Interaction Between the Microbiota, Epithelia, and Immune Cells in the Intestine.

The gastrointestinal tract harbors numerous commensal bacteria, referred to as the microbiota, that benefit host health by digesting dietary components and eliminating pathogens. The intestinal microbiota maintains epithelial barrier integrity and shapes the mucosal immune system, balancing host defense and oral tolerance with microbial metabolites, components, and attachment to host cells. To avoid aberrant immune responses, epithelial cells segregate the intestinal microbiota from immune cells by constructing chemical and physical barriers, leading to the establishment of host-commensal mutualism. Furthermore, intestinal immune cells participate in the maintenance of a healthy microbiota community and reinforce epithelial barrier functions. Perturbations of the microbiota composition are commonly observed in patients with autoimmune diseases and chronic inflammatory disorders. An understanding of the intimate interactions between the intestinal microbiota, epithelial cells, and immune cells that are crucial for the maintenance of intestinal homeostasis might promote advances in diagnostic and therapeutic approaches for various diseases.

GPR31-dependent dendrite protrusion of intestinal CX3CR1+ cells by bacterial metabolites.

Small intestinal mononuclear cells that express CX3CR1 (CX3CR1+ cells) regulate immune responses1-5. CX3CR1+ cells take up luminal antigens by protruding their dendrites into the lumen1-4,6. However, it remains unclear how dendrite protrusion by CX3CR1+ cells is induced in the intestine. Here we show in mice that the bacterial metabolites pyruvic acid and lactic acid induce dendrite protrusion via GPR31 in CX3CR1+ cells. Mice that lack GPR31, which was highly and selectively expressed in intestinal CX3CR1+ cells, showed defective dendrite protrusions of CX3CR1+ cells in the small intestine. A methanol-soluble fraction of the small intestinal contents of specific-pathogen-free mice, but not germ-free mice, induced dendrite extension of intestinal CX3CR1+ cells in vitro. We purified a GPR31-activating fraction, and identified lactic acid. Both lactic acid and pyruvic acid induced dendrite extension of CX3CR1+ cells of wild-type mice, but not of Gpr31b-/- mice. Oral administration of lactate and pyruvate enhanced dendrite protrusion of CX3CR1+ cells in the small intestine of wild-type mice, but not in that of Gpr31b-/- mice. Furthermore, wild-type mice treated with lactate or pyruvate showed an enhanced immune response and high resistance to intestinal Salmonella infection. These findings demonstrate that lactate and pyruvate, which are produced in the intestinal lumen in a bacteria-dependent manner, contribute to enhanced immune responses by inducing GPR31-mediated dendrite protrusion of intestinal CX3CR1+ cells.

Differential dependence on microbiota of IL-23/IL-22-dependent gene expression between the small- and large-intestinal epithelia.

In the intestine, interleukin (IL)-23 and IL-22 from immune cells in the lamina propria contribute to maintenance of the gut epithelial barrier through the induction of antimicrobial production and the promotion of epithelial cell proliferation. Several previous studies suggested that some of the functions of the IL-23/IL-22 axis on intestinal epithelial cells are shared between the small and large intestines. However, the similarities and differences of the IL-23/IL-22 axis on epithelial cells between these two anatomical sites remain unclear. Here, we comprehensively analyzed the gene expression of intestinal epithelial cells in the ileum and colon of germ-free, Il23-/- , and Il22-/- mice by RNA-sequencing. We found that while the IL-23/IL-22 axis is largely dependent on gut microbiota in the small intestine, it is much less dependent on it in the large intestine. In addition, the negative regulation of lipid metabolism in the epithelial cells by IL-23 and IL-22 in the small intestine was revealed, whereas the positive regulation of epithelial cell proliferation by IL-23 and IL-22 in the large intestine was highlighted. These findings shed light on the intestinal site-specific role of the IL-23/IL-22 axis in maintaining the physiological functions of intestinal epithelial cells.

The ectoenzyme E-NPP3 negatively regulates ATP-dependent chronic allergic responses by basophils and mast cells.

