Helicobacter pylori stimulates dendritic cells to induce interleukin-17 expression from CD4+ T lymphocytes. Infect Immun. 2010;78:845-853. [PMID: 19917709 DOI: 10.1128/iai.00524-09]

Th1 and Th17 responses to Helicobacter pylori in Bangladeshi infants, children and adults

Both Th1 and Th17 cells are important components of the immune response to Helicobacter pylori (Hp) in adults, but less is known about T cell responses to Hp during early childhood, when the infection is often acquired. We investigated Th1 and Th17 type responses to Hp in adults, children and infants in Bangladesh, where Hp is highly endemic. IL-17 and IFN-γ mRNA levels in gastric biopsies from Hp-infected Bangladeshi adults were analyzed and compared to levels in infected and uninfected Swedish controls. Since biopsies could not be collected from infants and children, cytokine responses in Bangladeshi infants (6-12 months), children (3-5 years) and adults (>19 years) were instead compared by stimulating peripheral blood mononuclear cells (PBMCs) with a Hp membrane preparation (MP) and analyzing culture supernatants by ELISA and cytometric bead array. We found significantly higher expression of IL-17 and IFN-γ mRNA in gastric mucosa of Hp-infected Bangladeshi and Swedish adults compared to uninfected Swedish controls. PBMCs from all age groups produced IL-17 and IFN-γ after MP stimulation, but little Th2 cytokines. IL-17 and IFN-γ were primarily produced by CD4+ T cells, since CD4+ T cell depleted PBMCs produced reduced amounts of these cytokines. Infant cells produced significantly more IL-17, but similar levels of IFN-γ, compared to adult cells after MP stimulation. In contrast, polyclonal stimulation induced lower levels IL-17 and IFN-γ in infant compared to adult PBMCs and CD4+ T cells. The strong IL-17 production in infants after MP stimulation was paralleled by significantly higher production of the IL-17 promoting cytokine IL-1β from infant compared to adult PBMCs and monocytes. In conclusion, these results show that T cells can produce high levels of IL-17 and IFN-γ in response to Hp from an early age and indicate a potential role for IL-1β in promoting Th17 responses to Hp during infancy.

Role of Treg and TH17 cells of the gastric mucosa in children with Helicobacter pylori gastritis

OBJECTIVE

The aim of the present study was to examine the expression of FOXP3, interleukin (IL)-10, transforming growth factor (TGF)-β1, IL-17A, and T helper 17 (TH17) cells/FOXP3+ regulatory T (Treg) cells balance in the gastric mucosa of children with Helicobacter pylori infection, in relation to the gastric histopathology.

METHODS

Antral mucosal biopsies were obtained from 20 children with H pylori(+) gastritis and 20 age- and sex-matched normal controls. Histopathology was assessed by the updated Sydney classification. Gene expression of FOXP3, IL-10, and TGF-β1 was analyzed by quantitative real-time polymerase chain reaction. Immunohistochemical staining for FOXP3+ Treg and TH17 cells was performed.

RESULTS

The gene expression levels of FOXP3, TGF-β1, and IL-10 messenger RNA (mRNA) and the number of FOXP3+ Treg were significantly higher in the H pylori(+) gastritis group than in the control group (P < 0.01). FOXP3 mRNA levels were correlated positively with TGF-β1 and IL-10 mRNA levels in the H pylori(+) gastritis group (P < 0.05). Furthermore, FOXP3 mRNA levels were correlated positively with the bacterial density, infiltration of polymorphonuclear cells, and mononuclear cells in the H pylori(+) gastritis group (P < 0.05). The number of TH17 cells was significantly higher in the H pylori(+) gastritis group than in the control group (P < 0.05). In addition, the number of TH17 cells was correlated negatively with the bacterial density and positively with the inflammatory scores of polymorphonuclear cells and mononuclear cells in the H pylori(+) gastritis group (P < 0.05). A negative correlation between the TH17 cells/FOXP3+ Treg ratio and the bacterial density was demonstrated in the H pylori(+) gastritis group (P < 0.05).

CONCLUSIONS

This study suggested that a TH17/Treg balance toward a Treg-biased response favors the persistence of bacteria, causing chronic active gastritis.

