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The transcription factor c-MAF is required for the generation of Helicobacter -specific regulatory T cells that selectively restrain pro-inflammatory T H 17 cells; the absence of c-MAF in mouse regulatory T cells results in pathobiont-dependent inflammatory bowel disease. Tolerance mechanism against a gut commensal pathobiont Some common commensal gut bacteria that can cause spontaneous colitis—chronic inflammation in the colon—in susceptible individuals are well tolerated in others, but the reason for this difference is unclear. In this paper, the authors show that, in mice, the transcription factor c-MAF is required for the generation of Helicobacter -specific regulatory T (T reg ) cells, which selectively retrain Helicobacter -specific pro-inflammatory T helper 17 (T H 17) cells. In the absence of c-MAF or the c-MAF-induced cytokine IL-10, the bacterial-specific T reg –T H 17 balance becomes impaired, and the animals develop pathobiont-dependent inflammatory bowel disease. The authors suggest that engineering non-pathogenic T reg -cell-inducing microbes that express pathobiont antigens could be a therapeutic approach to re-establishing homeostatic conditions in patients with inflammatory bowel disease, reducing the effects of the disease. Both microbial and host genetic factors contribute to the pathogenesis of autoimmune diseases 1 , 2 , 3 , 4 . There is accumulating evidence that microbial species that potentiate chronic inflammation, as in inflammatory bowel disease, often also colonize healthy individuals. These microorganisms, including the Helicobacter species, can induce pathogenic T cells and are collectively referred to as pathobionts 4 , 5 , 6 . However, how such T cells are constrained in healthy individuals is not yet understood. Here we report that host tolerance to a potentially pathogenic bacterium, Helicobacter hepaticus , is mediated by the induction of RORγt + FOXP3 + regulatory T (iT reg ) cells that selectively restrain pro-inflammatory T helper 17 (T H 17) cells and whose function is dependent on the transcription factor c-MAF. Whereas colonization of wild-type mice by H. hepaticus promoted differentiation of RORγt-expressing microorganism-specific iT reg cells in the large intestine, in disease-susceptible IL-10-deficient mice, there was instead expansion of colitogenic T H 17 cells. Inactivation of c-MAF in the T reg cell compartment impaired differentiation and function, including IL-10 production, of bacteria-specific iT reg cells, and resulted in the accumulation of H. hepaticus -specific inflammatory T H 17 cells and spontaneous colitis. By contrast, RORγt inactivation in T reg cells had only a minor effect on the bacteria-specific T reg and T H 17 cell balance, and did not result in inflammation. Our results suggest that pathobiont-dependent inflammatory bowel disease is driven by microbiota-reactive T cells that have escaped this c-MAF-dependent mechanism of iT reg –T H 17 homeostasis.

Host-pathogen interaction influences many non-infectious diseases, including metabolic diseases. Helicobacter hepaticus ( H. hepaticus ) has been found in some metabolic dysfunction-associated steatotic liver disease (MASLD) patients, however, the causal link and underlying mechanisms remain unclear. Here we report that H. hepaticus infection or overexpression of CdtB of H. hepaticus induces lipid deposition in hepatocytes, both in vivo and in vitro. Furthermore, we identify that CdtB translocates to mitochondria with the help of Hsp90, interacts with ATP5A1, reduces mitochondrial respiratory complex V activity, damages mitochondria, and disrupts lipid metabolism. Mechanistically, CdtB-induced lipogenesis depends on the CdtB-mitochondrial ROS-mTORC1-SREBP1 axis and CdtB-mediated NONO expression to enhance nuclear localization of SREBP1 that promote the de novo fatty acid synthesis in the hepatocytes. Neutralization of CdtB significantly alleviates hepatic lipidosis in mice upon H. hepaticus infection. Furthermore, the nucleic acid of H. hepaticus has been detected in the liver tissues of some patients with MASLD, which suggests a certain correlation between liver infection with H. hepaticus and the occurrence and progression of MASLD. Our findings highlight the critical role of CdtB in the pathogenesis of H. hepaticus infection-induced hepatic lipidosis and its potential as a therapeutic target. Here, the authors show that hepatic lipid accumulation induced by Helicobacter hepaticus involves mitochondrial dysfunction and disrupted lipid metabolism via CdtB-ROS-mTORC1-SREBP1 and NONO, highlighting CdtB as a key mediator and potential therapeutic target.