Crosslinking of the immunoglobulin receptor FcεRI activates basophils and mast cells to induce immediate and chronic allergic inflammation. However, it remains unclear how the chronic allergic inflammation is regulated. Here, we showed that ecto-nucleotide pyrophosphatase-phosphodiesterase 3 (E-NPP3), also known as CD203c, rapidly induced by FcεRI crosslinking, negatively regulated chronic allergic inflammation. Basophil and mast cell numbers increased in Enpp3(-/-) mice with augmented serum ATP concentrations. Enpp3(-/-) mice were highly sensitive to chronic allergic pathologies, which was reduced by ATP blockade. FcεRI crosslinking induced ATP secretion from basophils and mast cells, and ATP activated both cells. ATP clearance was impaired in Enpp3(-/-) cells. Enpp3(-/-)P2rx7(-/-) mice showed decreased responses to FcεRI crosslinking. Thus, ATP released by FcεRI crosslinking stimulates basophils and mast cells for further activation causing allergic inflammation. E-NPP3 decreases ATP concentration and suppresses basophil and mast cell activity.

The ATP-hydrolyzing ectoenzyme E-NTPD8 attenuates colitis through modulation of P2X4 receptor-dependent metabolism in myeloid cells.

Extracellular adenosine triphosphate (ATP) released by mucosal immune cells and by microbiota in the intestinal lumen elicits diverse immune responses that mediate the intestinal homeostasis via P2 purinergic receptors, while overactivation of ATP signaling leads to mucosal immune system disruption, which leads to pathogenesis of intestinal inflammation. In the small intestine, hydrolysis of luminal ATP by ectonucleoside triphosphate diphosphohydrolase (E-NTPD)7 in epithelial cells is essential for control of the number of T helper 17 (Th17) cells. However, the molecular mechanism by which microbiota-derived ATP in the colon is regulated remains poorly understood. Here, we show that E-NTPD8 is highly expressed in large-intestinal epithelial cells and hydrolyzes microbiota-derived luminal ATP. Compared with wild-type mice, Entpd8-/- mice develop more severe dextran sodium sulfate-induced colitis, which can be ameliorated by either the depletion of neutrophils and monocytes by injecting with anti-Gr-1 antibody or the introduction of P2rx4 deficiency into hematopoietic cells. An increased level of luminal ATP in the colon of Entpd8-/- mice promotes glycolysis in neutrophils through P2x4 receptor-dependent Ca2+ influx, which is linked to prolonged survival and elevated reactive oxygen species production in these cells. Thus, E-NTPD8 limits intestinal inflammation by controlling metabolic alteration toward glycolysis via the P2X4 receptor in myeloid cells.

TRAF6 signaling in dendritic cells plays protective role against infectious colitis by limiting C. rodentium infection through the induction of Th1 and Th17 responses.

Tumor necrosis factor receptor-associated factor 6 (TRAF6) plays a pivotal role in the induction of inflammatory responses not only in innate immune cells but also in non-immune cells, leading to the activation of adaptive immunity. Signal transduction mediated by TRAF6, along with its upstream molecule MyD88 in intestinal epithelial cells (IECs) is crucial for the maintenance of mucosal homeostasis following inflammatory insult. The IEC-specific TRAF6-deficient (TRAF6ΔIEC) and MyD88-deficient (MyD88ΔIEC) mice exhibit increased susceptibility to DSS-induced colitis, emphasizing the critical role of this pathway. Moreover, MyD88 also plays a protective role in Citrobacter rodentium (C. rodentium) infection-induced colitis. However, its pathological role of TRAF6 in infectious colitis remains unclear. To investigate the site-specific roles of TRAF6 in response to enteric bacterial pathogens, we infected TRAF6ΔIEC and dendritic cell (DC)-specific TRAF6-deficient (TRAF6ΔDC) mice with C. rodentium and found that the pathology of infectious colitis was exacerbated with significantly decreased survival rates in TRAF6ΔDC mice, but not in TRAF6ΔIEC mice, compared to those in control mice. TRAF6ΔDC mice showed increased bacterial burdens, marked disruption of epithelial and mucosal structures with increased infiltration of neutrophils and macrophages, and elevated cytokine levels in the colon at the late stages of infection. The frequencies of IFN-γ producing Th1 cells and IL-17A producing Th17 cells in the colonic lamina propria were significantly reduced in TRAF6ΔDC mice. Finally, we demonstrated that TRAF6-deficient DCs failed to produce IL-12 and IL-23 in response to C. rodentium stimulation, and to induce both Th1 and Th17 cells in vitro. Thus, TRAF6 signaling in DCs, but not in IECs, protects against colitis induced by C. rodentium infection by producing IL-12 and IL-23 that induce Th1 and Th17 responses in the gut.

