory T cells (T(reg)). In the periphery, BMPs affect T cell activation, promoting generation of T(reg) cells. We found that mice deficient for one of the receptors activated by BMPs demonstrated slower growth of transplantable melanoma tumors.

The TGF-β superfamily in dendritic cell biology

The TGF-β superfamily consists of a large group of pleiotropic cytokines that are involved in the regulation of many developmental, physiological and pathological processes. Dendritic cells are antigen-presenting cells that play a key role in innate and adaptive immune responses. Dendritic cells have a complex relationship with the TGF-β cytokine superfamily being both source and targets for many of these cytokines. Some TGF-β family members are expressed by dendritic cells and modulate immune responses, for instance through the induction of T cell polarization. Others play a crucial role in the development and function of the different dendritic cell subsets. This review summarizes the current knowledge on the role of TGF-β family cytokines in dendritic cell biology, focusing on TGF-β as well as on other, less characterized, members of these important immune mediators.

Crohn’s disease with gastroduodenal involvement: Diagnostic approach

Crohn’s disease (CD) is a chronic idiopathic inflammatory disease of gastrointestinal tract characterized by segmental and transmural involvement of gastrointestinal tract. Ileocolonic and colonic/anorectal is a most common and account for 40% of cases and involvement of small intestine is about 30%. Isolated involvement of stomach is an extremely unusual presentation of the disease accounting for less than 0.07% of all gastrointestinal CD. To date there are only a few documented case reports of adults with isolated gastric CD and no reports in the pediatric population. The diagnosis is difficult to establish in such cases with atypical presentation. In the absence of any other source of disease and in the presence of nonspecific upper gastrointestinal endoscopy and histological findings, serological testing can play a vital role in the diagnosis of atypical CD. Recent studies have suggested that perinuclear anti-neutrophil cytoplasmic antibody and anti-Saccharomycescervisia antibody may be used as additional diagnostic tools. The effectiveness of infliximab in isolated gastric CD is limited to only a few case reports of adult patients and the long-term outcome is unknown.

Th17 cells give rise to Th1 cells that are required for the pathogenesis of colitis

Th17 cells reactive to the enteric microbiota are central to the pathogenesis of certain types of inflammatory bowel disease. However, Th17 cells display substantial developmental plasticity, such that some progeny of Th17 cell precursors retain a predominantly IL-17A(+) phenotype, whereas others extinguish IL-17 expression and acquire expression of IFN-γ, giving rise to "Th1-like" cells. It remains unclear what role these subsets play in inflammatory bowel disease. Using a Th17 transfer model of colitis, we found that IFN-γ-deficient Th17 cells retained an IL-17A(+) phenotype and were unable to induce colitis in recipients. Development of disease required the transition of a subset of Th17 precursors to Th1-like cells and was contingent on the expression of both Stat4 and T-bet, but not the IL-12 or IFN-γ receptors. Moreover, Th17 cells could provide "help" for the development of pathogenic Th1 cells from naïve precursors. These results indicate that Th17 cells are potent mediators of colitis pathogenesis by dual mechanisms: by directly transitioning to Th1-like cells and by supporting the development of classic Th1 cells.

The development and in vivo function of T helper 9 cells

The specialized cytokine secretion profiles of T helper (TH) cells are the basis for a focused and efficient immune response. On the twentieth anniversary of the first descriptions of the cytokine signals that promote the differentiation of interleukin-9 (IL-9)-secreting T cells, this Review focuses on the extracellular signals and the transcription factors that promote the development of what we now term TH9 cells, which are characterized by the production of this cytokine. We summarize our current understanding of the contribution of TH9 cells to both effective immunity and immunopathological disease, and we propose that TH9 cells could be targeted for the treatment of allergic and autoimmune disease.

Qualitative differences in brain-infiltrating T cells are associated with a fatal outcome in mice infected with Japanese encephalitis virus

Japanese encephalitis (JE) is the most important form of viral encephalitis in Asia. The critical factors determining mortality and severity of JE virus (JEV) infection remain unclear. We identified brain-infiltrating T cells associated with a fatal outcome of JEV infection in mice. Dying mice were defined as those that lost more than 25 % of their body weight by day 13 and died by day 21, while surviving mice were defined as those that lost less than 10 % by day 13, based on the result of the survival time course study. Two groups of five mice that demonstrated brain virus titers of >1 × 10(6) pfu/g were randomly selected from the dying and surviving groups and used in the analyses. Cytokine patterns in brains were first examined, revealing a higher ratio of Th1-related cytokine genes in dying mice. The expression levels of CD3, CD8, CD25, and CD69 increased in JEV-infected mice relative to mock-infected mice. However, expression levels of these cell-surface markers did not differ between the two groups. T-cell receptor (TCR) usage and complementary determining region 3 (CDR3) sequences were analyzed in the brain-infiltrating T cells. T cells expressing VA8-1, VA10-1, and VB2-1 increased in both groups. However, the dominant T-cell clones as defined by CDR3 amino acid sequence differed between the two groups. The results indicate that the outcome of JEV infection, death or survival, was determined by qualitative differences in infiltrating T-cell clones with unique CDR3 amino acid sequences.