Role of childhood infection in the sequelae of H. pylori disease

The persistence of Helicobacter pylori infection plays a fundamental role in the development of H. pylori-associated complications. Since the majority of infected persons acquire the bacteria during early childhood, an examination of the immunobiology of H. pylori infection in children compared with that of adults may help identify host factors that contribute to persistent infection. Therefore, we begin our review of the role of persistence in H. pylori disease with an assessment of the clinical features of H. pylori infection in children. We next review the bacterial factors that promote colonization and evasion of host defense mechanisms. We then focus our attention on the early host immunological factors that promote persistence of the infection and its complications in humans and mouse models. We also highlight topics in which further research is needed. An examination of how immunological factors cause divergent manifestations of H. pylori infection in children compared with adults may provide new insight for therapeutic modification or prevention of persistent H. pylori infection and its complications.

High levels of FOXP3⁺ regulatory T cells in gastric MALT lymphoma predict responsiveness to Helicobacter pylori eradication

BACKGROUND

Although Helicobacter pylori eradication is a first-line treatment of gastric MALT lymphoma, roughly 25% of patients do not respond to treatment. CD4⁺ FOXP3⁺ regulatory T (Treg) cells regulate immune responses in physiological conditions and various inflammatory conditions, including H. pylori-associated diseases. Our goal was to determine how Treg cells affect responsiveness to H. pylori eradication therapy.

MATERIALS AND METHODS

We performed dual immunohistochemistry for CD4 and FOXP3 to evaluate the prevalence of FOXP3⁺ Treg cells in the stomach of 63 patients with MALT lymphoma and 55 patients with chronic active gastritis. Receiver operating characteristic analysis was carried out to determine the best cut-off point in differentiating H. pylori eradication responders from nonresponders.

RESULTS

Both the FOXP3⁺/CD4⁺ cell ratio and the absolute number of FOXP3⁺ cells per high-power field in MALT lymphoma were significantly greater in H. pylori eradication responders compared with nonresponders, suggesting that Treg cells function in regression mechanisms of MALT lymphomas. Cut-off points with good sensitivities and specificities were obtained to predict eradication outcome.

CONCLUSIONS

A high number of Treg cells or a high ratio of Treg cells to the total number of CD4⁺ T cells in gastric MALT lymphoma could predict responsiveness to eradication therapy.

Inflammatory cytokine and microRNA responses of primary human dendritic cells cultured with Helicobacter pylori strains

Primary human dendritic cells (DC) were used to explore the inflammatory effectors, including cytokines and microRNAs, regulated by Helicobacter pylori. In a 48 h ex-vivo co-culture system, both H. pylori B38 and B45 strains activated human DCs and promoted a strong inflammatory response characterized by the early production of pro-inflammatory TNFα and IL-6 cytokines, followed by IL-10, IL-1β, and IL-23 secretion. IL-23 was the only cytokine dependent on the cag pathogenicity island status of the bacterial strains. DC activation and cytokine production were accompanied by an early miR-146a upregulation followed by a strong miR-155 induction, which mainly controlled TNFα production. These results pave the way for further investigations into the nature of H. pylori antigens and the subsequently activated signaling pathways involved in the inflammatory response to H. pylori infection, the deregulation of which may likely contribute to gastric lymphomagenesis.

DC-LAMP+ dendritic cells are recruited to gastric lymphoid follicles in Helicobacter pylori-infected individuals