An oral WT1 protein vaccine composed of WT1-anchored, genetically engineered Bifidobacterium longum allows for intestinal immunity in mice with acute myeloid leukemia.

Wilms' tumor 1 (WT1) is a promising tumor-associated antigen for cancer immunotherapy. We developed an oral protein vaccine platform composed of WT1-anchored, genetically engineered Bifidobacterium longum (B. longum) and conducted an in vivo study in mice to examine its anticancer activity. Mice were orally treated with phosphate-buffered saline, wild-type B. longum105-A, B. longum 2012 displaying only galacto-N-biose/lacto-N-biose I-binding protein (GLBP), and WT1 protein- and GLBP-expressing B. longum 420. Tumor size reduced significantly in the B. longum 420 group than in the B. longum 105-A and 2012 groups (P < 0.00 l each), indicating B. longum 420's antitumor activity via WT1-specific immune responses. CD8+ T cells played a major role in the antitumor activity of B. longum 420. The proportion of CD103+CD11b+CD11c+ dendritic cells (DCs) increased in the Peyer's patches (PPs) from mice in the B. longum 420 group, indicating the definite activation of DCs. In the PPs, the number and proportion of CD8+ T cells capable of producing interferon-gamma were significantly greater in the B. longum 420 group than in the B. longum 2012 group (P < 0.05 or < 0.01). The production of WT1-specific IgG antibody was significantly higher in the B. longum 420 group than in the 2012 group (P < 0.05). The B. longum 420 group showed the most intense intratumoral infiltration of CD4+ and CD8+ T cells primed by activated DCs in the PPs of mice in the B. longum 420 group. Our findings provide insights into a novel, intestinal bacterium-based, cancer immunotherapy through intestinal immunity.

Epithelial miR-215 negatively modulates Th17-dominant inflammation by inhibiting CXCL12 production in the small intestine.

MicroRNAs are a class of non-coding short-chained RNAs that control cellular functions by downregulating their target genes. Recent research indicates that microRNAs play a role in the maintenance of gut homeostasis. miR-215 was found to be highly expressed in epithelial cells of the small intestine; however, the involvement of miR-215 in gut immunity remains unknown. Here, we show that miR-215 negatively regulates inflammation in the small intestine by inhibiting CXCL12 production. Mice lacking miR-215 showed high susceptibility to inflammation induced by indomethacin, accompanied by an increased number of Th17 cells in the lamina propria of the small intestine. Our findings provide a rationale for targeting miR-215 as a therapeutic intervention for inflammatory conditions in the small intestine.

Genomic repertoires linked with pathogenic potency of arthritogenic Prevotella copri isolated from the gut of patients with rheumatoid arthritis.

OBJECTIVES: Prevotella copri is considered to be a contributing factor in rheumatoid arthritis (RA). However, in some non-Westernised countries, healthy individuals also harbour an abundance of P. copri in the intestine. This study investigated the pathogenicity of RA patient-derived P. copri (P. copri RA) compared with healthy control-derived P. copri (P. copri HC). METHODS: We obtained 13 P. copri strains from the faeces of patients with RA and healthy controls. Following whole genome sequencing, the sequences of P. copri RA and P. copri HC were compared. To analyse the arthritis-inducing ability of P. copri, we examined two arthritis models (1) a collagen-induced arthritis model harbouring P. copri under specific-pathogen-free conditions and (2) an SKG mouse arthritis model under P. copri-monocolonised conditions. Finally, to evaluate the ability of P. copri to activate innate immune cells, we performed in vitro stimulation of bone marrow-derived dendritic cells (BMDCs) by P. copri RA and P. copri HC. RESULTS: Comparative genomic analysis revealed no apparent differences in the core gene contents between P. copri RA and P. copri HC, but pangenome analysis revealed the high genome plasticity of P. copri. We identified a P. copri RA-specific genomic region as a conjugative transposon. In both arthritis models, P. copri RA-induced more severe arthritis than P. copri HC. In vitro BMDC stimulation experiments revealed the upregulation of IL-17 and Th17-related cytokines (IL-6, IL-23) by P. copri RA. CONCLUSION: Our findings reveal the genetic diversity of P. copri, and the genomic signatures associated with strong arthritis-inducing ability of P. copri RA. Our study contributes towards elucidation of the complex pathogenesis of RA.