T-bet Expression by Foxp3(+) T Regulatory Cells is Not Essential for Their Suppressive Function in CNS Autoimmune Disease or Colitis

Accumulation of T regulatory (Treg) cells within the central nervous system (CNS) during experimental autoimmune encephalomyelitis (EAE) is essential for the resolution of disease. CNS Treg cells have been shown to uniformly express the Th1-associated molecules, T-bet and CXCR3. Here, we report that the expression of T-bet is not required for the function of these Treg within the CNS. Using mice that lacked T-bet expression specifically within the Treg compartment, we demonstrate that there was no deficit in Treg recruitment into the CNS during EAE and no difference in the resolution of disease compared to control mice. T-bet deficiency did not impact on the in vitro suppressive capacity of Treg. Transfer of T-bet-deficient Treg was able to suppress clinical signs of either EAE or colitis. These observations demonstrate that, although Treg can acquire characteristics associated with pathogenic T effector cells, this process is not necessarily required for their suppressive capacity and the resolution of autoimmune inflammation.

Th17 differentiation and their pro-inflammation function

CD4(+) T helper cells are classical but constantly reinterpreted T-cell subset, playing critical roles in a diverse range of inflammatory responses or diseases. Depending on the cytokines they release and the immune responses they mediate, CD4(+) T cells are classically divided into two major cell populations: Th1 and Th2 cells. However, recent studies challenged this Th1/Th2 paradigm by discovering several T-helper cell subsets with specific differentiation program and functions, including Th17 cells, Treg cells, and Tfh cells. In this chapter, we summarize the current understanding and recent progresses on the Th17 lineage differentiation and its effector impacts on variety of inflammatory responses or disease pathogenesis.

Oral delivery of prolyl hydroxylase inhibitor: AKB-4924 promotes localized mucosal healing in a mouse model of colitis

BACKGROUND

Pharmacological induction of hypoxia-inducible factor (HIF), a global transcriptional regulator of the hypoxic response, by prolyl hydroxylase inhibitors (PHDi) is protective in murine models of colitis, and epithelial cells are critical for the observed therapeutic efficacy. Because systemic HIF activation may lead to potentially negative off-target effects, we hypothesized that targeting epithelial HIF through oral delivery of PHDi would be sufficient to protect against colitis in a mouse model.

METHODS

Using a chemically induced trinitrobenzene sulfonic acid murine model of colitis, we compared the efficacy of oral and intraperitoneal (i.p.) delivery of the PHDi; AKB-4924 in preventing colitis, as measured by endoscopy, histology, barrier integrity, and immune profiling. Furthermore, we measured potential off-target effects, examining HIF and HIF target genes in the heart and kidney, as well as erythropoietin and hematocrit levels.

RESULTS

Oral administration of AKB-4924 exhibited mucosal protection comparable i.p. dosing. Oral delivery of PHDi led to reduced colonic epithelial HIF stabilization compared with i.p. delivery, but this was still sufficient to induce transcription of downstream HIF targets. Furthermore, oral delivery of PHDi led to reduced stabilization of HIF and activation of HIF targets in extraintestinal organs.

CONCLUSIONS

Oral delivery of PHDi therapies to this intestinal mucosa protects against colitis in animal models and represents a potential therapeutic strategy for inflammatory bowel disease, which also precludes unwanted extraintestinal effects.

miR-148a is upregulated by Twist1 and T-bet and promotes Th1-cell survival by regulating the proapoptotic gene Bim

Repeatedly activated T helper 1 (Th1) cells present during chronic inflammation can efficiently adapt to the inflammatory milieu, for example, by expressing the transcription factor Twist1, which limits the immunopathology caused by Th1 cells. Here, we show that in repeatedly activated murine Th1 cells, Twist1 and T-bet induce expression of microRNA-148a (miR-148a). miR-148a regulates expression of the proapoptotic gene Bim, resulting in a decreased Bim/Bcl2 ratio. Inhibition of miR-148a by antagomirs in repeatedly activated Th1 cells increases the expression of Bim, leading to enhanced apoptosis. Knockdown of Bim expression by siRNA in miR-148a antagomir-treated cells restores viability of the Th1 cells, demonstrating that miR-148a controls survival by regulating Bim expression. Thus, Twist1 and T-bet not only control the differentiation and function of Th1 cells, but also their persistence in chronic inflammation.

Experimental Models of Inflammatory Bowel Diseases

The understanding of the intestinal inflammation occurring in the inflammatory bowel diseases (IBD) has been immeasurably advanced by the development of the now numerous murine models of intestinal inflammation. The usefulness of this research tool in IBD studies has been enabled by our improved knowledge of mucosal immunity and thus our improved ability to interpret the complex responses of mice with various causes of colitis; in addition, it has been powered by the availability of models in which the mice have specific genetic and/or immunologic defects that can be related to the origin of the inflammation. Finally, and more recently, it has been enhanced by our newly acquired ability to define the intestinal microbiome under various conditions and thus to understand how intestinal microorganisms impact on inflammation. In this brief review of murine models of intestinal inflammation we focus mainly on the most often used models that are, not incidentally, also the models that have yielded major insights into IBD pathogenesis.

