Development of colitis in signal transducers and activators of transcription 6-deficient T-cell receptor alpha-deficient mice: a potential role of signal transducers and activators of transcription 6-independent interleukin-4 signaling for the generation of Th2-biased pathological CD4+ betabetaT cells

Effector T Helper Cell Subsets in Inflammatory Bowel Diseases

The gastrointestinal tract is a site of high immune challenge, as it must maintain a delicate balance between tolerating luminal contents and generating an immune response toward pathogens. CD4⁺ T cells are key in mediating the host protective and homeostatic responses. Yet, CD4⁺ T cells are also known to be the main drivers of inflammatory bowel disease (IBD) when this balance is perturbed. Many subsets of CD4⁺ T cells have been identified as players in perpetuating chronic intestinal inflammation. Over the last few decades, understanding of how each subset of Th cells plays a role has dramatically increased. Simultaneously, this has allowed development of therapeutic innovation targeting specific molecules rather than broad immunosuppressive agents. Here, we review the emerging evidence of how each subset functions in promoting and sustaining the chronic inflammation that characterizes IBD.

Disturbance in the Mucosa-Associated Commensal Bacteria Is Associated with the Exacerbation of Chronic Colitis by Repeated Psychological Stress; Is That the New Target of Probiotics?

Psychological stress can exacerbate inflammatory bowel disease. However, the mechanisms underlying how psychological stress affects gut inflammation remain unclear. Here, we focused on the relationship between changes in the microbial community of mucosa-associated commensal bacteria (MACB) and mucosal immune responses induced by chronic psychological stress in a murine model of ulcerative colitis. Furthermore, we examined the effect of probiotic treatment on exacerbated colitis and MACB composition changes induced by chronic psychological stress. Repeated water avoidance stress (rWAS) in B6-Tcra-/- mice severely exacerbated colitis, which was evaluated by both colorectal tissue weight and histological score of colitis. rWAS treatment increased mRNA expression of UCN2 and IFN-γ in large intestinal lamina propria mononuclear cells (LI-LPMC). Interestingly, exacerbated colitis was associated with changes in the microbial community of MACB, specifically loss of bacterial species diversity and an increase in the component ratio of Clostridium, revealed by 16S rRNA gene amplicon analysis. Finally, the oral administration of a probiotic Lactobacillus strain was protective against the exacerbation of colitis and was associated with a change in the bacterial community of MACB in rWAS-exposed Tcra-/- mice. Taken together, these results suggested that loss of species diversity in MACB might play a key role in exacerbated colitis induced by chronic psychological stress. In addition, probiotic treatment may be used as a tool to preserve the diversity of bacterial species in MACB and alleviate gut inflammation induced by psychological stress.

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.

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.

Establishment of a novel mouse model of ulcerative colitis with concomitant cytomegalovirus infection: in vivo identification of cytomegalovirus persistent infected cells

BACKGROUND

Human cytomegalovirus (HCMV) infection is considered to be an exacerbating factor in patients with ulcerative colitis (UC). However, the pathogenicity of HCMV in the exacerbation of UC remains unclear. The lack of a model mimicking UC with HCMV infection has posed a challenge for research into the pathogenic mechanism of HCMV in flare of UC. Therefore, the aim of our study was to establish a new mouse model of UC with HCMV infection.

METHODS

We established latent murine CMV (MCMV) infection in T-cell receptor α knockout (TCR-α KO) mice at an early age by adjustment of viral dose. Next, we performed immunohistochemical analysis in various organs of infected adult TCR-α KO mice to prove the correlation between MCMV infection and development of colitis. We then assessed colitis histologically and cytokine expression in the colon of infected and uninfected TCR-α KO mice. Finally, the types of MCMV-infected cells in the inflamed colon were examined by immunohistochemical analysis.

RESULTS

MCMV antigen-positive cells reappeared predominantly in the inflamed colon of TCR-α KO mice. Severe colitis developed in the infected TCR-α KO mice compared with uninfected mice, and Th1/Th17 and Th2 responses were strongly induced. MCMV-infected cells were mainly perivascular stromal cells including pericytes, expressing platelet-derived growth factor receptor-beta (PDGFR-β) and CXC chemokine ligand 12 (CXCL12).