Pyruvate enhances oral tolerance via GPR31.

CX3CR1high myeloid cells in the small intestine mediate the induction of oral tolerance by driving regulatory T (Treg) cells. Bacterial metabolites, e.g. pyruvate and lactate, induce a dendrite extension of CX3CR1high myeloid cells into the intestinal lumen via GPR31. However, it remains unclear whether the pyruvate-GPR31 axis is involved in the induction of oral tolerance. Here, we show that pyruvate enhances oral tolerance in a GPR31-dependent manner. In ovalbumin (OVA)-fed Gpr31-deficient mice, an OVA-induced delayed-type hypersensitivity response was substantially induced, demonstrating the defective induction of oral tolerance in Gpr31-deficient mice. The percentage of RORγt+ Treg cells in the small intestine was reduced in Gpr31-deficient mice. In pyruvate-treated wild-type mice, a low dose of OVA efficiently induced oral tolerance. IL-10 production from intestinal CX3CR1high myeloid cells was increased by OVA ingestion in wild-type mice, but not in Gpr31-deficient mice. CX3CR1high myeloid cell-specific IL-10-deficient mice showed a defective induction of oral tolerance to OVA and a decreased accumulation of OVA-specific Treg cells in the small intestine. These findings demonstrate that pyruvate enhances oral tolerance through a GPR31-dependent effect on intestinal CX3CR1high myeloid cells.

Protease inhibitory activity of secretory leukocyte protease inhibitor ameliorates murine experimental colitis by protecting the intestinal epithelial barrier.

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder in the intestine, and the dysfunction of intestinal epithelial barrier (IEB) may trigger the onset of IBD. Secretory leukocyte protease inhibitor (SLPI) is a serine protease inhibitor that has been implicated in the tissue-protective effect in the skin and lung. We found that SLPI was induced in lipopolysaccharides-treated colon carcinoma cell line and in the colon of dextran sulfate sodium (DSS)-treated mice. SLPI-deficient mice were administered DSS to induce colitis and sustained severe inflammation compared with wild-type mice. The colonic mucosa of SLPI-deficient mice showed more severe inflammation with neutrophil infiltration and higher levels of proinflammatory cytokines compared with control mice. Moreover, neutrophil elastase (NE) activity in SLPI-deficient mice was increased and IEB function was severely impaired in the colon, accompanied with the increased number of apoptotic cells. Importantly, we demonstrated that DSS-induced colitis was ameliorated by administration of protease inhibitor SSR69071 and recombinant SLPI. These results suggest that the protease inhibitory activity of SLPI protects from colitis by preventing IEB dysfunction caused by excessive NE activity, which provides insight into the novel function of SLPI in the regulation of gut homeostasis and therapeutic approaches for IBD.

Alleviation of colonic inflammation by Lypd8 in a mouse model of inflammatory bowel disease.

Dysfunction of the intestinal mucosal barrier causes inflammatory bowel diseases (IBDs). Indeed, mucosal barrier impairment in the gut of IBD patients results from decreased expression of barrier molecules. Ly6/Plaur domain containing 8 (Lypd8) segregates microbiota from the colonic epithelial layer. In this study, we found that Lypd8-/- mice, in which flagellated bacteria invaded the mucosal surface of the colon, developed spontaneous colitis when dysbiosis was induced by a high-fat diet (HFD). On the basis of this finding, we assessed whether the application of human LYPD8 (hLYPD8) protein exhibiting the glycan-dependent inhibition of bacterial motility is effective in a colitis model. Oral and anal treatments with hLYPD8 protein ameliorate dextran sulfate sodium-induced colitis and HFD-induced colitis in Lypd8-/- mice. These results indicate a therapeutic potential of hLYPD8 protein supplementation for IBD.