The oncoprotein and transcriptional regulator Bcl-3 governs plasticity and pathogenicity of autoimmune T cells

Bcl-3 is an atypical member of the IκB family that modulates transcription in the nucleus via association with p50 (NF-κB1) or p52 (NF-κB2) homodimers. Despite evidence attesting to the overall physiologic importance of Bcl-3, little is known about its cell-specific functions or mechanisms. Here we demonstrate a T-cell-intrinsic function of Bcl-3 in autoimmunity. Bcl-3-deficient T cells failed to induce disease in T cell transfer-induced colitis and experimental autoimmune encephalomyelitis. The protection against disease correlated with a decrease in Th1 cells that produced the cytokines IFN-γ and GM-CSF and an increase in Th17 cells. Although differentiation into Th1 cells was not impaired in the absence of Bcl-3, differentiated Th1 cells converted to less-pathogenic Th17-like cells, in part via mechanisms involving expression of the RORγt transcription factor. Thus, Bcl-3 constrained Th1 cell plasticity and promoted pathogenicity by blocking conversion to Th17-like cells, revealing a unique type of regulation that shapes adaptive immunity.

Diverse roles for T-bet in the effector responses required for resistance to infection

The transcription factor T-bet has been most prominently linked to NK and T cell production of IFN-γ, a cytokine required for the control of a diverse array of intracellular pathogens. Indeed, in mice challenged with the parasite Toxoplasma gondii, NK and T cell responses are characterized by marked increases of T-bet expression. Unexpectedly, T-bet(-/-) mice infected with T. gondii develop a strong NK cell IFN-γ response that controls parasite replication at the challenge site, but display high parasite burdens at secondary sites colonized by T. gondii and succumb to infection. The loss of T-bet had a modest effect on T cell production of IFN-γ but did not impact on the generation of parasite-specific T cells. However, the absence of T-bet resulted in lower T cell expression of CD11a, Ly6C, KLRG-1, and CXCR3 and fewer parasite-specific T cells at secondary sites of infection, associated with a defect in parasite control at these sites. Together, these data highlight T-bet-independent pathways to IFN-γ production and reveal a novel role for this transcription factor in coordinating the T cell responses necessary to control this infection in peripheral tissues.

Regulation of inflammatory transcription factors by heat shock protein 70 in primary cultured astrocytes exposed to oxygen-glucose deprivation

Inflammation is an important event in ischemic injury. These immune responses begin with the expression of pro-inflammatory genes modulating transcription factors, such as nuclear factor-κB (NF-κB), activator protein-1 (AP-1), and signal transducers and activator of transcription-1 (STAT-1). The 70-kDa heat shock protein (Hsp70) can both induce and arrest inflammatory reactions and lead to improved neurological outcome in experimental brain injury and ischemia. Since Hsp70 are induced under heat stress, we investigated the link between Hsp70 neuroprotection and phosphorylation of inhibitor of κB (IκB), c-Jun N-terminal kinases (JNK) and p38 through co-immunoprecipitation and enzyme-linked immunosorbent assay (ELISA) assay. Transcription factors and pro-inflammatory genes were quantified by immunoblotting, electrophoretic-mobility shift assay and reverse transcription-polymerase chain reaction assays. The results showed that heat stress led to Hsp70 overexpression which rendered neuroprotection after ischemia-like injury. Overexpression Hsp70 also interrupts the phosphorylation of IκB, JNK and p38 and blunts DNA binding of their transcription factors (NF-κB, AP-1 and STAT-1), effectively downregulating the expression of pro-inflammatory genes in heat-pretreated astrocytes. Taken together, these results suggest that overexpression of Hsp70 may protect against brain ischemia via an anti-inflammatory mechanism by interrupting the phosphorylation of upstream of transcription factors.

The transcription factor T-bet is induced by IL-15 and thymic agonist selection and controls CD8αα(+) intraepithelial lymphocyte development

CD8αα(+) intraepithelial lymphocytes (IELs) are instrumental in maintaining the epithelial barrier in the intestine. Similar to natural killer cells and other innate lymphoid cells, CD8αα(+) IELs constitutively express the T-box transcription factor T-bet. However, the precise role of T-bet for the differentiation or function of IELs is unknown. Here we show that mice genetically deficient for T-bet lacked both TCRαβ(+) and TCRγδ(+) CD8αα(+) IELs and thus are more susceptible to chemically induced colitis. Although T-bet was induced in thymic IEL precursors (IELPs) as a result of agonist selection and interleukin-15 (IL-15) receptor signaling, it was dispensable for the generation of IELPs. Subsequently, T-bet was required for the IL-15-dependent activation, differentiation, and expansion of IELPs in the periphery. Our study reveals a function of T-bet as a central transcriptional regulator linking agonist selection and IL-15 signaling with the emergence of CD8αα(+) IELs.

