Mast cells are critical mediators of vaccine-induced Helicobacter clearance in the mouse model

An intranasal influenza virus vector vaccine protects against Helicobacter pylori in mice

Helicobacter pylori is a human pathogen that infects almost half of the population. Antibiotic resistance in H. pylori threatens health and increases the demand for prophylactic and therapeutic vaccines. Traditional oral vaccine research faces considerable challenges because of the epithelial barrier, potential enterotoxicity of adjuvants, and the challenging conditions of the gastric environment. We developed an intranasal influenza A virus (IAV) vector vaccine based on two live attenuated influenza viruses with modified acidic polymerase protein (PA) genes encoding the A subunit of H. pylori neutrophil-activating protein (NapA), named IAV-NapA, including influenza virus A/WSN/33 (WSN)-NapA and A/Puerto Rico/8/34 (PR8)-NapA. These recombinant influenza viruses were highly attenuated and exhibited strong immunogenicity in mice. Vaccination with IAV-NapA induced antigen-specific humoral and mucosal immune responses while stimulating robust Th1 and Th17 cell immune responses in mice. Our findings suggest that prophylactic and therapeutic vaccination with influenza virus vector vaccines significantly reduces colonization of H. pylori and inflammation in the stomach of mice.IMPORTANCEHelicobacter pylori is the most common cause of chronic gastritis and leads to severe gastroduodenal pathology in some patients. Many studies have shown that Th1 and Th17 cellular and gastric mucosal immune responses are critical in reducing H. pylori load. IAV vector vaccines can stimulate these immune responses while overcoming potential adjuvant toxicity and antigen dosing issues. To date, no studies have demonstrated the role of live attenuated IAV vector vaccines in preventing and treating H. pylori infection. Our work indicates that vaccination with IAV-NapA induces antigen-specific humoral, cellular, and mucosal immunity, producing a protective and therapeutic effect against H. pylori infection in BALB/c mice. This undescribed H. pylori vaccination approach may provide valuable information for developing vaccines against H. pylori infection.

GM-CSF is key in the efficacy of vaccine-induced reduction of Helicobacter pylori infection

BACKGROUND

Helicobacter pylori (H. pylori) colonizes the human gastric mucosa with a high worldwide prevalence. Currently, H. pylori is eradicated by the use of antibiotics. However, elevated antibiotic resistance suggests new therapeutic strategies need to be envisioned: one approach being prophylactic vaccination. Pre-clinical and clinical data show that a urease-based vaccine is efficient in decreasing H. pylori infection through the mobilization of T helper (Th) cells, especially Th17 cells. Th17 cells produce interleukins such as IL-22 and IL-17, among others, and are key players in vaccine efficacy. Recently, granulocyte-macrophage colony-stimulating factor (GM-CSF)-producing Th17 cells have been identified.

AIM

This study explores the possibility that GM-CSF plays a role in the reduction of H. pylori infection following vaccination.

RESULTS

We demonstrate that GM-CSF⁺ IL-17⁺ Th17 cells accumulate in the stomach mucosa of H. pylori infected mice during the vaccine-induced reduction of H. pylori infection. Secondly, we provide evidence that vaccinated GM-CSF deficient mice only modestly reduce H. pylori infection. Conversely, we observe that an increase in GM-CSF availability reduces H. pylori burden in chronically infected mice. Thirdly, we show that GM-CSF, by acting on gastric epithelial cells, promotes the production of βdefensin3, which exhibits H. pylori bactericidal activities.

CONCLUSION

Taken together, we demonstrate a key role of GM-CSF, most probably originating from Th17 cells, in the vaccine-induced reduction of H. pylori infection.

Selected recent advances in understanding the role of human mast cells in health and disease

Mast cells are highly granular tissue-resident cells and key drivers of inflammation, particularly in allergies as well as in other inflammatory diseases. Most mast cell research was initially conducted in rodents but has increasingly shifted to the human system, with the advancement of research technologies and methodologies. Today we can analyze primary human cells including rare subpopulations, we can produce and maintain mast cells isolated from human tissues, and there are several human mast cell lines. These tools have substantially facilitated our understanding of their role and function in different organs in both health and disease. We can now define more clearly where human mast cells originate from, how they develop, which mediators they store, produce de novo, and release, how they are activated and by which receptors, and which neighbouring cells they interact with and by which mechanisms. Considerable progress has also been made regarding the potential contribution of mast cells to disease, which, in turn, has led to the development of novel approaches for preventing key pathogenic effects of mast cells, heralding the era of mast cell-targeted therapeutics. In this review, we present and discuss a selection of some of the most significant advancements and remaining gaps in our understanding of human mast cells during the last 25 years, with a focus on clinical relevance.

Helicobacter pylori infection has a detrimental impact on the efficacy of cancer immunotherapies

OBJECTIVE

In this study, we determined whether Helicobacter pylori (H. pylori) infection dampens the efficacy of cancer immunotherapies.

DESIGN

Using mouse models, we evaluated whether immune checkpoint inhibitors or vaccine-based immunotherapies are effective in reducing tumour volumes of H. pylori-infected mice. In humans, we evaluated the correlation between H. pylori seropositivity and the efficacy of the programmed cell death protein 1 (PD-1) blockade therapy in patients with non-small-cell lung cancer (NSCLC).

RESULTS

In mice engrafted with MC38 colon adenocarcinoma or B16-OVA melanoma cells, the tumour volumes of non-infected mice undergoing anticytotoxic T-lymphocyte-associated protein 4 and/or programmed death ligand 1 or anti-cancer vaccine treatments were significantly smaller than those of infected mice. We observed a decreased number and activation status of tumour-specific CD8⁺ T cells in the tumours of infected mice treated with cancer immunotherapies independent of the gut microbiome composition. Additionally, by performing an in vitro co-culture assay, we observed that dendritic cells of infected mice promote lower tumour-specific CD8⁺ T cell proliferation. We performed retrospective human clinical studies in two independent cohorts. In the Dijon cohort, H. pylori seropositivity was found to be associated with a decreased NSCLC patient survival on anti-PD-1 therapy. The survival median for H. pylori seropositive patients was 6.7 months compared with 15.4 months for seronegative patients (p=0.001). Additionally, in the Montreal cohort, H. pylori seropositivity was found to be associated with an apparent decrease of NSCLC patient progression-free survival on anti-PD-1 therapy.

CONCLUSION

Our study unveils for the first time that the stomach microbiota affects the response to cancer immunotherapies and that H. pylori serology would be a powerful tool to personalize cancer immunotherapy treatment.

Isolation of lymphocytes from the human gastric mucosa

Flow cytometry is widely used for lymphocyte immunophenotyping in clinical settings. However, few studies have applied it for analyzing lymphocytes of the gastric mucosa. This review offers an overview of methodologies for isolating lymphocytes from the human stomach. Previously reported articles were reviewed, focusing on procedures for isolating human gastric mucosal lymphocytes. Helicobacter pylori-associated peptic diseases and gastric cancer are two major subjects of research in this field. Enzymatic dissociation, mechanical dissociation, or a combination of the two have been used to isolate lymphocytes from the stomach. Intra-epithelial and lamina propria lymphocytes were separately isolated in several studies. We also summarize the history and present trends in analyzing lymphocytes in patients with gastric disease.