Infection with Helicobacter pylori is associated with development of ulcer disease and gastrointestinal adenocarcinoma. The infection leads to a large infiltration of immune cells and the formation of organized lymphoid follicles in the human gastric mucosa. Still, the immune system fails to eradicate the bacteria, and the substantial regulatory T cell (Treg) response elicited is probably a major factor permitting bacterial persistence. Dendritic cells (DCs) are professional antigen-presenting cells that can activate naive T cells, and maturation of DCs is crucial for the initiation of primary immune responses. The aim of this study was to investigate the presence and localization of mature human DCs in H. pylori-infected gastric mucosa. Gastric antral biopsy specimens were collected from patients with H. pylori-associated gastritis and healthy volunteers, and antrum tissue was collected from patients undergoing gastric resection. Immunohistochemistry and flow cytometry showed that DCs expressing the maturation marker dendritic cell lysosome-associated membrane glycoprotein (DC-LAMP; CD208) are enriched in the H. pylori-infected gastric mucosa and that these DCs are specifically localized within or close to lymphoid follicles. Gastric DC-LAMP-positive (DC-LAMP(+)) DCs express CD11c and high levels of HLA-DR but little CD80, CD83, and CD86. Furthermore, immunofluorescence analyses demonstrated that DC-LAMP(+) DCs are in the same location as FoxP3-positive putative Tregs in the follicles. In conclusion, we show that DC-LAMP(+) DCs with low costimulatory capacity accumulate in the lymphoid follicles in human H. pylori-infected gastric tissue, and our results suggest that Treg-DC interactions may promote chronic infection by rendering gastric DCs tolerogenic.

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.

Helicobacter pylori infection and lung cancer: a review of an emerging hypothesis

Helicobacter pylori (Hp) is one of the most common bacteria infecting humans. Recently, certain extragastric manifestations, linked to Hp infection, have been widely investigated, suggesting that Hp infection might be a 'systemic' disease. Accumulating, yet limited, evidence points to a potential association between Hp infection and lung cancer risk. Epidemiologic studies have shown that odds ratios (estimated relative risks) of lung cancer with Hp infection range from 1.24 to 17.78 compared with the controls, suggesting an increased lung cancer risk in the population exposed to Hp infection although far from supporting a causal relationship between Hp and lung cancer. Many studies have demonstrated the existence of Hp in the mucosa of the upper respiratory tract with no direct evidence of Hp-localization in lung tissue in the published literatures, rendering the possible functional mechanism underlying the association an open question. We followed the classic hypothesis-generating path, where we have thoroughly reviewed the publications on lung cancer and Hp infection from serological association to possible mechanisms as: (i) p130cas activated by Src kinase following Hp-host communication and p130cas-related carcinogenesis as in various malignancies; and (ii) gastroesophageal reflux and inhalation of urease or gastrin, which are Hp-related carcinogenic factors and present in lung tissues. We propose rigorous investigations regarding the Hp-lung cancer association and, if confirmed, the mechanisms of Hp infection leading to lung cancer development and progression. Clarification on Hp-lung cancer association is important for the understanding of lung cancer beyond tobacco-smoking-related carcinogenesis.

Helicobacter, Inflammation, and Gastric Cancer

Helicobacter pylori infection leads to long-lasting chronic inflammation and represents the most common risk factor underlying gastric cancer. Recently, new insights into the mechanisms through which H. pylori and mucosal inflammation lead to cancer development have emerged. H. pylori virulence factors, in particular specific CagA genotypes, represent main factors in gastric cancer, inducing altered intracellular signaling in epithelial cells. The chronic nature of H. pylori infection appears to relate to the VacA virulence factor and Th17/Treg mechanisms. A role of H. pylori infection in epigenetic and microRNA deregulation has been shown. Mutation of the epithelial cell genome, a hallmark of cancer, was demonstrated to accumulate in H. pylori infected stomach partly due to inadequate DNA repair. Gastric stem cells were shown to be targets of oxidative injury in the Helicobacter-inflammatory milieu. Recent advances emphasizing the contribution of bacterial factors, inflammatory mediators, and the host epithelial response in gastric carcinogenesis are reviewed.

Stromal cells induce Th17 during Helicobacter pylori infection and in the gastric tumor microenvironment

Gastric cancer is associated with chronic inflammation and Helicobacter pylori infection. Th17 cells are CD4(+) T cells associated with infections and inflammation; but their role and mechanism of induction during carcinogenesis is not understood. Gastric myofibroblasts/fibroblasts (GMF) are abundant class II MHC expressing cells that act as novel antigen presenting cells. Here we have demonstrated the accumulation of Th17 in H. pylori-infected human tissues and in the gastric tumor microenvironment. GMF isolated from human gastric cancer and H. pylori infected tissues co-cultured with CD4(+) T cells induced substantially higher levels of Th17 than GMF from normal tissues in an IL-6, TGF-β, and IL-21 dependent manner. Th17 required interaction with class II MHC on GMF for activation and proliferation. These studies suggest that Th17 are induced during both H. pylori infection and gastric cancer in the inflammatory milieu of gastric stroma and may be an important link between inflammation and carcinogenesis.