Lypd8 promotes the segregation of flagellated microbiota and colonic epithelia.

Colonic epithelial cells are covered by thick inner and outer mucus layers. The inner mucus layer is free of commensal microbiota, which contributes to the maintenance of gut homeostasis. In the small intestine, molecules critical for prevention of bacterial invasion into epithelia such as Paneth-cell-derived anti-microbial peptides and regenerating islet-derived 3 (RegIII) family proteins have been identified. Although there are mucus layers providing physical barriers against the large number of microbiota present in the large intestine, the mechanisms that separate bacteria and colonic epithelia are not fully elucidated. Here we show that Ly6/PLAUR domain containing 8 (Lypd8) protein prevents flagellated microbiota invading the colonic epithelia in mice. Lypd8, selectively expressed in epithelial cells at the uppermost layer of the large intestinal gland, was secreted into the lumen and bound flagellated bacteria including Proteus mirabilis. In the absence of Lypd8, bacteria were present in the inner mucus layer and many flagellated bacteria invaded epithelia. Lypd8(-/-) mice were highly sensitive to intestinal inflammation induced by dextran sulfate sodium (DSS). Antibiotic elimination of Gram-negative flagellated bacteria restored the bacterial-free state of the inner mucus layer and ameliorated DSS-induced intestinal inflammation in Lypd8(-/-) mice. Lypd8 bound to flagella and suppressed motility of flagellated bacteria. Thus, Lypd8 mediates segregation of intestinal bacteria and epithelial cells in the colon to preserve intestinal homeostasis.

Fecal Stream Diversion Changes Intestinal Environment, Modulates Mucosal Barrier, and Attenuates Inflammatory Cells in Crohn's Disease.

BACKGROUND: The intestinal environment plays important roles in mucosal barrier homeostasis and intestinal inflammation, as clarified in studies using experimental animals but not in humans. AIMS: We investigated whether environmental changes in the fecal stream cause phenotypic changes in the human mucosal barrier. METHODS: We obtained human ileal samples after fecal stream diversions in patients with rectal cancer or Crohn's disease. We investigated the bacterial load and diversity in the human defunctioned ileum, defined as the anal side of the ileum relative to the ileostomy. We also examined the epithelium and lamina propria cell phenotypes in the defunctioned ileum. RESULTS: After fecal stream diversion, bacterial loads decreased significantly in the defunctioned ileum. Based on the Chao1, Shannon, and observed species indices, the diversity of mucosa-associated microbiota was lower in the defunctioned ileum than in the functional ileum. Moreover, the healthy defunctioned ileum showed reductions in villous height, goblet cell numbers, and Ki-67+ cell numbers. Additionally, interferon-γ+, interleukin-17+, and immunoglobulin A+ cell abundance in the lamina propria decreased. After the intestinal environment was restored with an ileostomy closure, the impaired ileal homeostasis recovered. The defunctioned ileum samples from patients with Crohn's disease also showed reductions in interferon-γ+ and interleukin-17+ cell numbers. CONCLUSIONS: Fecal stream diversion reduced the abundance and diversity of intestinal bacteria. It also altered the intestinal mucosal barrier, similar to the alterations observed in germ-free animals. In patients with Crohn's disease, Th1 and Th17 cell numbers were attenuated, which suggests that the host-microbiome interaction is important in disease pathogenesis.

Oral intake of silica nanoparticles exacerbates intestinal inflammation.