CONCLUSIONS

In this study, we established, to our knowledge, the first mouse model of UC with HCMV infection. This model is an excellent tool for clarifying the detailed pathogenicity of HCMV in the exacerbation of UC and developing new treatment strategy for active UC with HCMV infection.

STAT6 deficiency ameliorates severity of oxazolone colitis by decreasing expression of claudin-2 and Th2-inducing cytokines

Patients suffering from ulcerative colitis (UC) exhibit chronic colonic inflammation caused by a dysregulated mucosal immune response and epithelial barrier disruption. Th2 cytokines, including IL-13, have been implicated in the pathogenesis of UC. IL-13 induces phosphorylation of STAT6, and we previously demonstrated increased epithelial p-STAT6 in children with UC. In this study, we investigated the role of STAT6 in oxazolone colitis, a murine model of UC, by inducing colitis in STAT6-deficient (STAT6(-/-)) and wild type (WT) mice. We observed increased epithelial cell, T cell, macrophage, and NKT cell STAT6 phosphorylation, as well as increased p-STAT6(+) IL-13-producing NKT cells, in colitic WT mice. Colitis was attenuated in STAT6(-/-) mice, with improvements in weight, colon length, and histopathology. There was decreased induction of the pore-forming tight junction protein claudin-2 in STAT6(-/-) mice. Similarly, short hairpin RNA STAT6 knockdown reduced claudin-2 induction and transepithelial resistance decrease in IL-13-treated human T84 cells. Tissue expression of IL-13, IFN-γ, IL-17, and IL-10 mRNA was similarly induced in WT and STAT6(-/-) colitic mice; however, we observed increased mRNA expression for the Th2-inducing cytokines IL-33 and thymic stromal lymphopoietin in WT mice with colitis, which was abrogated in STAT6(-/-) mice. Mesenteric lymph node cells from STAT6(-/-) mice with colitis exhibited reduced secretion of IL-4, IL-5, IL-13, and IFN-γ. IL-33 augmented mesenteric lymph node cell secretion of IL-5, IL-13, IL-6, and IFN-γ. These data implicate STAT6 in the pathogenesis of colitis in vivo with important roles in altering epithelial barrier function and regulating Th2-inducing cytokine production.

Mechanisms of intestinal inflammation and development of associated cancers: lessons learned from mouse models

Chronic inflammation is strongly associated with approximately 1/5th of all human cancers. Arising from combinations of factors such as environmental exposures, diet, inherited gene polymorphisms, infections, or from dysfunctions of the immune response, chronic inflammation begins as an attempt of the body to remove injurious stimuli; however, over time, this results in continuous tissue destruction and promotion and maintenance of carcinogenesis. Here we focus on intestinal inflammation and its associated cancers, a group of diseases on the rise and affecting millions of people worldwide. Intestinal inflammation can be widely grouped into inflammatory bowel diseases (ulcerative colitis and Crohn's disease) and celiac disease. Long-standing intestinal inflammation is associated with colorectal cancer and small-bowel adenocarcinoma, as well as extraintestinal manifestations, including lymphomas and autoimmune diseases. This article highlights potential mechanisms of pathogenesis in inflammatory bowel diseases and celiac disease, as well as those involved in the progression to associated cancers, most of which have been identified from studies utilizing mouse models of intestinal inflammation. Mouse models of intestinal inflammation can be widely grouped into chemically induced models; genetic models, which make up the bulk of the studied models; adoptive transfer models; and spontaneous models. Studies in these models have lead to the understanding that persistent antigen exposure in the intestinal lumen, in combination with loss of epithelial barrier function, and dysfunction and dysregulation of the innate and adaptive immune responses lead to chronic intestinal inflammation. Transcriptional changes in this environment leading to cell survival, hyperplasia, promotion of angiogenesis, persistent DNA damage, or insufficient repair of DNA damage due to an excess of proinflammatory mediators are then thought to lead to sustained malignant transformation. With regards to extraintestinal manifestations such as lymphoma, however, more suitable models are required to further investigate the complex and heterogeneous mechanisms that may be at play.