T-cell-restricted T-bet overexpression induces aberrant hematopoiesis of myeloid cells and impairs function of macrophages in the lung

Although overexpression of T-bet, a master transcription factor in type-1 helper T lymphocytes, has been reported in several hematologic and immune diseases, its role in their pathogenesis is not fully understood. In the present study, we used transgenic model mice (T-bet(tg/wt) and T-bet(tg/tg)) to investigate the effects of T-bet overexpression selectively in T lymphocytes on the development of hematologic and immune diseases. The results showed that T-bet overexpression in T cells spontaneously induced maturation arrest in the mononuclear phagocyte lineage, as well as spontaneous dermatitis and pulmonary alveolar proteinosis (PAP)-like disease in T-bet(tg/wt) and T-bet(tg/tg) mice, respectively. T-bet(tg/tg) alveoli with the PAP phenotype showed remarkable reorganization of alveolar mononuclear phagocyte subpopulations and impaired function, in addition to augmented T-cell infiltration. In addition, PAP development in T-bet(tg/tg) mice was found to be associated with increased migration of myeloid cells from the bone marrow into the peripheral blood. These findings reveal an unexpected link between T-bet overexpression in T lymphocytes and the development of PAP caused by reorganization of mononuclear phagocytes in the lung, and provide new insight into the molecular pathogenesis of secondary PAP accompanied by hematologic disorders.

Classical Th1 cells obtain colitogenicity by co-existence of RORγt-expressing T cells in experimental colitis

BACKGROUND

Both Th1 and Th17 cell types are involved in the pathogenesis of chronic intestinal inflammation. We recently demonstrated that retinoid-related orphan receptor gamma t (RORγt)-expressing Th17 cells are progenitor cells for alternative Th1 cells, which have the potential to induce colitis. However, the involvement of classical Th1 (cTh1) cells generated directly from naive T cells without RORγt expression in the pathogenesis of colitis remains poorly understood.

METHODS

We performed a series of in vivo experiments using a murine chronic colitis model induced by adoptive transfer of splenic CD4CD45RB(high) T cells obtained from wild-type, RORγt(gfp/gfp), or RORγt(gfp/gfp) mice into RAG-2(-/-) mice.

RESULTS

RAG-2(-/-) mice receiving transfer of in vitro-manipulated RORγt(gfp/gfp) Th1 cells developed colitis. RAG-2(-/-) mice co-transferred with splenic CD4CD45RB(high) T cells obtained from wild-type mice and RORγt(gfp/gfp) mice developed colitis with a significant increase in RORγt cTh1 cell numbers when compared with noncolitic mice transferred with splenic CD4CD45RB(high) T cells obtained from RORγt(gfp/gfp) mice. Furthermore, RAG-2(-/-) mice transferred with in vivo-manipulated RORγt(gfp/gfp) cTh1 cells developed colitis with a significant increase in RORγt(gfp/gfp) cTh1 cell numbers.

CONCLUSIONS

These findings indicate that both alternative Th1 cells and cTh1 cells have the potential to be colitogenic in an adaptive transfer model. The development of cTh1 cells was dependent on the co-existence of RORγt-expressing T cells, suggesting a critical role for the interactions of these cell types in the development of chronic intestinal inflammation.

Transcription factor T-bet regulates intraepithelial lymphocyte functional maturation

The intestinal epithelium harbors large populations of activated and memory lymphocytes, yet these cells do not cause tissue damage in the steady state. We investigated how intestinal T cell effector differentiation is regulated upon migration to the intestinal epithelium. Using gene loss- and gain-of-function strategies, as well as reporter approaches, we showed that cooperation between the transcription factors T-bet and Runx3 resulted in suppression of conventional CD4(+) T helper functions and induction of an intraepithelial lymphocyte (IEL) program that included expression of IEL markers such as CD8αα homodimers. Interferon-γ sensing and T-bet expression by CD4(+) T cells were both required for this program, which was distinct from conventional T helper differentiation but shared by other IEL populations, including TCRαβ(+)CD8αα(+) IELs. We conclude that the gut environment provides cues for IEL maturation through the interplay between T-bet and Runx3, allowing tissue-specific adaptation of mature T lymphocytes.

TH9 cells that express the transcription factor PU.1 drive T cell-mediated colitis via IL-9 receptor signaling in intestinal epithelial cells

The molecular checkpoints that drive inflammatory bowel diseases are incompletely understood. Here we found more T cells expressing the transcription factor PU.1 and interleukin 9 (IL-9) in patients with ulcerative colitis. In an animal model, citrine reporter mice had more IL-9-expressing mucosal T cells in experimental oxazolone-induced colitis. IL-9 deficiency suppressed acute and chronic colitis. Mice with PU.1 deficiency in T cells were protected from colitis, whereas treatment with antibody to IL-9 suppressed colitis. Functionally, IL-9 impaired intestinal barrier function and prevented mucosal wound healing in vivo. Thus, our findings suggest that the TH9 subset of helper T cells serves an important role in driving ulcerative colitis by regulating intestinal epithelial cells and that TH9 cells represent a likely target for the treatment of chronic intestinal inflammation.

Deubiquitination and stabilization of T-bet by USP10

The T-box transcriptional factor T-bet is crucial in the development, differentiation and function of Th1 cells. It drives Th1 immune response primarily through promoting expression of Th1 hallmark cytokine IFN-γ. Although T-bet was found associated with many immune-mediated diseases such as asthma and systemic sclerosis, little is known about the regulation of T-bet stability and function. Here we identified USP10, a carboxyl-terminal ubiquitin-processing protease, could interact with T-bet in the nucleus. Overexpression of USP10 directly inhibited T-bet ubiquitination and increased the expression of T-bet. We further confirmed Quercetin, a reported inhibitor of T-bet, could target USP10. Quercetin treatment downregulated USP10 and promoted T-bet degradation in a proteasome dependent way. Moreover, we found USP10 expression was upregulated in asthmatic patient PBMC, suggesting USP10 may maintain high level of T-bet and IFN-γ to fight against Th2-dominated inflammation.

