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.

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.

Dendritic cells (DCs) are essential mediators of the host immune response to surrounding microbes. In this study, we investigate the role of DCs in the pathogenesis of a widely used colitis model, dextran sulfate sodium-induced colitis. The effect of dextran sulfate sodium on the production of proinflammatory cytokines and chemokines by bone marrow-derived DCs (BM-DCs) was analyzed. BM-DCs were adoptively transferred into C57BL/6 mice or DCs were ablated using transgenic CD11c-DTR/GFP mice before treatment with 5% dextran sulfate sodium in drinking water. We found that dextran sulfate sodium induced production of proinflammatory cytokines (IL-12 and TNF-α) and chemokines (KC, MIP-1α, MIP-2, and MCP-1) by DCs. Adoptive transfer of BM-DCs exacerbated dextran sulfate sodium colitis while ablation of DCs attenuated the colitis. We conclude that DCs are critical in the development of acute dextran sulfate sodium colitis and may serve a key role in immune balance of the gut mucosa.

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Background-The growing concern over the emergence of antibiotic-resistant Helicobacter pylori infection is propelling the development of an efficacious vaccine to control this highly adaptive organism.