Gastric eosinophils are detrimental for Helicobacter pylori vaccine efficacy

Helicobacter pylori (Hp) colonizes the human gastric mucosa with a high worldwide prevalence. Currently, Hp can be eradicated by the use of antibiotics. Due to the increase of antibiotic resistance, new therapeutic strategies need to be devised: one such approach being prophylactic vaccination. Pre-clinical and clinical data showed that a urease-based vaccine is efficient in decreasing Hp infection through the mobilization of T helper (Th)-dependent immune effectors, including eosinophils. Preliminary data have shown that upon vaccination and subsequent Hp infection, eosinophils accumulate in the gastric mucosa, suggesting a possible implication of this granulocyte subset in the vaccine-induced reduction of Hp infection. In our study, we confirm that activated eosinophils, expressing CD63, CD40, MHCII and PD-L1 at their cell surface, infiltrate the gastric mucosa during vaccine-induced reduction of Hp infection. Strikingly, we provide evidence that bone marrow derived eosinophils efficiently kill Hp in vitro, suggesting that eosinophils may participate to the vaccine-induced reduction of Hp infection. However, conversely to our expectations, the absence of eosinophils does not decrease the efficacy of this Hp vaccine in vivo. Indeed, vaccinated mice that have been genetically ablated of the eosinophil lineage or that have received anti-Sialic acid-binding immunoglobulin-like lectin F eosinophil-depleting antibodies, display a lower Hp colonization when compared to their eosinophil sufficient counterparts. Although the vaccine induces similar urease-specific humoral and Th responses in both eosinophil sufficient and deficient mice, a decreased production of anti-inflammatory cytokines, such as IL-10, TGFβ, and calgranulin B, was specifically observed in eosinophil depleted mice. Taken together, our results suggest that gastric eosinophils maintain an anti-inflammatory environment, thus sustaining chronic Hp infection. Because eosinophils are one of the main immune effectors mobilized by Th2 responses, our study strongly suggests that the formulation of an Hp vaccine needs to include an adjuvant that preferentially primes Hp-specific Th1/Th17 responses.

Mast Cells in the Skin: Defenders of Integrity or Offenders in Inflammation?

Mast cells (MCs) are best-known as key effector cells of immediate-type allergic reactions that may even culminate in life-threatening anaphylactic shock syndromes. However, strategically positioned at the host–environment interfaces and equipped with a plethora of receptors, MCs also play an important role in the first-line defense against pathogens. Their main characteristic, the huge amount of preformed proinflammatory mediators embedded in secretory granules, allows for a rapid response and initiation of further immune effector cell recruitment. The same mechanism, however, may account for detrimental overshooting responses. MCs are not only detrimental in MC-driven diseases but also responsible for disease exacerbation in other inflammatory disorders. Focusing on the skin as the largest immune organ, we herein review both beneficial and detrimental functions of skin MCs, from skin barrier integrity via host defense mechanisms to MC-driven inflammatory skin disorders. Moreover, we emphasize the importance of IgE-independent pathways of MC activation and their role in sustained chronic skin inflammation and disease exacerbation.

Role of Helicobacter pylori Eradication in Chronic Spontaneous Urticaria: A Propensity Score Matching Analysis

Objective

To investigate the role of Helicobacter pylori (HP) eradication in chronic spontaneous urticaria (CSU) treatment.

Methods

Retrospective analysis was performed on the clinical data of 522 patients with CSU who underwent a HP breath test in Hangzhou Third People’s Hospital between January 2018 and December 2019. The CSU-HP(+) group consisted of patients with CSU and HP infection, who were treated with antihistamines combined with HP eradication therapy. The CSU-HP(-) group consisted of patients with CSU alone, who were treated with antihistamines. Propensity score matching (PSM) analysis, using the nearest neighbor matching method on a 1:1 basis, was performed to ensure the characteristics of the CSU-HP(+) and CSU-HP(-) groups were similar. Factors, including age, gender, white blood cells, red blood cells, platelets, alanine transaminase, creatinine, immunoglobulin E, and pre-treatment urticaria activity score (UAS), were matched to obtain a balanced cohort of patients in each group. Therapeutic effects were compared after matching. t-tests, Χ² test, and McNemar’s test were used for comparison between the two groups before and after matching.

Results

Patients in the CSU-HP(+) group reported significantly more gastrointestinal symptoms than those in the CSU-HP(-) group. UAS scores in the second week of treatment were significantly different between the two groups. After 3 months, the recurrence rate in the CSU-HP(+) group was lower than in the CSU-HP(-) group.

Conclusion

Eradication of HP infection in patients with CSU helps relieve gastrointestinal symptoms, improves the therapeutic effect of CSU within 2 weeks, and reduces the recurrence rate 3 months after treatment.

Immunity and Vaccine Development Against Helicobacter pylori

Helicobacter pylori is a highly-adapted gastrointestinal pathogen of humans and the immunology of this chronic infection is extremely complex. Despite the availability of antibiotic therapy, the global incidence of H. pylori infection remains high, particularly in low to middle-income nations. Failure of therapy and the spread of antibiotic resistance among the bacteria are significant problems and provide impetus for the development of new therapies and vaccines to treat or prevent gastric ulcer, and gastric carcinoma. The expansion of knowledge on gastric conventional and regulatory T cell responses, and the role of T_H17 in chronic gastritis from studies in mouse models and patients have provided valuable insights into how gastritis is initiated and maintained. The development of human challenge models for testing candidate vaccines has meant a unique opportunity to study acute infection, but the field of vaccine development has not progressed as rapidly as anticipated. One clear lesson learned from previous studies is that we need a better understanding of the immune suppressive mechanisms in vivo to be able to design vaccine strategies. There is still an urgent need to identify practical surrogate markers of protection that could be deployed in future field vaccine trials. Important developments in our understanding of the chronic inflammatory response, progress and problems arising from human studies, and an outlook for the future of clinical vaccine trials will be discussed.