Dendritic cell function in the host response to Helicobacter pylori infection of the gastric mucosa

Dendritic cells (DCs) play an important role as antigen-presenting cells that direct the nature of the adaptive immune response. Subtypes are differentiated by lineage, tissue, marker expression and function. Their function in promoting regulatory T cells in the gut to maintain immunologic homeostasis is well documented, but their role in the Helicobacter pylori-infected stomach is less clear. Some analyses of bone marrow-derived DCs stimulated with H. pylori have demonstrated proinflammatory potential based on secretion of IL-12 or IL-23 or activation of Th1 and Th17 cells. Other analyses indicate that H. pylori-activated DCs are less responsive compared with other gastrointestinal bacteria and activate DCs to promote Treg development. DC depletion in mice supports a role for DCs in down-regulating H. pylori-induced gastritis. These data indicate that gastric DCs recognize H. pylori much like DCs in the gut that recognize commensal organisms and promote a regulatory T-cell response. This is consistent with a growing body of literature documenting the prevalence and function of Treg cells in the host response to H. pylori. Research is now focused on characterizing how H. pylori induces such activity in DCs and identifying the mechanisms by which H. pylori-activated DCs activate Treg cells.

Helicobacter pylori induces in-vivo expansion of human regulatory T cells through stimulating interleukin-1β production by dendritic cells

Helicobacter pylori is one of the most common infections in the world. Despite inciting inflammation, immunological clearance of the pathogen is often incomplete. CD4(+) CD25(hi) forkhead box protein 3 (FoxP3(+)) regulatory T cells (T(regs)) are potent suppressors of different types of immune responses and have been implicated in limiting inflammatory responses to H. pylori. Investigating the influence of H. pylori on T(reg) function and proliferation, we found that H. pylori-stimulated dendritic cells (DCs) induced proliferation in T(regs) and impaired their suppressive capability. This effect was mediated by interleukin (IL)-1β produced by H. pylori-stimulated DCs. These data correlated with in-vivo observations in which H. pylori(+) gastric mucosa contained more T(regs) in active cell division than uninfected stomachs. Inciting local proliferation of T(regs) and inhibiting their suppressive function may represent a mechanism for the chronic gastritis and carcinogenesis attributable to H. pylori.

Comparative analysis of the interaction of Helicobacter pylori with human dendritic cells, macrophages, and monocytes

Helicobacter pylori may cause chronic gastritis, gastric cancer, or lymphoma. Myeloid antigen-presenting cells (APCs) are most likely involved in the induction and expression of the underlying inflammatory responses. To study the interaction of human APC subsets with H. pylori, we infected monocytes, monocyte-derived dendritic cells (DCs), and monocyte-derived (classically activated; M1) macrophages with H. pylori and analyzed phenotypic alterations, cytokine secretion, phagocytosis, and immunostimulation. Since we detected CD163(+) (alternatively activated; M2) macrophages in gastric biopsy specimens from H. pylori-positive patients, we also included monocyte-derived M2 macrophages in the study. Upon H. pylori infection, monocytes secreted interleukin-1β (IL-1β), IL-6, IL-10, and IL-12p40 (partially secreted as IL-23) but not IL-12p70. Infected DCs became activated, as shown by the enhanced expression of CD25, CD80, CD83, PDL-1, and CCR7, and secreted IL-1β, IL-6, IL-10, IL-12p40, IL-12p70, and IL-23. However, infection led to significantly downregulated CD209 and suppressed the constitutive secretion of macrophage migration inhibitory factor (MIF). H. pylori-infected M1 macrophages upregulated CD14 and CD32, downregulated CD11b and HLA-DR, and secreted mainly IL-1β, IL-6, IL-10, IL-12p40, and IL-23. Activation of DCs and M1 macrophages correlated with increased capacity to induce T-cell proliferation and decreased phagocytosis of dextran. M2 macrophages upregulated CD14 and CD206 and secreted IL-10 but produced less of the proinflammatory cytokines than M1 macrophages. Thus, H. pylori affects the functions of human APC subsets differently, which may influence the course and the outcome of H. pylori infection. The suppression of MIF in DCs constitutes a novel immune evasion mechanism exploited by H. pylori.