Nanoparticles, i.e., particles with a diameter of ≤100 nm regardless of their composing material, are added to various foods as moisturizers, coloring agents, and preservatives. Silicon dioxide (SiO2, silica) nanoparticles in particular are widely used as food additives. However, the influence of SiO2 nanoparticle oral consumption on intestinal homeostasis remains unclear. The daily intake of 10-nm-sized SiO2 nanoparticles exacerbates dextran sulfate sodium (DSS)-induced colitis, whereas the daily intake of 30-nm-sized SiO2 nanoparticles has no influence on intestinal inflammation. The exacerbation of colitis induced by consuming 10-nm-sized SiO2 nanoparticles was abolished in mice deficient in apoptosis-associated speck-like protein containing a CARD (ASC). Our study indicates that the oral intake of small SiO2 nanoparticles poses a risk for worsening intestinal inflammation through activation of the ASC inflammasome.

Heme ameliorates dextran sodium sulfate-induced colitis through providing intestinal macrophages with noninflammatory profiles.

The local environment is crucial for shaping the identities of tissue-resident macrophages (Mϕs). When hemorrhage occurs in damaged tissues, hemoglobin induces differentiation of anti-inflammatory Mϕs with reparative function. Mucosal bleeding is one of the pathological features of inflammatory bowel diseases. However, the heme-mediated mechanism modulating activation of intestinal innate immune cells remains poorly understood. Here, we show that heme regulates gut homeostasis through induction of Spi-C in intestinal CX3CR1high Mϕs. Intestinal CX3CR1high Mϕs highly expressed Spi-C in a heme-dependent manner, and myeloid lineage-specific Spic-deficient (Lyz2-cre; Spicflox/flox ) mice showed severe intestinal inflammation with an increased number of Th17 cells during dextran sodium sulfate-induced colitis. Spi-C down-regulated the expression of a subset of Toll-like receptor (TLR)-inducible genes in intestinal CX3CR1high Mϕs to prevent colitis. LPS-induced production of IL-6 and IL-1α, but not IL-10 and TNF-α, by large intestinal Mϕs from Lyz2-cre; Spicflox/flox mice was markedly enhanced. The interaction of Spi-C with IRF5 was linked to disruption of the IRF5-NF-κB p65 complex formation, thereby abrogating recruitment of IRF5 and NF-κB p65 to the Il6 and Il1a promoters. Collectively, these results demonstrate that heme-mediated Spi-C is a key molecule for the noninflammatory signature of intestinal Mϕs by suppressing the induction of a subset of TLR-inducible genes through binding to IRF5.

BATF2 prevents T-cell-mediated intestinal inflammation through regulation of the IL-23/IL-17 pathway.

Inappropriate activation of the IL-23 signaling pathway causes chronic inflammation through the induction of immunopathological Th17 cells in several tissues including the intestine, whereas adequate Th17 responses are essential for host defense against harmful organisms. In the intestinal lamina propria, IL-23 is primarily produced by innate myeloid cells including dendritic cells (DCs) and macrophages (Mϕs). However, the molecular mechanisms underlying the regulation of IL-23 production by these cells remains poorly understood. In this study, we demonstrated that BATF2 regulates intestinal homeostasis by inhibiting IL-23-driven T-cell responses. Batf2 was highly expressed in intestinal innate myeloid subsets, such as monocytes, CD11b+ CD64+ Mϕs and CD103+ DCs. Batf2-/- mice spontaneously developed colitis and ileitis with altered microbiota composition. In this context, IL-23, but not TNF-α and IL-10, was produced in high quantities by intestinal CD11b+ CD64+ Mϕs from Batf2-/- mice compared with wild-type mice. Moreover, increased numbers of IFN-γ+, IL-17+ and IFN-γ+ IL-17+ CD4+ T cells, but not IL-10+ CD4+ T cells, accumulated in the colons and small intestines of Batf2-/- mice. In addition, RORγt-expressing innate lymphoid cells were increased in Batf2-/- mice. Batf2-/-Rag2-/- mice showed a reduction in intestinal inflammation present in Batf2-/- mice. Furthermore, the high numbers of intestinal IL-17+ and IFN-γ+ IL-17+ CD4+ T cells were markedly reduced in Batf2-/- mice when introducing Il23a deficiency, which was associated with the abrogation of intestinal inflammation. These results indicated that BATF2 in innate myeloid cells is a key molecule for the suppression of IL-23/IL-17 pathway-mediated adaptive intestinal pathology.