Gastric Subserous Vaccination With Helicobacter pylori Vaccine: An Attempt to Establish Tissue-Resident CD4+ Memory T Cells and Induce Prolonged Protection

Tissue-resident memory T (Trm) cells are enriched at the sites of previous infection and required for enhanced protective immunity. However, the emergence of Trm cells and their roles in providing protection are unclear in the field of Helicobacter pylori (H. pylori) vaccinology. Here, our results suggest that conventional vaccine strategies are unable to establish a measurable antigen (Ag)-specific memory cell pool in stomach; in comparison, gastric subserous injection of mice with micro-dose of Alum-based H. pylori vaccine can induce a pool of local CD4+ Trm cells. Regional recruitment of Ag-specific CD4+ T cells depends on the engagement of Ag and adjuvant-induced inflammation. Prior subcutaneous vaccination enhanced this recruitment. A stable pool of Ag-specific CD4+ T cells can be detected for 240 days. Two weeks of FTY720 administration in immune mice suggests that these cells do not experience the recirculation. Immunohistochemistry results show that close to the vaccination site, abundant CD4+T cells locate on epithelial niches, independent of lymphocyte cluster. Paradigmatically, Ag-specific CD4+ T cells with a phenotype of CD69+CD103- are preferential on lymphocytes isolated from epithelium. Upon Helicobacter infection, CD4+ Trm cells orchestrate a swift recall response with the recruitment of circulating antigen-specific Th1/Th17 cells to trigger a tissue-wide pathogen clearance. This study investigates the vaccine-induced gastric CD4+ Trm cells in a mice model, and highlights the need for designing a vaccine strategy against H. pylori by establishing the protective CD4+ Trm cells.

Maf deficiency in T cells dysregulates Treg - TH17 balance leading to spontaneous colitis

The maintenance of homeostasis in the gut is a major challenge for the immune system. Here we demonstrate that the transcription factor MAF plays a central role in T cells for the prevention of gastro-intestinal inflammation. Conditional knock out mice lacking Maf in all T cells developed spontaneous late-onset colitis, correlating with a decrease of FOXP3⁺RORγt⁺ T cells proportion, dampened IL-10 production in the colon and an increase of inflammatory T_H17 cells. Strikingly, FOXP3⁺ specific conditional knock out mice for MAF did not develop colitis and demonstrated normal levels of IL-10 in their colon, despite the incapacity of regulatory T cells lacking MAF to suppress colon inflammation in Rag1^−/− mice transferred with naïve CD4⁺ T cells. We showed that one of the cellular sources of IL-10 in the colon of these mice are T_H17 cells. Thus, MAF is critically involved in the maintenance of the gut homeostasis by regulating the balance between T_reg and T_H17 cells either at the level of their differentiation or through the modulation of their functions.

The contribution of mast cells to bacterial and fungal infection immunity

Mast cells are hematopoietic progenitor-derived, granule-containing immune cells that are widely distributed in tissues that interact with the external environment, such as the skin and mucosal tissues. It is well-known that mast cells are significantly involved in IgE-mediated allergic reactions, but because of their location, it has also been long hypothesized that mast cells can act as sentinel cells that sense pathogens and initiate protective immune responses. Using mast cell or mast cell protease-deficient murine models, recent studies by our groups and others indicate that mast cells have pleiotropic regulatory roles in immunological responses against pathogens. In this review, we discuss studies that demonstrate that mast cells can either promote host resistance to infections caused by bacteria and fungi or contribute to dysregulated immune responses that can increase host morbidity and mortality. Overall, these studies indicate that mast cells can influence innate immune responses against bacterial and fungal infections via multiple mechanisms. Importantly, the contribution of mast cells to infection outcomes depends in part on the infection model, including the genetic approach used to assess the influence of mast cells on host immunity, hence highlighting the complexity of mast cell biology in the context of innate immune responses.

More than just antibodies: Protective mechanisms of a mucosal vaccine against fish pathogen Flavobacterium columnare

A recently developed attenuated vaccine for Flavobacterium columnare has been demonstrated to provide superior protection for channel catfish, Ictalurus punctatus, against genetically diverse columnaris isolates. We were interested in examining the mechanisms of this protection by comparing transcriptional responses to F. columnare challenge in vaccinated and unvaccinated juvenile catfish. Accordingly, 58 day old fingerling catfish (28 days post-vaccination or unvaccinated control) were challenged with a highly virulent F. columnare isolate (BGSF-27) and gill tissues collected pre-challenge (0 h), and 1 h and 2 h post infection, time points previously demonstrated to be critical in early host-pathogen interactions. Following RNA-sequencing and transcriptome assembly, differential expression (DE) analysis within and between treatments revealed several patterns and pathways potentially underlying improved survival of vaccinated fish. Most striking was a pattern of dramatically higher basal expression of an array of neuropeptides (e.g. somatostatin), hormones, complement factors, and proteases at 0 h in vaccinated fish. Previous studies indicate these are likely the preformed mediators of neuroendocrine cells and/or eosinophilic granular (mast-like) cells within the fish gill. Following challenge, these elements fell to almost undetectable levels (>100-fold downregulated) by 1 h in vaccinated fish, suggesting their rapid release and/or cessation of synthesis following degranulation. Concomitantly, levels of pro-inflammatory cytokines (IL-1b, IL-8, IL-17) were induced in unvaccinated fish. In contrast, in vaccinated catfish, we observed widespread induction of genes needed for collagen deposition and tissue remodeling. Taken together, our results indicate an important component of vaccine protection in fish mucosal tissues may be the sensitization, proliferation and arming of resident secretory cells in the period between primary and secondary challenge.

IL-22-induced antimicrobial peptides are key determinants of mucosal vaccine-induced protection against H. pylori in mice

Despite the recent description of the mucosal vaccine-induced reduction of Helicobacter pylori natural infection in a phase 3 clinical trial, the absence of immune correlates of protection slows the final development of the vaccine. In this study, we evaluated the role of interleukin (IL)-22 in mucosal vaccine-induced protection. Gastric IL-22 levels were increased in mice intranasally immunized with urease+cholera toxin and challenged with H. felis, as compared with controls. Flow cytometry analysis showed that a peak of CD4+IL-22+IL-17+ T cells infiltrating the gastric mucosa occurred in immunized mice in contrast to control mice. The inhibition of the IL-22 biological activity prevented the vaccine-induced reduction of H. pylori infection. Remarkably, anti-microbial peptides (AMPs) extracted from the stomachs of vaccinated mice, but not from the stomachs of non-immunized or immunized mice, injected with anti-IL-22 antibodies efficiently killed H. pylori in vitro. Finally, H. pylori infection in vaccinated RegIIIβ-deficient mice was not reduced as efficiently as in wild-type mice. These results demonstrate that IL-22 has a critical role in vaccine-induced protection, by promoting the expression of AMPs, such as RegIIIβ, capable of killing Helicobacter. Therefore, it can be concluded that urease-specific memory Th17/Th22 cells could constitute immune correlates of vaccine protection in humans.

A 21-35 kDa Mixed Protein Component from Helicobacter pylori Activates Mast Cells Effectively in Chronic Spontaneous Urticaria

BACKGROUND

Helicobacter pylori (H. pylori) seem to involve in the etiology of chronic spontaneous urticaria (CSU). But studies of the pathogenic mechanism are very little.

METHODS

In this study, we detected the serum-specific anti-H. pylori IgG and IgE antibodies in 211 CSU and 137 normal subjects by enzyme-linked immunosorbent assay (ELISA), evaluated the direct activation effects of H. pylori preparations and its protein components on human LAD₂ mast cell line in vitro, and analyzed the specific protein ingredients and functions of the most effective H. pylori mixed protein component using liquid chromatography-mass spectrometry and ELISA assay.

