Helicobacter pylori DNA decreases pro-inflammatory cytokine production by dendritic cells and attenuates dextran sodium sulphate-induced colitis.

BACKGROUND AND AIMS: Epidemiological data have recently emerged to suggest Helicobacter 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 (DC) was analysed by cytokine production. The effect of H pylori DNA on Escherichia 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 dextran sodium sulphate (DSS) model of colitis. The systemic levels of type I IFN were assessed in H pylori-colonised and non-colonised patients. RESULTS: 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 BMDC or human plasmacytoid DC. H pylori DNA was also able to suppress E coli DNA production of type I IFN and IL-12. The administration of H pylori DNA before the induction of DSS colitis significantly ameliorated the severity of colitis compared with 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-colonised patients than non-colonised controls. CONCLUSIONS: This study indicates that H pylori DNA has the ability to downregulate pro-inflammatory responses from DC and this may partly explain the inverse association between H pylori and IBD.

Helicobacter pylori-pulsed dendritic cells induce H. pylori-specific immunity in mice.

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. AIM: We studied the use of a dendritic cell (DC)-based vaccine against H. pylori infection in mice. METHODS: The cellular immune responses to murine bone marrow-derived DCs pulsed with phosphate-buffered saline (PBS-DC) or live H. pylori SS1 (HP-DC) were assessed in vitro and in vivo. The protective immunity against H. pylori SS1 oral challenge was compared between HP-DC or PBS-DC immunized mice. The effect of regulatory T-cell (Treg) depletion by anti-CD25 antibody on HP-DC vaccine efficacy was also evaluated. RESULTS: HP-DC induced a Th1-dominant response in vitro. In vivo, HP-DC immunized mice were characterized by a mixed Th1/Th2 peripheral immune response. However, in the stomach, HP-DC immunized mice expressed a higher level of IFN-gamma compared to PBS-DC immunized mice; no difference was found for interleukin-5 expressions in the stomach. A lower bacterial colonization post-H. pylori challenge was observed in HP-DC immunized mice compared to PBS-DC immunized mice with no significant difference in gastritis severity. H. pylori-specific Th1 response and protective immunity were further enhanced in vivo by depletion of Treg with anti-CD25 antibody. CONCLUSION: DC-based anti-H. pylori vaccine induced H. pylori-specific helper T-cell responses capable of limiting bacterial colonization. Our data support the critical role of effector cellular immune response in the development of H. pylori vaccine.

Aberrant T helper cell response in tumor-bearing mice limits the efficacy of dendritic cell vaccine.

Dendritic cell (DC) vaccine is a promising immunotherapy for malignancies, but its clinical efficacy has been questioned. Here we examined the mechanisms of treatment failure with DC vaccine in a murine colon cancer model. DC vaccination of naive mice prevents tumor implantation, but it is ineffective in tumor-bearing hosts despite the induction of tumor-specific CTL activity. Analyses of tumor-specific T helper cell type 1 (Th1)/T helper cell type 2 (Th2) responses showed that DC vaccine induced a mixed Th1/Th2 response in naive mice. Interestingly, CD4+ T cells from tumor-bearing mice showed a Th1-predominant response before DC vaccination but Th2 after DC vaccination. Furthermore, interleukin-10 production was higher in CD4+ T cells from vaccinated tumor-bearing mice than in CD4+ T cells from unvaccinated tumor-bearing mice. CD4+ T cells from mice treated with lipopolysaccharide (LPS)-matured DC fusion vaccine had lower production of interleukin-10 than CD4+ T cells from mice treated with non-LPS-treated DC vaccine. However, similar to the non-LPS-treated DC vaccine, the LPS-matured DC vaccine failed to suppress tumor growth and induced a Th2 predominant tumor-specific response in tumor-bearing mice. These results suggest that the presence of tumor in the host induces an aberrant CD4+ T cell response to DC vaccine, which may contribute to the failure of the vaccine to eradicate established tumors.

Somatostatin inhibits dendritic cell responsiveness to Helicobacter pylori.

Somatostatin is a regulatory peptide found in abundance in the stomach. We have previously shown that somatostatin is required for IL-4-mediated resolution of Helicobacter pylori gastritis. In the current study, we hypothesize that somatostatin acts directly on antigen-presenting cells in the stomach to lessen the severity of gastritis. To test this hypothesis, we first show that CD11c+ dendritic cells are present in the infected tissue of mice with H. pylori-induced gastritis. Pretreatment of bone marrow-derived dendritic cells with somatostatin results in decreased IL-12 production, and lower splenocyte proliferation induced by H. pylori-stimulated dendritic cells. Furthermore, octreotide, a somatostatin analogue, is more potent than somatostatin in suppressing IL-12 release by H. pylori-stimulated dendritic cells through an NF-kappaB-independent pathway. In addition, IL-4 stimulates somatostatin secretion from dendritic cells. In conclusion, somatostatin inhibits dendritic cell activation by H. pylori; a possible mechanism by which IL-4 mediates resolution of gastritis. We suggest that octreotide may be effective in treating immune-mediated diseases of the stomach.

Helicobacter pylori-secreted factors inhibit dendritic cell IL-12 secretion: a mechanism of ineffective host defense.

Helicobacter pylori evades host immune defenses and causes chronic gastritis. Immunity against intestinal pathogens is largely mediated by dendritic cells, yet the role of dendritic cells in acute H. pylori infection is largely unknown. We observed the recruitment of dendritic cells to the gastric mucosa of H. pylori-infected mice. Bone marrow-derived dendritic cells from mice responded to live H. pylori by upregulating the expression of proinflammatory cytokine mRNA (i.e., IL-1alpha, IL-1beta, and IL-6). The supernatant from dendritic cells stimulated with H. pylori for 18 h contained twofold higher levels of IL-12p70 than IL-10 and induced the proliferation of syngeneic splenocytes and type 1 T helper cell cytokine release (IFN-gamma and TNF-alpha). These responses were significantly lower compared with those induced by Acinetobacter lwoffi, another gastritis-causing pathogen more susceptible to host defenses. Analysis of whole H. pylori sonicate revealed the presence of a heat-stable factor secreted from H. pylori that specifically inhibited IL-12 but not IL-10 release from dendritic cells activated by A. lwoffi. Our findings suggest that dendritic cells participate in the host immune response against H. pylori and that their suppression by H. pylori may explain why infected hosts fail to prevent bacterial colonization.