Mycobacterial infection aggravates Helicobacter pylori-induced gastric preneoplastic pathology by redirection of de novo induced Treg cells.

The two human pathogens Helicobacter pylori and Mycobacterium tuberculosis (Mtb) co-exist in many geographical areas of the world. Here, using a co-infection model of H. pylori and the Mtb relative M. bovis bacillus Calmette-Guérin (BCG), we show that both bacteria affect the colonization and immune control of the respective other pathogen. Co-occurring M. bovis boosts gastric Th1 responses and H. pylori control and aggravates gastric immunopathology. H. pylori in the stomach compromises immune control of M. bovis in the liver and spleen. Prior antibiotic H. pylori eradication or M. bovis-specific immunization reverses the effects of H. pylori. Mechanistically, the mutual effects can be attributed to the redirection of regulatory T cells (Treg cells) to sites of M. bovis infection. Reversal of Treg cell redirection by CXCR3 blockade restores M. bovis control. In conclusion, the simultaneous presence of both pathogens exacerbates the problems associated with each individual infection alone and should possibly be factored into treatment decisions

An Antibiotic-Impacted Microbiota Compromises the Development of Colonic Regulatory T Cells and Predisposes to Dysregulated Immune Responses

Antibiotic exposure early in life and other practices impacting the vertical transmission and ordered assembly of a diverse and balanced gut microbiota are associated with a higher risk of immunological and metabolic disorders such as asthma and allergy, autoimmunity, obesity, and susceptibility to opportunistic infections. In this study, we used a model of perinatal exposure to the broad-spectrum antibiotic ampicillin to examine how the acquisition of a dysbiotic microbiota affects neonatal immune system development. We found that the resultant dysbiosis imprints in a manner that is irreversible after weaning, leading to specific and selective alteration of the colonic CD4$^{+}$ T-cell compartment. In contrast, colonic granulocyte and myeloid lineages and other mucosal T-cell compartments are unaffected. Among colonic CD4$^{+}$ T cells, we observed the most pronounced effects on neuropilin-negative, RORγt- and Foxp3-positive regulatory T cells, which are largely absent in antibiotic-exposed mice even as they reach adulthood. Immunomagnetically isolated dendritic cells from antibiotic-exposed mice fail to support the generation of Foxp3$^{+}$ regulatory T cells (Tregs) from naive T cells ex vivo The perinatally acquired dysbiotic microbiota predisposes to dysregulated effector T-cell responses to Citrobacter rodentium or ovalbumin challenge. The transfer of the antibiotic-impacted, but not healthy, fecal microbiota into germfree recipients recapitulates the selective loss of colonic neuropilin-negative, RORγt- and Foxp3-positive Tregs. The combined data indicate that the early-life acquisition of a dysbiotic microbiota has detrimental effects on the diversity and microbial community composition of offspring that persist into adulthood and predisposes to inappropriate T-cell responses that are linked to compromised immune tolerance.IMPORTANCE The assembly of microbial communities that populate all mucosal surfaces of the human body begins right after birth. This process is prone to disruption as newborns and young infants are increasingly exposed to antibiotics, both deliberately for therapeutic purposes, and as a consequence of transmaternal exposure. We show here using a model of ampicillin administration to lactating dams during their newborn offspring's early life that such exposures have consequences that persist into adulthood. Offspring acquire their mother's antibiotic-impacted microbiota, which compromises their ability to generate a colonic pool of CD4$^{+}$ T cells, particularly of colonic regulatory T cells. This Treg deficiency cannot be corrected by cohousing with normal mice later and is recapitulated by reconstitution of germfree mice with microbiota harvested from antibiotic-exposed donors. As a consequence of their dysbiosis, and possibly of their Treg deficiency, antibiotic-impacted offspring generate dysregulated Th1 responses to bacterial challenge infection and develop more severe symptoms of ovalbumin-induced anaphylaxis

BATF3-dependent dendritic cells drive both effector and regulatory T-cell responses in bacterially infected tissues

The gastric lamina propria of mice that have been experimentally infected with the pathobiont Helicobacter pylori hosts a dense network of myeloid cells that includes BATF3-dependent CD103+ dendritic cells (DCs). We show here that CD103+ DCs are strictly required for gastric Th1 responses to H. pylori and for H. pylori infection control. A similar dependence of type 1 immunity on CD103+ DCs is observed in a Mycobacterium bovis BCG infection model, and in a syngeneic colon cancer model. Strikingly, we find that not only the expansion and/or recruitment of Th1 cells, but also of peripherally induced, neuropilin-negative regulatory T-cells to sites of infection requires BATF3-dependent DCs. A shared feature of the examined models is the strongly reduced production of the chemokines and CXCR3 ligands CXCL9, 10 and 11 in BATF3-deficient mice. The results implicate BATF3-dependent DCs in the recruitment of CXCR3+ effector and regulatory T-cells to target tissues and in their local expansion

IRF4 Expression Is Required for the Immunoregulatory Activity of Conventional Type 2 Dendritic Cells in Settings of Chronic Bacterial Infection and Cancer