Pioneering work in the 1990s first linked a novel microaerobic bacterium, Helicobacter hepaticus, with chronic active hepatitis and inflammatory bowel disease in several murine models. Targeted H. hepaticus infection experiments subsequently demonstrated its ability to induce colitis, colorectal cancer, and extraintestinal diseases in a number of mouse strains with defects in immune function and/or regulation. H. hepaticus is now widely utilized as a model system to dissect how intestinal microbiota interact with the host to produce both inflammatory and tolerogenic responses. This model has been used to make important advances in understanding factors that regulate both acquired and innate immune response within the intestine. Further, it has been an effective tool to help define the function of regulatory T cells, including their ability to directly inhibit the innate inflammatory response to gut microbiota. The complete genomic sequence of H. hepaticus has advanced the identification of several virulence factors and aided in the elucidation of H. hepaticus pathogenesis. Delineating targets of H. hepaticus virulence factors could facilitate novel approaches to treating microbially induced lower bowel inflammatory diseases.

Helicobacter hepaticus -infected Rag 2 ⁻/⁻ mice emulate many aspects of human inflammatory bowel disease, including the development of colitis and colon cancer. To elucidate mechanisms of inflammation-induced carcinogenesis, we undertook a comprehensive analysis of histopathology, molecular damage, and gene expression changes during disease progression in these mice. Infected mice developed severe colitis and hepatitis by 10 wk post-infection, progressing into colon carcinoma by 20 wk post-infection, with pronounced pathology in the cecum and proximal colon marked by infiltration of neutrophils and macrophages. Transcriptional profiling revealed decreased expression of DNA repair and oxidative stress response genes in colon, but not in liver. Mass spectrometric analysis revealed higher levels of DNA and RNA damage products in liver compared to colon and infection-induced increases in 5-chlorocytosine in DNA and RNA and hypoxanthine in DNA. Paradoxically, infection was associated with decreased levels of DNA etheno adducts. Levels of nucleic acid damage from the same chemical class were strongly correlated in both liver and colon. The results support a model of inflammation-mediated carcinogenesis involving infiltration of phagocytes and generation of reactive species that cause local molecular damage leading to cell dysfunction, mutation, and cell death. There are strong correlations among histopathology, phagocyte infiltration, and damage chemistry that suggest a major role for neutrophils in inflammation-associated cancer progression. Further, paradoxical changes in nucleic acid damage were observed in tissue- and chemistry-specific patterns. The results also reveal features of cell stress response that point to microbial pathophysiology and mechanisms of cell senescence as important mechanistic links to cancer.

Mutations in the NOD2 gene are strong genetic risk factors for ileal Crohn's disease. However, the mechanism by which these mutations predispose to intestinal inflammation remains a subject of controversy. We report that Nod2-deficient mice inoculated with Helicobacter hepaticus, an opportunistic pathogenic bacterium, developed granulomatous inflammation of the ileum, characterized by an increased expression of Th1-related genes and inflammatory cytokines. The Peyer's patches and mesenteric lymph nodes were markedly enlarged with expansion of IFN-γ–producing CD4 and CD8 T cells. Rip2-deficient mice exhibited a similar phenotype, suggesting that Nod2 function likely depends on the Rip2 kinase in this model. Transferring wild-type bone marrow cells into irradiated Nod2-deficient mice did not rescue the phenotype. However, restoring crypt antimicrobial function of Nod2-deficient mice by transgenic expression of α-defensin in Paneth cells rescued the Th1 inflammatory phenotype. Therefore, through the regulation of intestinal microbes, Nod2 function in nonhematopoietic cells of the small intestinal crypts is critical for protecting mice from a Th1-driven granulomatous inflammation in the ileum. The model may provide insight into Nod2 function relevant to inflammation of ileal Crohn's disease.