RESULTS

In CSU patients, the positive rate of anti-H. pylori IgG positive rate was significantly higher than that in normal controls, and the anti-H. pylori IgE levels had no statistical difference between H. pylori-infected patients with and without CSU. Further studies suggested that H. pylori preparations can directly activate human LAD₂ mast cell line in a dose-dependent manner and its most powerful protein component was a mixture of 21-35 kDa proteins. Moreover, the 21-35 kDa mixed protein component mainly contained 23 kinds of proteins, which can stimulate the release of histamine, TNF-a, IL-3, IFN-γ, and LTB4 by LAD₂ cells in a dose-dependent or time-dependent manner.

CONCLUSIONS

A 21-35 kDa mixed protein component should be regarded as the most promising pathogenic factor contributing to the CSU associated with H. pylori infection.

Use of VacA as a Vaccine Antigen

One of the major toxins secreted by H. pylori is the Vacuolating cytotoxin A (VacA) named after its ability to induce the formation of “vacuole”-like membrane vesicles in the cytoplasm of gastric cells. VacA has been associated with the disruption of mitochondrial functions, stimulation of apoptosis, blockade of T cell proliferation and promotion of regulatory T cells, thereby making it a promising vaccine target. Immunity to bacterial virulence factors is well known to protect humans against bacterial infections; hence, detoxified VacA has been evaluated as a vaccine antigen. Our short review summarizes the pre-clinical and clinical data that have been published on the use of VacA in the development of the H. pylori vaccine.

Role of Inflammatory Monocytes in Vaccine-Induced Reduction of Helicobacter felis Infection

Despite the proven ability of immunization to reduce Helicobacter infection in mouse models, the precise mechanism of protection has remained elusive. In this study, we evaluated the role of inflammatory monocytes in the vaccine-induced reduction of Helicobacter felis infection. We first showed by using flow cytometric analysis that Ly6C(low) major histocompatibility complex class II-positive chemokine receptor type 2 (CCR2)-positive CD64(+) inflammatory monocytes accumulate in the stomach mucosa during the vaccine-induced reduction of H. felis infection. To determine whether inflammatory monocytes played a role in the protection, these cells were depleted with anti-CCR2 depleting antibodies. Indeed, depletion of inflammatory monocytes was associated with an impaired vaccine-induced reduction of H. felis infection on day 5 postinfection. To determine whether inflammatory monocytes had a direct or indirect role, we studied their antimicrobial activities. We observed that inflammatory monocytes produced tumor necrosis factor alpha and inducible nitric oxide synthase (iNOS), two major antimicrobial factors. Lastly, by using a Helicobacter in vitro killing assay, we showed that mouse inflammatory monocytes and activated human monocytes killed H. pylori in an iNOS-dependent manner. Collectively, these data show that inflammatory monocytes play a direct role in the immunization-induced reduction of H. felis infection from the gastric mucosa.

Differential inflammatory response to Helicobacter pylori infection: etiology and clinical outcomes

The bacterial pathogen Helicobacter pylori commonly colonizes the human gastric mucosa during early childhood and persists throughout life. The organism has evolved multiple mechanisms for evading clearance by the immune system and, despite inducing inflammation in the stomach, the majority of infections are asymptomatic. H. pylori is the leading cause of peptic ulcer disease and gastric cancer. However, disease outcomes are related to the pattern and severity of chronic inflammation in the gastric mucosa, which in turn is influenced by both bacterial and host factors. Despite over 2 decades of intensive research, there remains an incomplete understanding of the circumstances leading to disease development, due to the fascinating complexity of the host-pathogen interactions. There is accumulating data concerning the virulence factors associated with increased risk of disease, and the majority of these have pro-inflammatory activities. Despite this, only a small proportion of those infected with virulent strains develop disease. Several H. pylori virulence factors have multiple effects on different cell types, including the induction of pro- and anti-inflammatory, immune stimulatory, and immune modulatory responses. The expression of multiple virulence factors is also often linked, making it difficult to assess the meaning of their effects in isolation. Overall, H. pylori is thought to usually modulate inflammation and limit acute damage to the mucosa, enabling the bacteria to persist. If this delicate balance is disturbed, disease may then develop.

Immune responses to Helicobacter pylori infection

Helicobacter pylori (H. pylori) infection is one of the most common infections in human beings worldwide. H. pylori express lipopolysaccharides and flagellin that do not activate efficiently Toll-like receptors and express dedicated effectors, such as γ-glutamyl transpeptidase, vacuolating cytotoxin (vacA), arginase, that actively induce tolerogenic signals. In this perspective, H. pylori can be considered as a commensal bacteria belonging to the stomach microbiota. However, when present in the stomach, H. pylori reduce the overall diversity of the gastric microbiota and promote gastric inflammation by inducing Nod1-dependent pro-inflammatory program and by activating neutrophils through the production of a neutrophil activating protein. The maintenance of a chronic inflammation in the gastric mucosa and the direct action of virulence factors (vacA and cytotoxin-associated gene A) confer pro-carcinogenic activities to H. pylori. Hence, H. pylori cannot be considered as symbiotic bacteria but rather as part of the pathobiont. The development of a H. pylori vaccine will bring health benefits for individuals infected with antibiotic resistant H. pylori strains and population of underdeveloped countries.

Mast cell mediator responses and their suppression by pathogenic and commensal microorganisms

Mast cells (MCs) are selectively found at the host environment interface and are capable of secreting a wide array of pharmacologically active mediators, many of which are prepackaged in granules. Over the past two decades, it has become clear that these cells have the capacity to recognize a range of infectious agents allowing them to play a key role in initiating and modulating early immune responses to infectious agents. However, a number of pathogenic and commensal microbes appear to have evolved distinct mechanisms to suppress MC mediator release to avoid elimination in the host. Understanding how these microbes suppress MC functions may have significant therapeutic value to relieve inflammatory disorders mediated by MCs.

Vaccine-mediated protection against Helicobacter pylori is not associated with increased salivary cytokine or mucin expression

BACKGROUND

The development of an effective vaccine against Helicobacter pylori is impeded by the inability to reliably produce sterilizing immunity and our lack of knowledge regarding mechanisms of protective immunity against this pathogen. It has previously been described that salivary glands are essential for vaccine-mediated protection against H. pylori, but the mechanism responsible for this effect has not been identified. In this study we tested the hypothesis that vaccines reduce H. pylori colonization by inducing an immune-mediated change in salivary gland mucin secretion.

MATERIALS AND METHODS

Sublingual and submandibular salivary glands were removed from untreated mice, from mice infected with H. pylori and from mice vaccinated against H. pylori then challenged with live bacteria. Cytokine levels in these salivary glands were quantified by ELISA, and salivary mucins were quantified by real-time PCR. Salivary antibody responses were determined by Western blot.