Agonist-driven development of CD4+CD25+Foxp3+ regulatory T cells requires a second signal mediated by Stat6

The factors that induce Foxp3 expression and regulatory T (Treg) cell development remain unknown. In this study, we investigated the role of STAT4 and STAT6 in agonist-driven generation of Ag-specific Foxp3-expressing Treg cells. Our findings indicate that fully efficient induction of Foxp3 expression and development of Ag-specific Treg cells requires the synergistic action of two signals: a TCR-mediated signal and a second signal mediated by STAT6. Indeed, by comparing the development of wild-type and STAT4- and STAT6-deficient hemagglutinin-specific T cells in the presence of hemagglutinin Ag, we found that the absence of STAT6 impaired the generation of Ag-specific CD4+CD25+Foxp3+ cells. Moreover, in transgenic mice expressing a constitutively active form of STAT6, we found that the fraction of CD4+Foxp3+ cells exceeds that of control wild-type littermates. Overall these findings support a role for the STAT6 pathway in Treg cell development and maintenance.

Suppressor of cytokine signaling-1 regulates inflammatory bowel disease in which both IFNgamma and IL-4 are involved

BACKGROUND & AIMS

The suppressor of cytokine signaling-1 (SOCS1) is a potent negative regulator of various cytokines and it has been implicated in the regulation of immune responses. However, the role of SOCS1 in inflammatory bowel diseases (IBDs) has not been clarified. To determine the role of SOCS1 in colitis, we generated SOCS1/T-cell receptor alpha (TCRalpha) double knockout (DKO) mice.

METHODS

The depletion of interferon gamma (IFNgamma) and IL-4 was achieved by crossing the DKO mice with IFNgamma knockout (KO) mice and by the administration of anti-IL-4 antibody, respectively. The activation of cytokine-induced transcription factors was determined by Western blotting with phosphorylation-specific antibodies, and the induction of inflammatory factors was measured by reverse-transcription polymerase chain reaction.

RESULTS

Much more severe colitis developed in 100% of the DKO mice within 9 weeks of age than in TCRalpha-KO mice. Although the proportion and the activation status of CD4(+) TCRalpha(-)beta(+) T cells in DKO mice were similar to those in TCRalpha-KO mice, signal transducer and activator of transcription 1, nuclear factor kappaB, and their target genes were hyperactivated in infiltrated mononuclear cells and colonic epithelial cells in DKO mice. Cytokine-depletion experiments showed that exacerbated colitis in the DKO mice was dependent on both IFNgamma and IL-4. SOCS1-deficient cells were hypersensitive to IFNgamma, IL-4, and lipopolysaccharides, depending on the target genes.

CONCLUSIONS

SOCS1 plays an important role in preventing murine colitis by restricting the cytokine signals. SOCS1/TCRalpha DKO mice could be a useful model for investigating human IBD.

DSS-induced colitis is exacerbated in STAT-6 knockout mice

BACKGROUND

Several transcription factors have been proposed to regulate IBD including the signal transducer and activator of transcription-6 (STAT-6).

METHODS

The role of STAT-6 was examined in the 5% dextran sulfate sodium (DSS)-induced murine model of colitis using STAT-6 and wildtype mice.

RESULTS

The disease activity index (DAI) revealed a significant increase in DAI in STAT-6 mice over STAT-6 mice given DSS. Both STAT-6 and wildtype mice displayed severe inflammation and crypt damage. Additionally, STAT-6 mice showed significant injury to the proximal colon compared with their littermate controls. Furthermore, STAT-6 mice receiving DSS had dramatically higher levels of serum nitrite/nitrate than all other groups. STAT-6 animals also displayed higher levels of inteferon-gamma than wildtype mice.

CONCLUSIONS

Because STAT-6 has been reported to regulate the expression and activity of inducible NO synthase (iNOS), our data suggest that, in DSS colitis, STAT-6 may modulate iNOS, to limit NO formation and control the extent of inflammation in the colon. We conclude that STAT-6 may normally play an important regulatory role in the pathogenesis of inflammatory bowel disease, possibly through modulation of iNOS and interferon-gamma.