The lamina propria of the gastrointestinal tract and other mucosal surfaces of humans and mice host a network of mononuclear phagocytes that differ in their ontogeny, surface marker and transcription factor expression, and functional specialization. Conventional dendritic cells (DCs) in particular exist as two major subpopulations in both lymphoid and nonlymphoid organs that can be distinguished based on their surface marker and transcription factor expression. In this study, we show in various Th1- and/or Th17-polarized settings of acute and chronic bacterial infection and of tumor growth that the conditional ablation of Irf4 in CD11c+ DCs results in more efficient immune control of Helicobacter pylori, Mycobacterium bovis bacillus Calmette-Guérin, and Citrobacter rodentium and of tumor growth in a syngeneic tumor model. We attribute the phenotype of IRF4ΔDC mice to unrestricted Th1 responses and in particular to IFN-γ- and TNF-α-expressing CD4+ T cells. This activity of IRF4-expressing DCs is linked to a DC-specific immunoregulatory transcriptional program. In contrast, in Th2-polarized settings such as house dust mite-induced allergic airway inflammation, the lack of IRF4 expression in the DC compartment alleviates inflammation and goblet cell metaplasia. The combined data provide evidence for immunoregulatory properties of this versatile DC population in Th1-polarized infection settings

TGF-β production by eosinophils drives the expansion of peripherally induced neuropilin- RORγt+ regulatory T-cells during bacterial and allergen challenge.

Eosinophils are best known for their effector functions in settings of parasitic infection or allergen challenge, but have also increasingly been implicated in immune regulation at mucosal sites. Here, we show using bacterial infection and antigen challenge models that extrathymic Foxp3(+) regulatory T-cells that arise de novo in the context of bacterial infection require an intact eosinophil compartment. Mouse strains with a constitutive or conditional eosinophil deficiency, or with an eosinophil-specific ablation of Tgfb, lack bacterially induced neuropilin-negative, RORγt-positive gastrointestinal Treg populations in models of Helicobacter pylori, Helicobacter hepaticus and Citrobacter rodentium infection, as well as in the steady state colon and upon oral ovalbumin challenge. Treg priming in lymph nodes appears not to be impaired. Eosinophil-dependent tissue-resident Tregs express CTLA4, ICOS, CD39 and T-bet in addition to RORγt. Eosinophils reside in close proximity to Tregs in infected tissues, and specifically induce the expansion of newly formed Tregs, but not conventional T-cells in vivo and in vitro. TGF-β expression in eosinophils is induced by bacterial contact and during allergen exposure. Specific Tgfb ablation in eosinophils and the associated Treg defects result in excessive T-cell responses in the examined Th2- but not Th1-polarized settings. [Image: see text

TGF-β production by eosinophils drives the expansion of peripherally induced neuropilin - RORγt + regulatory T-cells during bacterial and allergen challenge

Eosinophils are best known for their effector functions in settings of parasitic infection or allergen challenge, but have also increasingly been implicated in immune regulation at mucosal sites. Here, we show using bacterial infection and antigen challenge models that extrathymic Foxp3+ regulatory T-cells that arise de novo in the context of bacterial infection require an intact eosinophil compartment. Mouse strains with a constitutive or conditional eosinophil deficiency, or with an eosinophil-specific ablation of Tgfb, lack bacterially induced neuropilin-negative, RORγt-positive gastrointestinal Treg populations in models of Helicobacter pylori, Helicobacter hepaticus and Citrobacter rodentium infection, as well as in the steady state colon and upon oral ovalbumin challenge. Treg priming in lymph nodes appears not to be impaired. Eosinophil-dependent tissue-resident Tregs express CTLA4, ICOS, CD39 and T-bet in addition to RORγt. Eosinophils reside in close proximity to Tregs in infected tissues, and specifically induce the expansion of newly formed Tregs, but not conventional T-cells in vivo and in vitro. TGF-β expression in eosinophils is induced by bacterial contact and during allergen exposure. Specific Tgfb ablation in eosinophils and the associated Treg defects result in excessive T-cell responses in the examined Th2- but not Th1-polarized settings

Transmaternal Helicobacter pylori exposure reduces allergic airway inflammation in offspring through regulatory T cells.

Background: Transmaternal exposure to tobacco, microbes, nutrients, and other environmental factors shapes the fetal immune system through epigenetic processes. The gastric microbe Helicobacter pylori represents an ancestral constituent of the human microbiota that causes gastric disorders on the one hand and is inversely associated with allergies and chronic inflammatory conditions on the other. Objective: Here we investigate the consequences of transmaternal exposure to H pylori in utero and/or during lactation for susceptibility to viral and bacterial infection, predisposition to allergic airway inflammation, and development of immune cell populations in the lungs and lymphoid organs. Methods: We use experimental models of house dust mite- or ovalbumin-induced airway inflammation and influenza A virus or Citrobacter rodentium infection along with metagenomics analyses, multicolor flow cytometry, and bisulfite pyrosequencing, to study the effects of H pylori on allergy severity and immunologic and microbiome correlates thereof. Results: Perinatal exposure to H pylori extract or its immunomodulator vacuolating cytotoxin confers robust protective effects against allergic airway inflammation not only in first- but also second-generation offspring but does not increase susceptibility to viral or bacterial infection. Immune correlates of allergy protection include skewing of regulatory over effector T cells, expansion of regulatory T-cell subsets expressing CXCR3 or retinoic acid-related orphan receptor γt, and demethylation of the forkhead box P3 (FOXP3) locus. The composition and diversity of the gastrointestinal microbiota is measurably affected by perinatal H pylori exposure. Conclusion: We conclude that exposure to H pylori has consequences not only for the carrier but also for subsequent generations that can be exploited for interventional purposes. Keywords: Allergic airway inflammation; epigenetic regulation of allergy and asthma; immune regulation; immune tolerance; metagenomics; microbial interventions during pregnancy