RESULTS

Vaccine-mediated protection against H. pylori did not produce any evidence of a positive increase in either salivary cytokine or mucin levels. In fact, many cytokines were significantly reduced in the vaccinated/challenged mice, including IL-17A, IL-10, IL-1ß, as well as the mucin Muc10. These decreases were associated with an increase in total protein content within the salivary glands of vaccinated mice which appeared to be the result of increased IgA production. While this study showed that vaccination increased salivary IgA levels, previous studies have demonstrated that antibodies do not play a critical role in protection against H. pylori that is induced by current vaccine formulations and regimes.

CONCLUSIONS

The effector mechanism of protective immunity induced by vaccination of mice did not involve immune changes within the salivary glands, nor increased production of salivary mucins.

Why can't we make an effective vaccine against Helicobacter pylori?

Helicobacter pylori is a major human pathogen that colonizes the stomach and is the lead etiological agent for several pathologies. An effective vaccine against these bacteria would be invaluable for protecting against gastric adenocarcinoma. However, the development of such a vaccine has stalled and the field has progressed little in the last decade. In this review, the authors provide an opinion on key problems that are preventing the development of a H. pylori vaccine. Primarily, this involves the inability to produce a completely protective immune response. The knock-on effects of this include a loss of industry investment. Overcoming these problems will likely involve defeating the immune-evasion defenses of H. pylori, in particular the mechanism(s) by which it evades antibody-mediated attack.

Th1-mediated immunity against Helicobacter pylori can compensate for lack of Th17 cells and can protect mice in the absence of immunization

Helicobacter pylori (H. pylori) infection can be significantly reduced by immunization in mice. Th17 cells play an essential role in the protective immune response. Th1 immunity has also been demonstrated to play a role in the protective immune response and can compensate in the absence of IL-17. To further address the potential of Th1 immunity, we investigated the efficacy of immunization in mice deficient in IL-23p19, a cytokine that promotes Th17 cell development. We also examined the course of Helicobacter infection in unimmunized mice treated with Th1 promoting cytokine IL-12. C57BL/6, IL-12 p35 KO, and IL-23 p19 KO mice were immunized and challenged with H. pylori. Protective immunity was evaluated by CFU determination and QPCR on gastric biopsies. Gastric and splenic IL-17 and IFNγ levels were determined by PCR or by ELISA. Balb/c mice were infected with H. felis and treated with IL-12 therapy and the resulting gastric bacterial load and inflammatory response were assessed by histologic evaluation. Vaccine induced reductions in bacterial load that were comparable to wild type mice were observed in both IL-12 p35 and IL-23 p19 KO mice. In the absence of IL-23 p19, IL-17 levels remained low but IFNγ levels increased significantly in both immunized challenged and unimmunized/challenged mice. Additionally, treatment of H. felis-infected Balb/c mice with IL-12 resulted in increased gastric inflammation and the eradication of bacteria in most mice. These data suggest that Th1 immunity can compensate for the lack of IL-23 mediated Th17 responses, and that protective Th1 immunity can be induced in the absence of immunization through cytokine therapy of the infected host.

Mannose receptor and macrophage galactose-type lectin are involved in Bordetella pertussis mast cell interaction

Mast cells are crucial in the development of immunity against Bordetella pertussis, and the function of TLRs in this process has been investigated. Here, the interaction between mast cells and B. pertussis with an emphasis on the role of CLRs is examined. In this study, two CLRs, MGL and MR, were detected for the first time on the surface of mast cells. The involvement of MR and MGL in the stimulation of mast cells by heat-inactivated BP was investigated by the use of blocking antibodies and specific carbohydrate ligands. The cell wall LOS of BP was also isolated to explore its role in this interaction. Mast cells stimulated with heat-inactivated BP or BP LOS induced TNF-α, IL-6, and IFN-γ secretion, which was suppressed by blocking MR or MGL. Inhibition of CLRs signaling during BP stimulation affected the ability of mast cells to promote cytokine secretion in T cells but had no effect on the cell-surface expression of ICAM1. Blocking MR or MGL suppressed BP-induced NF-κB expression but not ERK phosphorylation. Syk was involved in the CLR-mediated activation of mast cells by BP. Bacterial recognition by immune cells has been predominantly attributed to TLRs; in this study, the novel role of CLRs in the BP-mast cell interaction is highlighted.

Life in the human stomach: persistence strategies of the bacterial pathogen Helicobacter pylori

The bacterial pathogen Helicobacter pylori has co-evolved with humans and colonizes approximately 50% of the human population, but only causes overt gastric disease in a subset of infected hosts. In this Review, we discuss the pathogenesis of H. pylori and the mechanisms it uses to promote persistent colonization of the gastric mucosa, with a focus on recent insights into the role of the virulence factors vacuolating cytotoxin (VacA), cytotoxin-associated gene A (CagA) and CagL. We also describe the immunobiology of H. pylori infection and highlight how this bacterium manipulates the innate and adaptive immune systems of the host to promote its own persistence.

The role of Th cell subsets in the control of Helicobacter infections and in T cell-driven gastric immunopathology

Chronic infection with the gastric bacterial pathogen Helicobacter pylori causes gastric adenocarcinoma in a particularly susceptible fraction of the infected population. The intestinal type of gastric cancer is preceded by a series of preneoplastic lesions that are of immunopathological origin, and that can be recapitulated by experimental infection of C57BL/6 mice with Helicobacter species. Several lines of evidence suggest that specific T cell subsets and/or their signature cytokines contribute to the control of Helicobacter infections on the one hand, and to the associated gastric preneoplastic pathology on the other. Here, we have used virulent H. pylori and H. felis isolates to infect mice that lack α/β T cells due to a targeted deletion of the T cell receptor β-chain, or are deficient for the unique p35 and p19 subunits of the Th1- and Th17-polarizing cytokines interleukin (IL)-12 and IL-23, respectively. We found that α/β T cells are absolutely required for Helicobacter control and for the induction of gastric preneoplastic pathology. In contrast, neither IL-12-dependent Th1 nor IL-23-dependent Th17 cells were essential for controlling the infection; IL-12p35^-/- and IL-23p19^-/- mice did not differ significantly from wild type animals with respect to Helicobacter colonization densities. Gastritis and gastric preneoplastic pathology developed to a similar extent in all three strains upon H. felis infection; in the H. pylori infection model, IL-23p19^-/- mice exhibited significantly less gastritis and precancerous pathology. In summary, the results indicate that neither Th1 nor Th17 cells are by themselves essential for Helicobacter control; the associated gastric pathology is reduced only in the absence of Th17-polarizing IL-23, and only in the H. pylori, but not the H. felis infection model. The results thus suggest the involvement of other, as yet unknown T cell subsets in both processes.

PAR2 promotes vaccine-induced protection against Helicobacter infection in mice

BACKGROUND & AIMS

Protective immunization limits Helicobacter infection of mice by undetermined mechanisms. Protease-activated receptor 2 (PAR2) signaling is believed to regulate immune and inflammatory responses. We investigated the role of PAR2 in vaccine-induced immunity against Helicobacter infection.