The role of protein modifications of T-bet in cytokine production and differentiation of T helper cells

T-Bet (T-box protein expressed in T cells, also called as TBX21) was originally cloned as a key transcription factor involved in the commitment of T helper (Th) cells to the Th1 lineage. T-Bet directly activates IFN-γ gene transcription and enhances development of Th1 cells. T-Bet simultaneously modulates IL-2 and Th2 cytokines in an IFN-γ-independent manner, resulting in an attenuation of Th2 cell development. Numerous studies have demonstrated that T-bet plays multiple roles in many subtypes of immune cells, including B cell, dendritic cells, natural killer (NK) cells, NK T cells, and innate lymphoid cells. Therefore, T-bet is crucial for the development and coordination of both innate and adaptive immune responses. To fulfill these multiple roles, T-bet undergoes several posttranslational protein modifications, such as phosphorylation at tyrosine, serine, and threonine residues, and ubiquitination at lysine residues, which affect lineage commitment during Th cell differentiation. This review presents a current overview of the progress made in understanding the roles of various types of T-bet protein modifications in the regulation of cytokine production during Th cell differentiation.

Inflammation programs self-reactive CD8+ T cells to acquire T-box-mediated effector function but does not prevent deletional tolerance

CD8(+) T cells must detect foreign antigens and differentiate into effector cells to eliminate infections. But, when self-antigen is recognized instead, mechanisms of peripheral tolerance prevent acquisition of effector function to avoid autoimmunity. These distinct responses are influenced by inflammatory and regulatory clues from the tissue environment, but the mechanism(s) by which naive T cells interpret these signals to generate the appropriate immune response are unclear. The identification of the molecules operative in these cell-fate decisions is crucial for developing new treatment options for patients with cancer or autoimmunity, where manipulation of T cell activity is desired to alter the course of disease. With the use of an in vivo murine model to examine CD8(+) T cell responses to healthy self-tissue, we correlated self-tolerance with a failure to induce the T-box transcription factors T-bet and Eomes. However, inflammation associated with acute microbial infection induced T-bet and Eomes expression and promoted effector differentiation of self-reactive T cells under conditions that normally favor tolerance. In the context of a Listeria infection, these functional responses relied on elevated T-bet expression, independent of Eomes. Alternatively, infection with LCMV induced higher Eomes expression, which was sufficient in the absence of T-bet to promote effector cytokine production. Our results place T-box transcription factors at a molecular crossroads between CD8(+) T cell anergy and effector function upon recognition of peripheral self-antigen, and suggest that inflammation during T cell priming directs these distinct cellular responses.

Cytokines in inflammatory bowel disease

Cytokines have a crucial role in the pathogenesis of inflammatory bowel diseases (IBDs), such as Crohn's disease and ulcerative colitis, where they control multiple aspects of the inflammatory response. In particular, the imbalance between pro-inflammatory and anti-inflammatory cytokines that occurs in IBD impedes the resolution of inflammation and instead leads to disease perpetuation and tissue destruction. Recent studies suggest the existence of a network of regulatory cytokines that has important implications for disease progression. In this Review, we discuss the role of cytokines produced by innate and adaptive immune cells, as well as their relevance to the future therapy of IBD.

Overexpression of ATP-activated P2X7 receptors in the intestinal mucosa is implicated in the pathogenesis of Crohn's disease

BACKGROUND

Extracellular nucleotides released in conditions of cell stress alert the immune system from tissue injury or inflammation. We hypothesized that the P2X7 receptor (P2X7-R) could regulate key elements in inflammatory bowel disease pathogenesis.

METHODS

Colonoscopy samples obtained from patients with Crohn's disease (CD), ulcerative colitis, and controls were used to analyze P2X7-R expression by RT and real-time PCR, immunohistochemistry, and confocal microscopy. Inflammatory response was determined by the levels of cytokines by enzyme-linked immunosorbent assay in cultures of intestinal explants. Apoptosis was determined by the TUNEL assay. P2X7-R C57BL/6 mice were treated with trinitrobenzene sulfonic acid or dextran sulfate sodium (DSS) for inducing colitis.

RESULTS

P2X7-R was expressed in higher levels in inflamed CD epithelium and lamina propria, where it colocalizes more with dendritic cells and macrophages. Basal levels of P2X7-R mRNA were higher in CD inflamed mucosa compared with noninflamed CD and controls and were upregulated after interferon-γ in controls. Apoptotic rates were higher in CD epithelium and lamina propria compared with ulcerative colitis and controls. Levels of tumor necrosis factor-α, interleukin (IL)-1β, and IL-17 were higher, whereas IL-10 was lower in CD compared with controls. Levels of tumor necrosis factor-α-α and interleukin-1β increased after adenosine-triphosphate and decreased after KN62 treatment in CD. P2X7-R animals did not develop trinitrobenzene sulfonic acid or DSS colitis.

CONCLUSIONS

The upregulation of P2X7-R in CD inflamed mucosa is consistent with the involvement of purinoceptors in inflammation and apoptosis. These observations may implicate purinergic signaling in the pathogenesis of intestinal inflammation, and the P2X7-R may represent a novel therapeutic target in CD.