Humans are colonized by multitudes of commensal organisms representing members of five of the six kingdoms of life; however, our gastrointestinal tract provides residence to both beneficial and potentially pathogenic microorganisms. Imbalances in the composition of the bacterial microbiota, known as dysbiosis, are postulated to be a major factor in human disorders such as inflammatory bowel disease. We report here that the prominent human symbiont Bacteroides fragilis protects animals from experimental colitis induced by Helicobacter hepaticus, a commensal bacterium with pathogenic potential. This beneficial activity requires a single microbial molecule (polysaccharide A, PSA). In animals harbouring B. fragilis not expressing PSA, H. hepaticus colonization leads to disease and pro-inflammatory cytokine production in colonic tissues. Purified PSA administered to animals is required to suppress pro-inflammatory interleukin-17 production by intestinal immune cells and also inhibits in vitro reactions in cell cultures. Furthermore, PSA protects from inflammatory disease through a functional requirement for interleukin-10-producing CD4 + T cells. These results show that molecules of the bacterial microbiota can mediate the critical balance between health and disease. Harnessing the immunomodulatory capacity of symbiosis factors such as PSA might potentially provide therapeutics for human inflammatory disorders on the basis of entirely novel biological principles. A gut issue: Bacterial symbiosis shapes a healthy immune response (Nature Cover 29 May 2008) Microbiologists are beginning to understand how and why mammals are colonized by multitudes of symbiotic bacteria. But what differentiates 'good' from benign or harmful bacteria remains largely unknown. The intestinal microbe Bacteroides fragilis was shown in 2005 to have profound effect on the mammalian immune system, an effect ascribed to a single molecule, capsular polysaccharide A (PSA). Now B. fragilis PSA is shown to protect animals against both bacterial and chemical colitis in a process involving interleukin-10-producing T cells. This suggests that B. fragilis helps maintain human health by suppressing the intestinal inflammatory response, and that symbiosis factors may provide a route to new therapies. In the cover graphic (by Tom DiCesere, Sarkis Mazmanian & Dennis Kasper), In the cover graphic, PSA (yellow) surrounds B. fragilis (green) in the intestine and is taken up by a dendritic cell and processed within the endosomal pathway to a reduced molecular size. The depolymerized PSA is presented by the major histocompatibility complex class II molecule to the CD4 + T cell (green, white, yellow), which becomes activated. Work in this field is being promoted by several major efforts to characterize the human microbiota and determine its role in health and disease, including the Human Microbiome Project. In News Features, Asher Mullard examines the various approaches, and Apoorva Mandavilli reports on a rare opportunity to watch the gut being colonized from scratch after intestinal transplants. Bacteroides fragilis is a member of the human intestinal microbiota. It is reported that a single molecule produced by this bacterium, polysaccharide A, can suppress the intestinal inflammatory response and thus protect from experimental colitis.

•Neonatal Hh infection of mice upregulates colonic IL10 message.•Neonatal Hh infection reduces lung immune responses after immunisation with Ad85A.•Protection against Mtb challenge induced by Ad85A is abolished in Hh infected mice.•IL10R blockade reverses the effects of Hh infection on Ad85A induced protection.•Addition of Hh to the microbiota abolishes protection induced by a subunit vaccine. BCG, the only licensed vaccine against tuberculosis (TB), provides geographically variable protection, an effect ascribed to exposure to environmental mycobacteria (EM). Here we show that altering the intestinal microbiota of mice by early-life infection with the commensal bacterium Helicobacter hepaticus (Hh) increases their susceptibility to challenge with Mycobacterium tuberculosis (Mtb). Furthermore Hh-infected mice immunised parenterally with the recombinant subunit vaccine, human adenovirus type 5 expressing the immunodominant antigen 85A of Mtb (Ad85A), display a reduced lung immune response and protection against Mtb challenge is also reduced. Expression of interleukin 10 (IL10) messenger RNA is increased in the colon of Hh infected mice. Treatment of Hh-infected Ad85A-immunised mice with anti-IL10 receptor antibody, following challenge with Mtb, restores the protective effect of the vaccine. These data show for the first time that alteration of the intestinal microbiota by addition of a single commensal organism can profoundly influence protection induced by a TB subunit vaccine via an IL10-dependent mechanism, a result with implications for the deployment of such vaccines in the field.