METHODS

Immune responses against Helicobacter infection were compared between vaccinated PAR2-/- and wild-type (WT) mice. Bacterial persistence, gastric pathology, and inflammatory and cellular responses were assessed using the rapid urease test (RUT), histologic analyses, quantitative polymerase chain reaction, and flow cytometry, respectively.

RESULTS

Following vaccination, PAR2-/- mice did not have reductions in Helicobacter felis infection (RUT values were 0.01±0.01 for WT mice and 0.11±0.13 for PAR2-/- mice; P<.05). The vaccinated PAR2-/- mice had reduced inflammation-induced stomach tissue damage (tissue damage scores were 8.83±1.47 for WT mice and 4.86±1.35 for PAR2-/- mice; P<.002) and reduced T-helper (Th)17 responses, based on reduced urease-induced interleukin (IL)-17 secretion by stomach mononuclear cells (5182 ± 1265 pg/mL for WT mice and 350±436 pg/mL for PAR2-/- mice; P<.03) and reduced recruitment of CD4+ IL-17+ T cells into the gastric mucosa of PAR2-/- mice following bacterial challenge (3.7%±1.5% for WT mice and 2.6%±1.1% for PAR2-/- mice; P<.05). In vitro, H felis-stimulated dendritic cells (DCs) from WT mice induced greater secretion of IL-17 by ovalbumin-stimulated OT-II transgenic CD4+ T cells compared with DCs from PAR2-/- mice (4298±347 and 3230±779; P<.04), indicating that PAR2-/- DCs are impaired in priming of Th17 cells. Adoptive transfer of PAR2+/+ DCs into vaccinated PAR2-/- mice increased vaccine-induced protection (RUT values were 0.11±0.10 and 0.26±0.15 for injected and noninjected mice, respectively; P<.03).

CONCLUSIONS

PAR2 activates DCs to mediate vaccine-induced protection against Helicobacter infection in mice.

Dendritic cells prevent rather than promote immunity conferred by a helicobacter vaccine using a mycobacterial adjuvant

BACKGROUND & AIMS

Immunization against the gastric bacterium Helicobacter pylori could prevent many gastric cancers and other disorders. Most vaccination protocols used in preclinical models are not suitable for humans. New adjuvants and a better understanding of the correlates and requirements for vaccine-induced protection are needed to accelerate development of vaccines for H pylori.

METHODS

Vaccine-induced protection against H pylori infection and its local and systemic immunological correlates were assessed in animal models, using cholera toxin or CAF01 as adjuvants. The contribution of B cells, T-helper (Th)-cell subsets, and dendritic cells to H pylori-specific protection were analyzed in mice.

RESULTS

Parenteral administration of a whole-cell sonicate, combined with the mycobacterial cell-wall-derived adjuvant CAF01, protected against infection with H pylori and required cell-mediated, but not humoral, immunity. The vaccine-induced control of H pylori was accompanied by Th1 and Th17 responses in the gastric mucosa and in the gut-draining mesenteric lymph nodes; both Th subsets were required for protective immunity against H pylori. The numbers of memory CD4+ T cells and neutrophils in gastric tissue were identified as the best correlates of protection. Systemic depletion of dendritic cells or regulatory T cells during challenge infection significantly increased protection by overriding immunological tolerance mechanisms activated by live H pylori.

CONCLUSIONS

Parenteral immunization with a Helicobacter vaccine using a novel mycobacterial adjuvant induces protective immunity against H pylori that is mediated by Th1 and Th17 cells. Tolerance mechanisms mediated by dendritic cells and regulatory T cells impair H pylori clearance and must be overcome to improve immunity.

Helicobacter pylori and type 1 diabetes mellitus: possibility of modifying chronic disease susceptibility with vaccinomics at the anvil

The human gastric pathogen, Helicobacter pylori, colonizes more than 50% of the world population and is a well-known cause of peptic ulcer disease. H. pylori has been epidemiologically linked to various other diseases, among which its putative link with certain complex diseases such as type 1 diabetes mellitus (T1DM) is of interest. Although antibiotic resistance is a significant clinical problem in H. pylori infection control, the exact cause and much of the underlying mechanisms of T1DM are not clearly understood. In addition, commensal microflora, gut-adapted microbial communities, and plausible roles of some of the chronic human pathogens add an important dimension to the control of T1DM. Given this, the present review attempts to analyze and examine the confounding association of H. pylori and T1DM and the approaches to tackle them, and how the emerging field of vaccinomics might help in this pursuit.

Vaccinating against Helicobacter pylori infection

Helicobacter pylori infection of the gastric mucosa remains a cause of significant morbidity and mortality almost 30 years after its discovery. H. pylori infection can lead to several gastric maladies, including gastric cancer, and although antimicrobial therapies for the infection exist, the cost of treatment for gastric cancer and the prognosis of individuals who present with this disease make vaccine development a cost effective alternative to bacterial eradication. Experimental mucosal and systemic H. pylori vaccines in mice significantly reduce bacterial load and sometimes provide sterilizing immunity. Clinical trials of oral vaccines consisting of H. pylori proteins with bacterial exotoxin adjuvants or live attenuated bacterial vectors expressing H. pylori proteins induce adaptive immune mechanisms but fail to consistently reduce bacterial load. Clinical trials and murine studies demonstrate that where H. pylori is killed, either spontaneously or following vaccination, the host demonstrated cellular immunity. Improved efficacy of vaccines may be achieved in new trials of vaccine formulations that include multiple antigens and use methods to optimize cellular immunity. Unfortunately, the industrial sponsors that served as the primary engine for much of the previous animal and human research have withdrawn their support. A renewed or expanded commitment from the biotechnology or pharmaceutical industry that could exploit recent advances in our understanding of the host immune response to H. pylori is necessary for the advancement of an H. pylori vaccine.

New insights into the role of mast cells in autoimmunity: evidence for a common mechanism of action?

Mast cells are classically considered innate immune cells that act as first responders in many microbial infections and have long been appreciated as potent contributors to allergic reactions. However, recent advances in the realm of autoimmunity have made it clear that these cells are also involved in the pathogenic responses that exacerbate disease. In the murine models of multiple sclerosis, rheumatoid arthritis and bullous pemphigoid, both the pathogenic role of mast cells and some of their mechanisms of action are shared. Similar to their role in infection and a subset of allergic responses, mast cells are required for the efficient recruitment of neutrophils to sites of inflammation. Although this mast cell-dependent neutrophil response is protective in infection settings, it is postulated that neutrophils promote local vascular permeability and facilitate the entry of inflammatory cells that enhance tissue destruction at target sites. However, there is still much to learn. There is little information regarding mechanisms of mast cell activation in disease. Nor is it known how many mast cell-derived mediators are relevant and whether interactions with other cells are implicated in these diseases including T cells, B cells and astrocytes. Here we review the current state of knowledge about mast cells in autoimmune disease. We also discuss findings regarding newly discovered mast cell actions and factors that modulate mast cell function. We speculate that much of this new information will ultimately contribute to a greater understanding of the full range of mast cell actions in autoimmunity. This article is part of a Special Issue entitled: Mast cells in inflammation.