Targeting STAT3 in gastric cancer

INTRODUCTION

STAT3 is a key transcription factor for many regulatory factors that modulate gene transcription. Particularly important are cytokines and growth factors that maintain homeostasis by regulating immunocytes, stromal and epithelial cells. Dysregulation of STAT3 by constitutive activation plays an important role in the initiation of inflammation and cellular transformation in numerous cancers, especially of epithelial origin. This review focuses on STAT3 drive in gastric cancer initiation and progression, with emphasis on its activation by cytokines, and how targeting the primary drivers or gastric STAT3 therapeutically may prevent or slow stomach cancer development.

AREAS COVERED

This review will discuss the mechanics of STAT3 signalling, how constitutive STAT3 activation promotes gastric tumourigenesis in both human adenocarcinomas and mouse models, the nature of the upstream regulators of STAT3, and their association with chronic Helicobacter pylori infection, STAT3-activated genes that promote transformation and progression, and finally the development and use of STAT3 and upstream cytokine inhibitors as therapeutics.

EXPERT OPINION

Chronic STAT3 activation is a key event in gastric cancer induction and progression. Specific targeting of stomach epithelial STAT3 or blocking IL-11Rα/gp130 and/or EGFR signal transduction in chronic gastric inflammation and metaplasia may be therapeutically effective in preventing gastric carcinogenesis.

A role for altered phagosome maturation in the long-term persistence of Helicobacter pylori infection

The vigorous host immune response that is mounted against Helicobacter pylori is unable to eliminate this pathogenic bacterium from its niche in the human gastric mucosa. This results in chronic inflammation, which can develop into gastric or duodenal ulcers in 10% of infected individuals and gastric cancer in 1% of infections. The determinants for these more severe pathologies include host (e.g., high IL-1β expression polymorphisms), bacterial [e.g., cytotoxicity-associated gene (cag) pathogenicity island], and environmental (e.g., dietary nitrites) factors. However, it is the failure of host immune effector cells to eliminate H. pylori that underlies its persistence and the subsequent H. pylori-associated disease. Here we discuss the mechanisms used by H. pylori to survive the host immune response and, in particular, the role played by altered phagosome maturation.

Serologic evidence that ascaris and toxoplasma infections impact inflammatory responses to Helicobacter pylori in Colombians

BACKGROUND

Helicobacter pylori-infected children from coastal Tumaco, Colombia, have more parasitism, and adults have lower gastric cancer risk compared with high-altitude Pasto/Tuquerres residents. Because helminth and Toxoplasma gondii infections alter helicobacter gastritis in rodent models, we determined whether seropositivity to Ascaris lumbricoides or T. gondii was associated with Th2-IgG1 or Th1-IgG2 responses to H. pylori.

METHODS

Sera (240) from the two populations were evaluated for A. lumbricoides and T. gondii seropositivity and results correlated with IgE and IgG isotype responses to H. pylori.

RESULTS

Most Tumaco children and adults were seropositive for A. lumbricoides (89%, 66%), T. gondii (59%, 98%), or both (45%, 66%). In contrast, seropositivity among Pasto/Tuquerres children was much lower (9%A. lumbricoides, 11%T. gondii, and 2% dual positive) but increased in adults (58%A. lumbricoides, 82%T. gondii, and 41% dual positive). A. lumbricoides seropositivity correlated with elevated IgE and anti-inflammatory Th2-IgG1 responses to H. pylori, while T. gondiigondii seropositivity was linked to elevated IgE, pro-inflammatory Th1-IgG2, IgG3, and IgG4 responses to H. pylori. Individuals with high T. gondii titers had reduced Th1-IgG2, IgG3, and IgG4 responses to H. pylori.

CONCLUSIONS

Results support regional differences for childhood parasitism and indicate A. lumbricoides and T. gondii infections may impact inflammatory responses to H. pylori and partially explain differences in gastric cancer risk in Colombia.

