Helicobacter pylori Infection of the Gastric Mucosa

The role of toll-like receptors in peptic ulcer disease

Helicobacter pylori (HP) is the primary etiologic factor that induces events in the immune system that lead to peptic ulcers. Toll-like receptors (TLRs) are an important part of the innate immune system, as they play pivotal roles in pathogen-associated molecular pattern (PAMP) recognition of HP as well host-associated damage-associated molecular patterns (DAMPs). Recent advancements such as COX-2 production, LPS recognition through TLR2, CagL, and CagY protein of HP activating TLR5, TLR9 activation via type IV secretion system (T4SS) using DNA transfer, TLR polymorphisms, their adaptor molecules, cytokines, and other factors play a significant role in PUD. Thus, some novel PUD treatments including Chuyou Yuyang granules, function by TLR4/NF-κB signaling pathway suppression and TNF-α and IL-18 inhibition also rely on TLR signaling. Similarly glycyrrhetinic acid (GA) treatment activates TLR-4 in Ana-1 cells not via TRIF, but via MYD88 expression, which is significantly upregulated to cure PUD. Therefore, understanding TLR signaling complexity and its resultant immune modulation after host-pathogen interactions is pivotal to drug and vaccine development for other diseases as well including cancer and recent pandemic COVID-19. In this review, we summarize the TLRs and HP interaction; its pathophysiology-related signaling pathways, polymorphisms, and pharmaceutical approaches toward PUD.

The frequency of circulating integrin α4β7+ cells correlates with protection against Helicobacter pylori infection in immunized mice

BACKGROUND

Chronic Helicobacter pylori infection is the cause of peptic ulcers in a subpopulation of individuals and a risk factor for the development of gastric cancer. A vaccine against H pylori infection can prevent the acquisition of the infection and protect against reinfections. Clinical trials to date evaluating the efficacy of H pylori vaccines in human challenge models have shown moderate to poor protection with difficulties in predicting efficacy. Thus, while further studies are needed to design an effective vaccine, we also need to find relevant correlates for vaccine efficacy.

OBJECTIVE

To find immune correlates to vaccine efficacy, the frequencies of neutrophils, eosinophils and inflammatory monocytes and CD4⁺ T-cell memory and mucosa homing integrin α4β7⁺ cells were assessed by flow cytometry in the blood of mice after vaccination.

MATERIALS AND METHODS

H pylori antigens and cholera toxin or the multiple mutant CT (mmCT) were administered via the sublingual (SL) and intragastric route (IG). The vaccinated mice were infected with H pylori strain SS1 bacteria, and colonization in the stomach and immune responses were evaluated.

RESULTS

The H pylori vaccine was effective in reducing bacterial load in the stomach of mice and enhancing immune responses compared to unvaccinated infection controls. In the blood of mice after SL or IG route of vaccination, we observed changes in frequencies of innate and adaptive immune cell subsets compared to infection controls. Remarkably, the frequency of circulating mucosal homing α4β7⁺ CD4⁺ T cells after vaccination correlated with low bacterial load in the stomach of individual mice irrespective of the immunization route.

CONCLUSIONS

Our study shows that the innate and adaptive immune cell subsets can be measured in the blood after vaccination and that increased frequency of α4β7⁺ CD4⁺ in the blood after immunization could be used as a predictive marker for the efficacy of vaccine against H pylori infection.

An oral alpha-galactosylceramide adjuvanted Helicobacter pylori vaccine induces protective IL-1R- and IL-17R-dependent Th1 responses

Helicobacter pylori causes chronic gastric infection that can lead to peptic ulcers and is an identified risk factor for gastric cancer development. Although much effort has been put into the development of a Helicobacter pylori vaccine over the last three decades, none has yet reached clinical application. Specific challenges pertaining to effective H. pylori vaccine development include the lack of proven vaccine-effective antigens and safe mucosal adjuvants to enhance local immune responses as well as the lack of accepted correlates of protection. Herein, we demonstrate that prophylactic intragastric immunisation with a whole-cell killed H. pylori antigen administered together with the non-toxic oral adjuvant α-galactosylceramide (α-GalCer) induced effective immune protection against H. pylori infection in mice, which was of similar magnitude as when using the “gold standard” cholera toxin as adjuvant. We further describe that this α-GalCer-adjuvanted vaccine formulation elicited strong intestinal and systemic Th1 responses as well as significant antigen-specific mucosal and systemic antibody responses. Finally, we report that the protective intestinal Th1 responses induced by α-GalCer are dependent on CD1d, IL-1R as well as IL-17R signalling. In summary, our results show that α-GalCer is a promising adjuvant for inclusion in an oral vaccine against H. pylori infection.

Infection by Helicobacter pylori is highly prevalent in humans and can lead to chronic inflammation and gastric cancer, but to date no effective vaccine has been approved for clinical use owing to the lack of appropriate antigens and of safe mucosal adjuvants that can produce protective and durable immunity to the bacterium. Sukanya Raghavan, Ed Lavelle and colleagues now show that prophylactic intragastric administration of an inactivated whole-cell H. pylori preparation, together with the oral adjuvant α-galactosylceramide, reduced H. pylori infection in mice by eliciting a protective mucosal and systemic T_H1 response. The immunisation triggered antigen-specific antibodies and interferon-γ that prevented effective colonisation of H. pylori after challenge in a process dependent on the CD1d, IL-1 receptor and IL-17 receptor pathways. The reported enhanced immune response to this orally adjuvanted vaccine formulation paves the way for further studies of its safety and efficacy.

Induction of mucosal immune responses against Helicobacter pylori infection after sublingual and intragastric route of immunization

There is a current lack of effective mucosal vaccines against major gastroenteric pathogens and particularly against Helicobacter pylori, which causes a chronic infection that can lead to peptic ulcers and gastric cancer in a subpopulation of infected individuals. Mucosal CD4⁺ T-cell responses have been shown to be essential for vaccine-induced protection against H. pylori infection. The current study addresses the influence of the adjuvant and site of mucosal immunization on early CD4⁺ T-cell priming to H. pylori antigens. The vaccine formulation consisted of H. pylori lysate antigens and mucosal adjuvants, cholera toxin (CT) or a detoxified double-mutant heat-labile enterotoxin from Escherichia coli (dmLT), which were administered by either the sublingual or intragastric route. We report that in vitro, adjuvants CT and dmLT induce up-regulation of pro-inflammatory gene expression in purified dendritic cells and enhance the H. pylori-specific CD4⁺ T-cell response including interleukin-17A (IL-17A), interferon-γ (IFN-γ) and tumour necrosis factor-α (TNF-α) secretion. In vivo, sublingual immunization led to an increased frequency of IL-17A⁺ , IFN-γ⁺ and TNF-α⁺ secreting CD4⁺ T cells in the cervical lymph nodes compared with in the mesenteric lymph nodes after intragastric immunization. Subsequently, IL-17A⁺ cells were visualized in the stomach of sublingually immunized and challenged mice. In summary, our results suggest that addition of an adjuvant to the vaccine clearly activated dendritic cells, which in turn, enhanced CD4⁺ T-cell cytokines IL-17A, IFN-γ and TNF-α responses, particularly in the cervical lymph nodes after sublingual vaccination.