Colitis in mice lacking the common cytokine receptor gamma chain is mediated by IL-6-producing CD4+ T cells

BACKGROUND & AIMS

Mice that have a truncated mutation of the common cytokine receptor gamma chain (CR gamma -/Y) are known to spontaneously develop colitis. To identify the pathologic elements responsible for triggering this localized inflammatory disease, we elucidated and characterized aberrant T cells and their enteropathogenic cytokines in CR gamma -/Y mice with colitis.

METHODS

The histologic appearance, cell population, T-cell receptor V beta usage, and cytokine production of lamina propria lymphocytes were assessed. CR gamma -/Y mice were treated with anti-interleukin (IL)-6 receptor monoclonal antibody to evaluate its ability to control colitis, and splenic CD4 + T cells from the same mouse model were adoptively transferred into SCID mice to see if they spurred the appearance of colitis.

RESULTS

We found marked thickening of the large intestine, an increase in crypt depth, and infiltration of the colonic lamina propria and submucosa with mononuclear cells in the euthymic CR gamma -/Y mice, but not in the athymic CR gamma -/Y mice, starting at the age of 8 weeks. Colonic CD4 + T cells with high expressions of antiapoptotic Bcl-x and Bcl-2 were found to use selected subsets (V beta 14) of T-cell receptor and to exclusively produce IL-6. Treatment of CR gamma -/Y mice with anti-IL-6 receptor monoclonal antibody prevented the formation of colitis via the induction of apoptosis in IL-6-producing CD4 + T cells. Adoptive transfer of pathologic CD4 + T cells induced colitis in the recipient SCID mice.

CONCLUSIONS

Colonic IL-6-producing thymus-derived CD4 + T cells are responsible for the development of colitis in CR gamma -/Y mice.

Interleukin-13 augments transforming growth factor-beta1-induced tissue inhibitor of metalloproteinase-1 expression in primary human airway fibroblasts

Tissue inhibitor of metalloproteinase (TIMP)-1 is a potent inhibitor of activated matrix metalloproteinases (MMPs) such as gelatinases and collagenases. TIMP-1 is induced by transforming growth factor-beta1 (TGF-beta1), but details regarding signaling pathways remain unclear. T-helper-2 cytokines also have profibrotic properties and can interact with TGF-beta. In the present study, we examined the effects of interleukin (IL)-13 (2,500 pM) on TGF-beta1 (200 pM)-induced expression of TIMP-1 mRNA and protein in primary human airway fibroblasts obtained from 57 human subjects. IL-13 alone had no effect on TIMP-1 mRNA or protein expression. However, IL-13 synergistically augmented TGF-beta1-induced TIMP-1 mRNA and protein expression (P < 0.001 vs. TGF-beta1 alone). The upregulation of TIMP-1 by the combination of TGF-beta1 and IL-13 involved increased transcription, with little effect on mRNA stabilization. Initial exploration of the pathways leading to the synergy determined that activation of the phosphatidylinositol 3-kinase (PI3K)-Akt pathway by IL-13 may have a negative effect on TIMP-1 production. The specific PI3K inhibitor LY-294002 in the presence of TGF-beta1, IL-13, or the combination of the two caused significant increases in TIMP-1 mRNA expression, while LY-294002 increased TIMP-1 protein levels in the presence of IL-13 alone. These results suggest that IL-13 augments TGF-beta1-induced profibrotic responses at both the mRNA and protein levels. Although IL-13 induced activation of PI3K-Akt, the activation did not contribute to the synergy observed with TGF-beta1 plus IL-13 in TIMP-1 expression and in fact may dampen it. The mechanisms behind the synergy remain to be determined.

Immune networks in animal models of inflammatory bowel disease

The animal models of inflammatory bowel disease provide a framework to define the immunopathogenesis of intestinal inflammation. Studies in these models support the hypothesis that exaggerated immune responses to normal enteric microflora are involved in the initiation and perpetuation of chronic intestinal inflammation. A major pathway involves development of acquired immune responses by the interactions of CD4+ T-cell receptor alphabeta T cells with antigen-presenting cells (dendritic cells). Immunoregulatory cells, including Tr1 cells, Th3 cells, and CD4+ CD25+ T cells and B cells, directly or indirectly affect the T-cell receptor alphabeta T cell-induced immune responses and bridge innate and acquired immunity. The study of these complicated immune networks provides the rationale for the development of new therapeutic interventions in inflammatory bowel disease.