Non-Ischemic Heart Failure With Reduced Ejection Fraction Is Associated With Altered Intestinal Microbiota.

BACKGROUND: Research suggests that heart failure with reduced ejection fraction (HFrEF) is a state of systemic inflammation that may be triggered by microbial products passing into the bloodstream through a compromised intestinal barrier. However, whether the intestinal microbiota exhibits dysbiosis in HFrEF patients is largely unknown.Methods and Results:Twenty eight non-ischemic HFrEF patients and 19 healthy controls were assessed by 16S rRNA analysis of bacterial DNA extracted from stool samples. After processing of sequencing data, bacteria were taxonomically classified, diversity indices were used to examine microbial ecology, and relative abundances of common core genera were compared between groups. Furthermore, we predicted gene carriage for bacterial metabolic pathways and inferred microbial interaction networks on multiple taxonomic levels.Bacterial communities of both groups were dominated by the Firmicutes and Bacteroidetes phyla. The most abundant genus in both groups wasBacteroides. Although α diversity did not differ between groups, ordination by ß diversity metrics revealed a separation of the groups across components of variation.StreptococcusandVeillonellawere enriched in the common core microbiota of patients, whileSMB53was depleted. Gene families in amino acid, carbohydrate, vitamin, and xenobiotic metabolism showed significant differences between groups. Interaction networks revealed a higher degree of correlations between bacteria in patients. CONCLUSIONS: Non-ischemic HFrEF patients exhibited multidimensional differences in intestinal microbial communities compared with healthy subjects.

Maintenance of gut homeostasis by the mucosal immune system.

Inflammatory bowel diseases (IBD) are represented by ulcerative colitis (UC) and Crohn's disease (CD), both of which involve chronic intestinal inflammation. Recent evidence has indicated that gut immunological homeostasis is maintained by the interaction between host immunity and intestinal microbiota. A variety of innate immune cells promote or suppress T cell differentiation and activation in response to intestinal bacteria or their metabolites. Some commensal bacteria species or bacterial metabolites enhance or repress host immunity by inducing T helper (Th) 17 cells or regulatory T cells. Intestinal epithelial cells between host immune cells and intestinal microbiota contribute to the separation of these populations and modulate host immune responses to intestinal microbiota. Therefore, the imbalance between host immunity and intestinal microbiota caused by host genetic predisposition or abnormal environmental factors promote susceptibility to intestinal inflammation.

Ecto-nucleoside triphosphate diphosphohydrolase 7 controls Th17 cell responses through regulation of luminal ATP in the small intestine.

Extracellular ATP is released from live cells in controlled conditions, as well as dying cells in inflammatory conditions, and, thereby, regulates T cell responses, including Th17 cell induction. The level of extracellular ATP is closely regulated by ATP hydrolyzing enzymes, such as ecto-nucleoside triphosphate diphosphohydrolases (ENTPDases). ENTPDase1/CD39, which is expressed in immune cells, was shown to regulate immune responses by downregulating the ATP level. In this study, we analyzed the immunomodulatory function of ENTPDase7, which is preferentially expressed in epithelial cells in the small intestine. The targeted deletion of Entpd7 encoding ENTPDase7 in mice resulted in increased ATP levels in the small intestinal lumen. The number of Th17 cells was selectively increased in the small intestinal lamina propria in Entpd7(-/-) mice. Th17 cells were decreased by oral administration of antibiotics or the ATP antagonist in Entpd7(-/-) mice, indicating that commensal microbiota-dependent ATP release mediates the enhanced Th17 cell development in the small intestinal lamina propria of Entpd7(-/-) mice. In accordance with the increased number of small intestinal Th17 cells, Entpd7(-/-) mice were resistant to oral infection with Citrobacter rodentium. Entpd7(-/-) mice suffered from severe experimental autoimmune encephalomyelitis, which was associated with increased numbers of CD4(+) T cells producing both IL-17 and IFN-γ. Taken together, these findings demonstrate that ENTPDase7 controls the luminal ATP level and, thereby, regulates Th17 cell development in the small intestine.