The effect of bacterial, viral and fungal infection on mast cell reactivity in the allergic setting

Mast cells are well known for their role in allergic inflammation where, upon aggregation of the high-affinity immunoglobulin E receptor, they release mediators such as histamine that cause classical allergic symptoms. Mast cells are located in almost all tissues and are especially numerous in organs that interface with the environment. Given this strategic location and the more recent notion that they are endowed with receptors that recognize endogenous and exogenous danger signals such as pathogens, it is not surprising that they function as important cells in immune surveillance. When mast cells are activated by pathogens they modulate innate and adaptive immune responses. In allergy, infections might cause exacerbation of the allergic reaction by affecting the reactivity of mast cells. With new developments within the field of mast cell biology, we will better understand how mast cells execute their effector functions. This knowledge will also help to improve the management of allergic diseases.

Local recall responses in the stomach involving reduced regulation and expanded help mediate vaccine-induced protection against Helicobacter pylori in mice

Helicobacter pylori is recognised as the chief cause of chronic gastritis, ulcers and gastric cancer in humans. With increased incidence of treatment failure and antibiotic resistance, development of prophylactic or therapeutic vaccination is a desirable alternative. Although the results of vaccination studies in animal models have been promising, studies in human volunteers have revealed problems such as 'post-immunisation gastritis' and comparatively poor responses to vaccine antigens. The focus of this study was to compare the gastric and systemic cellular immune responses induced by recombinant attenuated Salmonella Typhimurium-based vaccination in the C57BL/6 model of H. pylori infection. Analysis of lymphocyte populations in the gastric mucosa, blood, spleen, paragastric LN and MLN revealed that the effects of vaccination were largely confined to the parenchymal stomach rather than lymphoid organs. Vaccine-induced protection was correlated with an augmented local recall response in the gastric mucosa, with increased proportions of CD4(+) T cells, neutrophils and reduced proportions of CD4(+) Treg. CD4(+) T cells isolated from the stomachs of vaccinated mice proliferated ex vivo in response to H. pylori antigen, and secreted Th1 cytokines, particularly IFN-γ. This detailed analysis of local gastric immune responses provides insight into the mechanism of vaccine-induced protection.

Helicobacter pylori and its effect on innate and adaptive immunity: new insights and vaccination strategies

Infection with the gastric bacterium Helicobacter pylori invariably leads to active chronic gastritis, and is strongly correlated to peptic ulcer disease, gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma. The infection leads to local accumulation of inflammatory cells and strong activation of B- and T-cell immunity. Still, the immune response can not eliminate the bacteria, and unless antibiotic treatment is used, the infection is usually lifelong. During the last few years, several immunomodulatory properties of H. pylori have been described, which probably contribute to the inability of the immune system to eradicate the bacterium. Another factor promoting bacterial persistence is probably the induction of a substantial regulatory T-cell response by the infection. Several different immunization schedules have resulted in protective immunity in animal models, while in humans no reliable vaccine is available as yet. In this article, we describe the innate and adaptive immune responses to H. pylori, and the attempts to create an effective vaccine.

Dermal mast cells reduce progressive tissue necrosis caused by subcutaneous infection with Streptococcus pyogenes in mice

A single subcutaneous (s.c.) infection with 1×10(7) c.f.u. GAS472, a group A streptococcus (GAS) serotype M1 strain isolated from the blood of a patient suffering from streptococcal toxic shock syndrome, led to severe damage of striated muscle layers in the feet of mast cell (MC)-deficient WBB6F(1)-Kit(W)/Kit(W-v) (W/W(v)) mice 72&emsp14;h after infection. In contrast, no damage was recognized in striated muscle layers in the feet of the control WBB6F(1)-Kit(+/+) (+/+) mice 72&emsp14;h after infection. In addition, adoptively transferred MCs reduced progressive tissue necrosis of the feet of W/W(v) mice after infection. However, there was no significant difference in the mortality rates between the W/W(v) and +/+ mice, or between the human CD46-expressing transgenic (Tg) mouse bone marrow-derived cultured MC-reconstituted W/W(v) and non-Tg mouse bone marrow-derived cultured MC-reconstituted W/W(v) mice after infection. Consequently, although MCs can help to reduce the severity of necrosis of the feet caused by s.c. infection with GAS472, such reduction of tissue necrosis scarcely improves the mortality rates of these mice. Moreover, human CD46 does not play a crucial role in the MC-mediated innate immune defence against GAS infection.

Inflammation, immunity, and vaccines for Helicobacter

Helicobacter pylori represents the major etiologic agent of gastritis, gastric, and duodenal ulcer disease and can cause gastric cancer and mucosa-associated lymphoid tissue B-cell lymphoma. It is clear that the consequences of infection reflect diverse outcomes of the interaction of bacteria and host immune system. The hope is that by deciphering the deterministic rules--if any--of this interplay, we will eventually be able to predict, treat, and ultimately prevent disease. Over the past year, research on the immunology of this infection started to probe the role of small noncoding RNAs, a novel class of immune response regulators. Furthermore, we learned new details on how infection is detected by innate pattern recognition receptors. Induction of effective cell-mediated immunity will be key for the development of a vaccine, and new work published analyzed the relevance and contribution of CD4 T helper cell subsets to the immune reaction. Th17 cells, which are also induced during natural infection, were shown to be particularly important for vaccination. Cost-efficiency of vaccination was re-assessed and confirmed. Thus, induction and shaping of the effector roles of such protective Th populations will be a target of the newly described vaccine antigens, formulations, and modes of application that we also review here.

The chemokine receptor CXCR5 is pivotal for ectopic mucosa-associated lymphoid tissue neogenesis in chronic Helicobacter pylori-induced inflammation

Ectopic lymphoid follicles are a key feature of chronic inflammatory autoimmune and infectious diseases, such as rheumatoid arthritis, Sjögren's syndrome, and Helicobacter pylori-induced gastritis. Homeostatic chemokines are considered to be involved in the formation of such tertiary lymphoid tissue. High expression of CXCL13 and its receptor, CXCR5, has been associated with the formation of ectopic lymphoid follicles in chronic infectious diseases. Here, we defined the role of CXCR5 in the development of mucosal tertiary lymphoid tissue and gastric inflammation in a mouse model of chronic H. pylori infection. CXCR5-deficient mice failed to develop organized gastric lymphoid follicles despite similar bacterial colonization density as infected wild-type mice. CXCR5 deficiency altered Th17 responses but not Th1-type cellular immune responses to H. pylori infection. Furthermore, CXCR5-deficient mice exhibited lower H. pylori-specific serum IgG and IgA levels and an overall decrease in chronic gastric immune responses. In conclusion, the development of mucosal tertiary ectopic follicles during chronic H. pylori infection is strongly dependent on the CXCL13/CXCR5 signaling axis, and lack of de novo lymphoid tissue formation attenuates chronic immune responses.