Summary The enterohepatic Epsilonproteobacterium Helicobacter hepaticus persistently colonizes the intestine of mice and causes chronic inflammatory symptoms in susceptible mouse strains. The bacterial factors causing intestinal inflammation are poorly characterized. A large genomic pathogenicity island, HHGI1, which encodes components of a type VI secretion system (T6SS), was previously shown to contribute to the colitogenic potential of H. hepaticus. We have now characterized the T6SS components Hcp, VgrG1, VgrG2 and VgrG3, encoded on HHGI1, including the potential impact of the T6SS on intestinal inflammation in a mouse T‐cell transfer model. The H. hepaticus T6SS components were expressed during the infection and secreted in a T6SS‐dependent manner, when the bacteria were cultured either in the presence or in the absence of mouse intestinal epithelial cells. Mutants deficient in VgrG1 displayed a significantly lower colitogenic potential in T‐cell‐transferred C57BL/6 Rag2−/− mice, despite an unaltered ability to colonize mice persistently. Intestinal microbiota analyses demonstrated only minor changes in mice infected with wild‐typeH. hepaticus as compared with mice infected with VgrG1‐deficient isogenic bacteria. In addition, competitive assays between both wild‐type and T6SS‐deficient H. hepaticus, and between wild‐type H. hepaticus and Campylobacter jejuni or Enterobacteriaceae species did not show an effect of the T6SS on interbacterial competitiveness. Therefore, we suggest that microbiota alterations did not play a major role in the changes of pro‐inflammatory potential mediated by the T6SS. Cellular innate pro‐inflammatory responses were increased by the secreted T6SS proteins VgrG1 and VgrG2. We therefore concluded that the type VI secretion component VgrG1 can modulate and specifically exacerbate the innate pro‐inflammatory effect of the chronic H. hepaticus infection.

The mouse pathobiont Helicobacter hepaticus can induce typhlocolitis in interleukin-10-deficient mice, and H. hepaticus infection of immunodeficient mice is widely used as a model to study the role of pathogens and commensal bacteria in the pathogenesis of inflammatory bowel disease. C57BL/6J Il10(-/-) mice kept under specific pathogen-free conditions in two different facilities (MHH and MIT), displayed strong differences with respect to their susceptibilities to H. hepaticus-induced intestinal pathology. Mice at MIT developed robust typhlocolitis after infection with H. hepaticus, while mice at MHH developed no significant pathology after infection with the same H. hepaticus strain. We hypothesized that the intestinal microbiota might be responsible for these differences and therefore performed high resolution analysis of the intestinal microbiota composition in uninfected mice from the two facilities by deep sequencing of partial 16S rRNA amplicons. The microbiota composition differed markedly between mice from both facilities. Significant differences were also detected between two groups of MHH mice born in different years. Of the 119 operational taxonomic units (OTUs) that occurred in at least half the cecum or colon samples of at least one mouse group, 24 were only found in MIT mice, and another 13 OTUs could only be found in MHH samples. While most of the MHH-specific OTUs could only be identified to class or family level, the MIT-specific set contained OTUs identified to genus or species level, including the opportunistic pathogen, Bilophila wadsworthia. The susceptibility to H. hepaticus-induced colitis differed considerably between Il10(-/-) mice originating from the two institutions. This was associated with significant differences in microbiota composition, highlighting the importance of characterizing the intestinal microbiome when studying murine models of IBD.

Summary Multiple pathogenic Gram‐negative bacteria produce the cytolethal distending toxin (CDT) with activity of DNase I; CDT can induce DNA double‐strand breaks (DSBs), G2/M cell cycle arrest, and apoptosis in cultured mammalian cells. However, the link of CDT to in vivo tumorigenesis is not fully understood. In this study, 129/SvEv Rag2−/− mice were gavaged with wild‐type Helicobacter hepatics 3B1(Hh) and its isogenic cdtB mutant HhcdtBm7, followed by infection for 10 and 20 weeks (WPI). HhCDT deficiency did not affect cecal colonization levels of HhcdtBm7, but attenuated severity of cecal pathology in HhcdtBm7‐infected mice. Of importance, preneoplasic dysplasia was progressed to cancer from 10 to 20 WPI in the Hh‐infected mice but not in the HhcdtBm7‐infected mice. In addition, the loss of HhCDT significantly dampened transcriptional upregulation of cecal Tnfα and Il‐6, but elevated Il‐10 mRNA levels when compared to Hh at 10 WPI. Furthermore, the presence of HhCDT increased numbers of lower bowel intestinal γH2AX‐positive epithelial cells (a marker of DSBs) at both 10 and 20 WPI and augmented phospho‐Stat3 foci+ intestinal crypts (activation of Stat3) at 20 WPI. Our findings suggest that CDT promoted Hh carcinogenesis by enhancing DSBs and activation of the Tnfα/Il‐6‐Stat3 signaling pathway.