Cytokine IL-6 is required in Citrobacter rodentium infection-induced intestinal Th17 responses and promotes IL-22 expression in inflammatory bowel disease

Citrobacter rodentium (C. rodentium) infection is a widely used murine model to mimic human enteric bacteria infection and inflammatory bowel disease (IBD). In this model, interleukin (IL)‑17A plays critical roles in increasing chemokine and cytokine production in various tissues to recruit innate cells, including monocytes and neutrophils, to the local site of infection. However, the source of IL‑17A remains unclear, as the majority of cell types produce IL‑17A, including intestinal endothelium cells, innate immune cells and CD4+ T cells in disease development. In the current study, wild‑type B6 mice were treated with C. rodentium and the CD4+ Th17 cell subset was observed as being specifically increased in Peyer's patches (PP), but not in mesenteric draining lymph nodes. Furthermore, the research suggested that the differentiation and activation of Th17 cells in PP were dependent on the inflammatory cytokine IL‑6, as blocking IL‑6 signaling with neutralizing antibodies decreased Th17 cells and resulted in the mice being more susceptible to C. rodentium infection. These results confirmed that the Th17 cell subset was specifically activated in PP and demonstrated that IL‑6 is required in Th17 cell activation, which are important to the clinical treatment of IBD.

Endotoxicity of lipopolysaccharide as a determinant of T-cell-mediated colitis induction in mice

BACKGROUND & AIMS

The intestinal microbiota is an important determinant of the mucosal response. In patients with inflammatory bowel diseases, the mucosal immune system has inappropriate interactions with the intestinal microbiota. We investigated how the composition of the intestinal microbiota affects its endotoxicity and development of colitis in mice.

METHODS

Germ-free C57BL/6J-Rag(1tm1Mom) (Rag1(-/-)) mice were colonized with 2 different types of complex intestinal microbiota. Colitis was induced in Rag1(-/-) mice by transfer of CD4(+)CD62L(+) T cells from C57BL/6J mice. Colonic tissues were collected and used for histologic analysis and cell isolation. Activation of lamina propria dendritic cells and T cells was analyzed by flow cytometry.

RESULTS

After transfer of CD4(+)CD62L(+) T cells, mice with intestinal Endo(lo) microbiota (a low proportion of Enterobacteriaceae, high proportion of Bacteroidetes, and low endotoxicity) maintained mucosal immune homeostasis, and mice with highly endotoxic Endo(hi) microbiota (a high proportion of Enterobacteriaceae and low proportion of Bacteroidetes) developed colitis. To determine whether the effects of Endo(hi) microbiota were related to the higher endotoxic activity of lipopolysaccharide (LPS), we compared LPS from Enterobacteriaceae with that of Bacteroidetes. Administration of Escherichia coli JM83 (wild-type LPS) to the mice exacerbated colitis, and Escherichia coli JM83 + htrBPG (mutated LPS, with lower endotoxicity, similar to that of Bacteroidetes) prevented development of colitis after transfer of the T cells to mice.

CONCLUSIONS

The endotoxicity of LPS produced by the intestinal microbiota is a determinant of whether mice develop colitis after transfer of CD4(+)CD62L(+) T cells. This finding might aid the design of novel biologics or probiotics to treat inflammatory bowel disease.

Conditioned mesenchymal stem cells produce pleiotropic gut trophic factors

BACKGROUND

Although mounting evidence implicates mesenchymal stem cells (MSCs) in intestinal tissue repair, controversy remains regarding the engraftment, proliferation, and differentiation for repopulating MSCs in recipient tissues. Therefore, we investigated the paracrine and/or endocrine role of MSCs in experimental colitis.

METHODS

We analyzed the therapeutic effects of MSC-conditioned medium (MSC-CM) on dextran sulfate sodium (DSS)- or 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis. We investigated the effects of MSC-CM on the epithelial cell viability, mobility, cell cycle, and cytokine production in ex vivo lamina propria/mesenteric lymphocytes, a macrophage cell line, and the mixed lymphocyte reaction. An optimal regimen against colitis was explored. The contents of MSC-CM were analyzed using a WNT signaling pathway polymerase chain reaction array, an inflammatory cytokines antibody array, and liquid chromatography-tandem mass spectrometry analysis.

RESULTS

Independent of the systemic administration route, MSC-CM concentrates were effective for the inductive phase of TNBS-induced colitis and for the recovery phase of DSS-induced colitis. Hypoxia appeared to be one of the optimal preconditioning factors assessed by cell motility and viability through activating the PI3K-Akt pathway in rat small intestine epithelial cells, IEC-6. Thus, Hypoxia had profound effects on the contents of MSC-CM, which comprised pleiotropic gut trophic factors involved in each wound healing process, including the anti-inflammatory, proliferative, and tissue remodeling phases.

CONCLUSIONS

Identification and optimization of potential gut trophic factors in MSC-CM is urgently needed to form the basis for new drug discovery and for optimizing cell-based therapies for inflammatory bowel disease.

