Background & Aims Helicobacter pylori infection increases gastric Treg response, which may contribute to H pylori immune escape. We hypothesize that H pylori directs Treg skewing by way of dendritic cells and thus inhibits Th17 immunity. Methods Two-photon microscopy was used to locate dendritic cells in gastric lamina propria of mice. The induction of Th17 and Treg responses by bacteria-pulsed murine bone marrow–derived dendritic cells was analyzed by cytokine production and stimulation of T cell proliferation. The effect of VacA, CagA, TGF-β, and IL-10 on Th17/Treg balance was assessed. The in vivo significance of Tregs on the H pylori–specific Th17 response and H pylori density was determined using anti-CD25 neutralizing antibodies to deplete Tregs in mice. Results We showed that mucosal CD11c+ dendritic cells are located near the surface of normal gastric epithelium and their number increased after H pylori infection. Study of the direct interaction of dendritic cells with H pylori revealed a Treg-skewed response. The Treg skewing was independent of H pylori VacA and CagA and dependent on TGF-β and IL-10. In vivo Treg skewing by adoptive transfer of H pylori–pulsed DCs reduces the ratio of gastric IL-17/Foxp3 mRNA expressions. The depletion of CD25+ Tregs results in early reduction of H pylori density, which is correlated with enhanced peripheral H pylori–specific Th17, but not Th1, response. Conclusions Overall, our study indicates that H pylori alters the DC-polarized Th17/Treg balance towards a Treg-biased response, which suppresses the effective induction of H pylori–specific Th17 immunity.

Background & Aims Recently there has been emerging epidemiological data to suggest Helicobacter pylori (H. pylori) may protect against certain chronic inflammatory diseases such as inflammatory bowel disease (IBD). However, the mechanism for the observed inverse association between H. pylori and IBD has not been described. Methods The frequency of immunoregulatory (IRS) to immunostimulatory (ISS) sequences within the genome of various bacteria was calculated using MacVector software. The induction of type I IFN and IL-12 responses by DNA-pulsed murine bone marrow–derived dendritic cells (BMDC) and human plasmacytoid dendritic cells (pDC) was analyzed by cytokine production. The effect of H. pylori DNA on E. coli DNA production of type I IFN and IL-12 was assessed. The in vivo significance of H. pylori DNA suppression was assessed in a DSS-model of colitis. The systemic levels of type I IFN were assessed in H. pylori-colonized and non-colonized patients. Results We showed that H. pylori DNA has a significantly elevated IRS:ISS ratio. In vitro experiments revealed the inability of H. pylori DNA to stimulate type I IFN or IL-12 production from mouse BMDCs or human pDCs. Additionally, H. pylori DNA was able to suppress E. coli-DNA production of type I IFN and IL-12. Administration of H. pylori DNA prior to the induction of DSS colitis significantly ameliorated the severity of colitis as compared to E. coli DNA or vehicle control in both an acute and chronic model. Finally, the systemic levels of type I IFN were found to be lower in H. pylori-colonized patients versus non-colonized controls. Conclusions Overall, our study indicates that H pylori DNA has the ability to down-regulate pro-inflammatory responses from DCs and this may in part explain the inverse association between H. pylori and IBD.

The gut microbiota is essential for the maintenance of intestinal immune homeostasis and is responsible for breaking down dietary fiber into short-chain fatty acids (SCFAs). Butyrate, the most abundant bioactive SCFA in the gut, is a histone deacetylase inhibitor (HDACi), a class of drug that has potent immunomodulatory properties. This characteristic of butyrate, along with our previous discovery that conventional dendritic cells (DCs) are required for the development of experimental colitis, led us to speculate that butyrate may modulate DC function to regulate gut mucosal homeostasis. We found that butyrate, in addition to suppressing LPS-induced bone marrow-derived DC maturation and inhibiting DC IL-12 production, significantly induced IL-23 expression. The upregulation of mRNA subunit IL-23p19 at the pretranslational level was consistent with the role of HDACi on the epigenetic modification of gene expression. Furthermore, the mechanism of IL-23p19 upregulation was independent of Stat3 and ZBP89. Coculture of splenocytes with LPS-stimulated DCs pretreated with or without butyrate was performed and showed a significant induction of IL-17 and IL-10. We demonstrated further the effect of butyrate in vivo using dextran sulfate sodium (DSS)-induced colitis and found that the addition of butyrate in the drinking water of mice worsened DSS-colitis. This is in contrast to the daily intraperitoneal butyrate injection of DSS-treated mice, which mildly improved disease severity. Our study highlights a novel effect of butyrate in upregulating IL-23 production of activated DCs and demonstrates a difference in the host response to the oral vs. systemic route of butyrate administration.

We have shown that Helicobacter pylori induces tolerogenic programming of dendritic cells and inhibits the host immune response. Toll-like receptors (TLRs) represent a class of transmembrane pattern recognition receptors essential for microbial recognition and control of the innate immune response. In this study, we examined the role of TLRs in mediating H. pylori tolerogenic programming of dendritic cells and their impact on anti–H. pylori immunity using C57BL/6 wild-type and TLR2-knockout (TLR2KO) mice. We analyzed the response of TLR2KO bone marrow-derived dendritic cells (BMDCs) to H. pylori SS1 stimulation and the outcome of chronic H. pylori infection in TLR2KO mice. We showed that H. pylori–stimulated BMDCs upregulated the expression of TLR2, but not TLR4, TLR5, or TLR9. H. pylori-stimulated BMDCs from TLRKO mice induced lower Treg and Th17 responses, but a higher IFN-γ response compared to H. pylori-stimulated BMDCs from wild-type mice. In vivo analyses following an H. pylori infection of 2 months duration showed a lower degree of gastric H. pylori colonization in TLR2KO mice and more severe gastric immunopathology compared to WT mice. The gastric mucosa of the infected TLR2KO mice showed a lower mRNA expression of Foxp3, IL-10, and IL-17A, but higher expression of IFN-γ compared to the gastric mRNA expression in infected wild-type mice. Moreover, the H. pylori–specific Th1 response was higher and the Treg and Th17 responses were lower in the spleens of infected TLR2KO mice compared to infected WT mice. Our data indicate that H. pylori mediates immune tolerance through TLR2-derived signals and inhibits Th1 immunity, thus evading host defense. TLR2 may be an important target in the modulation of the host response to H. pylori.