Advances in vaccination against Helicobacter pylori

A vaccination against Helicobacter pylori may represent both prophylactic and therapeutic approaches to the control of H. pylori infection. Different protective H. pylori-derived antigens, such as urease, vacuolating cytotoxin A, cytotoxin-associated antigen, neutrophil-activating protein and others can be produced at low cost in prokaryote expression systems and most of these antigens have already been administered to humans and shown to be safe. The recent development by Graham et al. of the model of H. pylori challenge in humans, the recent published clinical trials and the last insight generated in animal models of H. pylori infection regarding the immune mechanisms leading to vaccine-induced Helicobacter clearance will facilitate the evaluation of immunogenicity and efficacy of H. pylori vaccine candidates in Phase II and III clinical trials.

Infection of mast cells with live streptococci causes a toll-like receptor 2- and cell-cell contact-dependent cytokine and chemokine response

Mast cells (MCs) are strongly implicated in immunity toward bacterial infection, but the molecular mechanisms by which MCs contribute to the host response are only partially understood. We addressed this issue by examining the direct effects of a Gram-positive pathogen, Streptococcus equi, on bone marrow-derived MCs (BMMCs). Ultrastructural analysis revealed extensive formation of dilated rough endoplasmic reticulum in response to bacterial infection, indicating strong induction of protein synthesis. However, the BMMCs did not show signs of extensive degranulation, and this was supported by only slow release of histamine in response to infection. Coculture of live bacteria with BMMCs caused a profound secretion of CCL2/MCP-1, CCL7/MCP-3, CXCL2/MIP-2, CCL5/RANTES, interleukin-4 (IL-4), IL-6, IL-12, IL-13, and tumor necrosis factor alpha, as shown by antibody-based cytokine/chemokine arrays and/or enzyme-linked immunosorbent assay. In contrast, heat-inactivated bacteria caused only minimal cytokine/chemokine release. The cytokine/chemokine responses were substantially attenuated in Toll-like receptor 2-deficient BMMCs and were strongly dependent on cell-cell contacts between bacteria and BMMCs. Gene chip microarray analysis confirmed a massively upregulated expression of the genes coding for the secreted cytokines and chemokines and also identified a pronounced upregulation of numerous additional genes, including transcription factors, signaling molecules, and proteases. Together, the present study outlines MC-dependent molecular events associated with Gram-positive infection and thus provides an advancement in our understanding of how MCs may contribute to host defense toward bacterial insults.

Partial protection against Helicobacter pylori in the absence of mast cells in mice

The goal of this study is to evaluate the contribution of mast cells to Helicobacter pylori immunity in a model of vaccine-induced protection. Mast cell-deficient Kitl(Sl)/Kitl(Sl-d) and control mice were immunized with H. pylori sonicate plus cholera toxin and challenged with H. pylori, and the bacterial loads, inflammatory infiltrates, and cytokine responses were evaluated and compared at 1, 2, and 4 weeks postchallenge. In vitro stimulation assays were performed using bone marrow-derived mast cells, and recall assays were performed with spleen cells of immunized mast cell-deficient and wild-type mice. Bacterial clearance was observed by 2 weeks postchallenge in mast cell-deficient mice. The bacterial load was reduced by 4.0 log CFU in wild-type mice and by 1.5 log CFU in mast cell-deficient mice. Neutrophil numbers in the gastric mucosa of immune Kitl(Sl)/Kitl(Sl-d) mice were lower than those for immune wild-type mice (P < 0.05). Levels of gastric interleukin-17 (IL-17) and tumor necrosis factor alpha (TNF-alpha) were also significantly lower in immune Kitl(Sl)/Kitl(Sl-d) mice than in wild-type mice (P < 0.001). Immunized mast cell-deficient and wild-type mouse spleen cells produced IFN-gamma and IL-17 in response to H. pylori antigen stimulation. TNF-alpha and CXC chemokines were detected in mast cell supernatants after 24 h of stimulation with H. pylori antigen. The results indicate that mast cells are not essential for but do contribute to vaccine-induced immunity and that mast cells contribute to neutrophil recruitment and inflammation in response to H. pylori.

The CD4+ T cell-mediated IFN-gamma response to Helicobacter infection is essential for clearance and determines gastric cancer risk

Chronic infection with the bacterial pathogen Helicobacter pylori is a risk factor for the development of gastric cancer, yet remains asymptomatic in the majority of individuals. We report here that the C57BL/6 mouse model of experimental infection with the closely related Helicobacter felis recapitulates this wide range in host susceptibility. Although the majority of infected animals develop premalignant lesions such as gastric atrophy, compensatory epithelial hyperplasia, and intestinal metaplasia, a subset of mice is completely protected from preneoplasia. Protection is associated with a failure to mount an IFN-gamma response to the infection and with a concomitant high Helicobacter burden. Using a vaccine model as well as primary infection and adoptive transfer models, we demonstrate that IFN-gamma, secreted predominantly by CD4(+)CD25(-) effector T(H) cells, is essential for Helicobacter clearance, but at the same time mediates the formation of preneoplastic lesions. We further provide evidence that IFN-gamma triggers a common transcriptional program in murine gastric epithelial cells in vitro and in vivo and induces their preferential transformation to the hyperplastic phenotype. In summary, our data suggest a dual role for IFN-gamma in Helicobacter pathogenesis that could be the basis for the differential susceptibility to H. pylori-induced gastric pathology in the human population.

Lactobacillus salivarius modulates cytokine induction and virulence factor gene expression in Helicobacter pylori

Human infection by the gastric pathogen Helicobacter pylori is characterized by a robust immune response which rarely prevents persistent H. pylori colonization. Emerging evidence suggests that lactobacilli may reduce H. pylori infection rates and associated inflammation. In this study, we measured the ability of two model strains of Lactobacillus salivarius (UCC118 and UCC119) to modulate gastric epithelial cell chemokine responses to H. pylori infection. Pre-treatment of AGS cells with either L. salivarius strain significantly decreased interleukin-8 (IL-8) production upon exposure to H. pylori, but not in cells stimulated with TNF-alpha. The production of the chemokines CCL20 and IP-10 by AGS cells infected with H. pylori was also altered following pre-treatment with UCC118 and UCC119. We showed that a greater reduction in IL-8 production with UCC119 was due to the production of more acid by this strain. Furthermore, UV-killed cells of both lactobacillus strains were still able to reduce H. pylori-induced IL-8 in the absence of acid production, indicating the action of a second anti-inflammatory mechanism. This immunomodulatory activity was not dependent on adhesion to epithelial cells or bacteriocin production. Real-time RT-PCR analysis showed that expression of eight of twelve Cag pathogenicity island genes tested was downregulated by exposure to L. salivarius, but not by cells of four other lactobacillus species. CagA accumulated in H. pylori cells following exposure to L. salivarius presumably as a result of loss of functionality of the Cag secretion system. These data identified a new mechanism whereby some probiotic bacteria have a positive effect on H. pylori-associated inflammation without clearing the infection.