Activation of the epidermal growth factor receptor in macrophages regulates cytokine production and experimental colitis

Macrophages regulate innate immunity to maintain intestinal homeostasis and play pathological roles in intestinal inflammation. Activation of the epidermal growth factor receptor (EGFR) promotes cellular proliferation, differentiation, survival, and wound closure in several cell types. However, the impact of EGFR in macrophages remains unclear. This study was to investigate whether EGFR activation in macrophages regulates cytokine production and intestinal inflammation. We found that EGFR was activated in colonic macrophages in mice with dextran sulfate sodium (DSS)-induced colitis and in patients with ulcerative colitis. DSS-induced acute colitis was ameliorated, and recovery from colitis was promoted in Egfr(fl/fl)LysM-Cre mice with myeloid cell-specific deletion of EGFR, compared with LysM-Cre mice. DSS treatment increased IL-10 and TNF levels during the acute phase of colitis, and increased IL-10 but reduced TNF levels during the recovery phase in Egfr(fl/fl)LysM-Cre mice. An anti-IL-10 neutralizing Ab abolished these effects of macrophage-specific EGFR deletion on DSS-induced colitis in Egfr(fl/fl)LysM-Cre mice. LPS stimulated EGFR activation and inhibition of EGFR kinase activity enhanced LPS-stimulated NF-κB activation in RAW 264.7 macrophages. Furthermore, induction of IL-10 production by EGFR kinase-blocked RAW 264.7 cells, in response to LPS plus IFN-γ, correlated with decreased TNF production. Thus, although selective deletion of EGFR in macrophages leads to increases in both pro- and anti-inflammatory cytokines in response to inflammatory stimuli, the increase in the IL-10 level plays a role in suppressing proinflammatory cytokine production, resulting in protection of mice from intestinal inflammation. These results reveal an integrated response of macrophages regulated by EGFR in intestinal inflammatory disorders.

New targets for mucosal healing and therapy in inflammatory bowel diseases

Healing of the inflamed mucosa (mucosal healing) is an emerging new goal for therapy and predicts clinical remission and resection-free survival in inflammatory bowel diseases (IBDs). The era of antitumor necrosis factor (TNF) antibody therapy was a remarkable progress in IBD therapy and anti-TNF agents led to mucosal healing in a subgroup of IBD patients; however, many patients do not respond to anti-TNF treatment highlighting the relevance of finding new targets for therapy of IBD. In particular, current studies are addressing the role of other anticytokine agents including antibodies against interleukin (IL)-6R, IL-13, and IL-12/IL-23 as well as new anti-inflammatory concepts (regulatory T cell therapy, Smad7 antisense, Jak inhibition, Toll-like receptor 9 stimulation, worm eggs). In addition, blockade of T-cell homing via the integrins α4β7 and the addressin mucosal vascular addressin cell adhesion molecule 1 (MAdCAM-1) emerges as a promising new approach for IBD therapy. Here, new approaches for achieving mucosal healing are discussed as well as their implications for future therapy of IBD.

Linking obesity with type 2 diabetes: the role of T-bet

Obesity is a major predisposing factor for the development of type 2 diabetes (T2D) and is an escalating public health issue around the world. The transition from obesity to T2D is preceded by the induction of a state of insulin resistance, which occurs in response to genetic factors and environmental influences, such as diet. Recent advances have implicated inflammatory immune cells and cytokines as critical pathogenic mediators of insulin resistance and T2D. In particular proinflammatory T helper (Th)1 cells and M1 macrophages are recruited to adipose tissue in response to high fat diet and directly promote the development of insulin resistance. The function of these two cell types is linked by the actions of the cytokine interferon (IFN)γ and one of its major transcriptional regulators T-bet. Recent studies in animal models of T2D demonstrate that T-bet is critical for the development of insulin resistance in response to high fat diet as T-bet-deficient animals are protected from the development of insulin resistance. These data indicate that T-bet and type 1 immunity may constitute novel sites of therapeutic intervention for the treatment of insulin resistance and T2D, in obese human patients.

TGF-β: guardian of T cell function

A fundamental aspect of the adaptive immune system is the generation and maintenance of a diverse and self-tolerant T cell repertoire. Through its regulation of T cell development, homeostasis, tolerance, and differentiation, the highly evolutionarily conserved cytokine TGF-β critically supports a functional T cell pool. The pleiotropic nature of this regulation is likely due to the elaborate control of TGF-β production and activation in the immune system, and the intricacy of TGF-β signaling pathways. In this review we discuss the current understanding of TGF-β regulation of T cells.

Genome-wide regulatory analysis reveals that T-bet controls Th17 lineage differentiation through direct suppression of IRF4

The complex relationship between Th1 and Th17 cells is incompletely understood. The transcription factor T-bet is best known as the master regulator of Th1 lineage commitment. However, attention is now focused on the repression of alternate T cell subsets mediated by T-bet, particularly the Th17 lineage. It has recently been suggested that pathogenic Th17 cells express T-bet and are dependent on IL-23. However, T-bet has previously been shown to be a negative regulator of Th17 cells. We have taken an unbiased approach to determine the functional impact of T-bet on Th17 lineage commitment. Genome-wide analysis of functional T-bet binding sites provides an improved understanding of the transcriptional regulation mediated by T-bet, and suggests novel mechanisms by which T-bet regulates Th cell differentiation. Specifically, we show that T-bet negatively regulates Th17 lineage commitment via direct repression of the transcription factor IFN regulatory factor-4 (IRF4). An in vivo analysis of the pathogenicity of T-bet-deficient T cells demonstrated that mucosal Th17 responses were augmented in the absence of T-bet, and we have demonstrated that the roles of T-bet in enforcing Th1 responses and suppressing Th17 responses are separable. The interplay of the two key transcription factors T-bet and IRF4 during the determination of T cell fate choice significantly advances our understanding of the mechanisms underlying the development of pathogenic T cells.

Targeting T and B lymphocytes in inflammatory bowel diseases: lessons from clinical trials

Both innate and adaptive immunity play an important role in the pathogenesis of inflammatory bowel diseases (IBDs). There is strong evidence that especially activated T cells initiate and perpetuate inflammation and tissue destruction. The increased numbers of CD4+ T cells in the intestinal wall of IBD patients may be explained by enhanced influx/activation and decreased apoptosis of these cells. Several studies have demonstrated that the gut-homing receptors CCR9 and α4β7 are selectively induced on T cells during their priming in intestinal inflamed sites. Whereas targeting of activated CD4+ T cells by specific antibody strategies or neutralization of key T-cell cytokines such as IL-2 or IFN-γ has not been effective in human IBD, blocking migration of activated leukocytes, e.g. T cells into the inflamed tissue by specific antibodies such as vedolizumab, seems highly effective. Recently it could also been demonstrated that administration of antigen-specific regulatory T cells to patients with refractory Crohn's disease was not only well tolerated but showed promising results. The role of B cells in human IBD is less clear. B-cell depletion has so far only been studied in ulcerative colitis where rituximab (anti-CD20) therapy failed. Therefore, although the therapeutic targeting of 'inflammatory' T and B cells was not successful in IBD, especially T cells remain key players in IBD. Targeting either T-cell migration or the use of regulatory T cells appears as the most promising 'T-cell-directed' therapies in the future.

Th17-cell plasticity in Helicobacter hepaticus-induced intestinal inflammation

Bacterial-induced intestinal inflammation is crucially dependent on interleukin (IL)-23 and is associated with CD4(+) T helper type 1 (Th1) and Th17 responses. However, the relative contributions of these subsets during the induction and resolution of colitis in T-cell-sufficient hosts remain unknown. We report that Helicobacter hepaticus-induced typhlocolitis in specific pathogen-free IL-10(-/-) mice is associated with elevated frequencies and numbers of large intestinal interferon (IFN)-γ(+) and IFN-γ(+)IL-17A(+) CD4(+) T cells. By assessing histone modifications and transcript levels in IFN-γ(+), IFN-γ(+)IL-17A(+), and IL-17A(+) CD4(+) T cells isolated from the inflamed intestine, we show that Th17 cells are predisposed to upregulate the Th1 program and that they express IL-23R but not IL-12R. Using IL-17A fate-reporter mice, we further demonstrate that H. hepaticus infection gives rise to Th17 cells that extinguish IL-17A secretion and turn on IFN-γ within 10 days post bacterial inoculation. Together, our results suggest that bacterial-induced Th17 cells arising in disease-susceptible hosts contribute to intestinal pathology by switching phenotype, transitioning via an IFN-γ(+)IL-17A(+) stage, to become IFN-γ(+) ex-Th17 cells.

Prophylactic systemic P2X7 receptor blockade prevents experimental colitis

BACKGROUND

The P2X7 receptor (P2X7-R) is a non-selective adenosine triphosphate-gated cation channel present in epithelial and immune cells, and involved in inflammatory response. Extracellular nucleotides released in conditions of cell stress or inflammation may function as a danger signal alerting the immune system from inflammation. We investigated the therapeutic action of P2X7-R blockade in a model of inflammatory bowel disease.

METHODS

Rats with trinitrobenzene sulfonic (TNBS) acid-induced colitis were treated with the P2X7-R antagonists A740003 or brilliant blue G (BBG) through intra-peritoneal (IP) or intra-colonic (IC) injection prior to colitis induction. Clinical and endoscopic follow-up, histological scores, myeloperoxidase activity, densities of collagen fibers and goblet cells were evaluated. P2X7-R expression, NF-kappa B and Erk activities, and densities of T-cells and macrophages were analyzed by immunoperoxidase. The inflammatory response was determined by measuring inflammatory cytokines in cultures of colon explants, by enzyme-linked immunosorbent assay. Colonic apoptosis was determined by the TUNEL assay.

RESULTS

IP-BBG significantly attenuated the severity of colitis, myeloperoxidase activity, collagen deposition, densities of lamina propria T-cells and macrophages, while maintaining goblet cell densities. IP-BBG inhibited the increase in P2X7-R expression in parallel with apoptotic rates. TNF-α and interleukin-1β stabilized in low levels, while TGF-β and interleukin-10 did not change following IP-BBG-therapy. Colonic NF-kappa-B and Erk activation were significantly lower in IP-BBG-treated animals. Prophylactic IP-A740003 also protected rats against the development of TNBS-colitis.

CONCLUSIONS

Prophylactic systemic P2X7-R blockade is effective in the prevention of experimental colitis, probably due to a systemic anti-inflammatory action, interfering with a stress-inflammation amplification loop mediated by P2X7-R.