Bacterial chemotaxis modulates host cell apoptosis to establish a T-helper cell, type 17 (Th17)-dominant immune response in Helicobacter pylori infection

The host inflammatory response to chronic bacterial infections often dictates the disease outcome. In the case of the gastric pathogen Helicobacter pylori, host inflammatory responses result in outcomes that range from moderate and asymptomatic to more severe with concomitant ulcer or cancers. It was found recently that H. pylori chemotaxis mutants (Che(-)), which lack directed motility but colonize to nearly wild-type levels, trigger less host inflammation. We used these mutants to observe host immune responses that resulted in reduced disease states. Here we report that these mutants are defective for early gastric recruitment of CD4(+) T cells compared with wild-type infection. Furthermore, Che(-) mutant infections lack the T-helper cell, type 17 (Th17) component of the immune response, as measured by cytokine mRNA levels in gastric tissue via intracellular cytokine staining and immunofluorescence. We additionally find that a Che(-) mutant infection results in significantly less host cell apoptosis than does wild-type infection, in accordance with previous observations that T-helper cell, type 17 responses in Citrobacter rodentium infections are driven by concomitant bacterial and apoptotic cell signals. We propose that bacterial chemotaxis allows H. pylori to access a particular host niche that allows the bacteria to express or deliver proapoptotic host cell factors. This report indicates that chemotaxis plays a role in enhancing apoptosis, suggesting bacterial chemotaxis systems might serve as therapeutic targets for infections whose symptoms arise from host cell apoptosis and tissue damage.

Vaccine-induced immunity against Helicobacter pylori in the absence of IL-17A

BACKGROUND

  Helicobacter pylori (H. pylori) is a gram negative bacterium that can cause diseases such as peptic ulcers and gastric cancer. IL-17A, a proinflammatory cytokine that can induce the production of CXC chemokines for neutrophil recruitment, has recently been shown to be elevated in both H. pylori-infected patients and mice. Furthermore, studies in mouse models of vaccination have reported levels significantly increased over infected, unimmunized mice and blocking of IL-17A during the challenge phase in immunized mice reduces protective immunity. Because many aspects of immunity had redundant or compensatory mechanisms, we investigated whether mice could be protectively immunized when IL-17A function is absent during the entire immune response using IL-17A and IL-17A receptor knockout (KO) mice immunized against H. pylori.

MATERIALS AND METHODS

  Gastric biopsies were harvested from naïve, unimmunized/challenged, and immunized/challenged wild type (WT) and KO mice and analyzed for inflammation, neutrophil, and bacterial levels. Groups of IL-17A KO mice were also treated with anti-IFNγ or control antibodies.

RESULTS

  Surprisingly, all groups of immunized KO mice reduced their bacterial loads comparably to WT mice. The gastric neutrophil counts did not vary significantly between IL-17A KO and WT mice, whereas IL-17RA KO mice had on average a four-fold decrease compared to WT. Additionally, we performed an immunization study with CXCR2 KO mice and observed significant gastric neutrophils and reduction in bacterial load.

CONCLUSION

  These data suggest that there are compensatory mechanisms for protection against H. pylori and for neutrophil recruitment in the absence of an IL-17A-CXC chemokine pathway.

The role of interleukin-17 in the Helicobacter pylori induced infection and immunity

BACKGROUND

Helicobacter pylori infection is regarded as the major cause of various gastric diseases and induces the production of several cytokines including interleukin-17 (IL-17) recently recognized as an important player in the mammalian immune system.

OBJECTIVE

This review deals with the role of IL-17 on the H. pylori-induced infection and immunity in humans and experimental animals.

RESULTS

H. pylori infection increases IL-17 in the gastric mucosa of humans and experimental animals. In humans, IL-17 induces the secretion of IL-8 by activating the ERK 1/2 MAP kinase pathway and the released IL-8 attracts neutrophils promoting inflammation. IL-23 is increased in patients with H. pylori-related gastritis and regulates IL-17 secretion via STAT3 pathway. Studies in H. pylori-infected mice indicate that IL-17 is primarily associated with gastric inflammation. The early events in the immune response of immunized and challenged mice include the recruitment of T cells and the production of IL-17. Neutrophil attracting chemokines are released, and the bacterial load is considerably reduced. IL-17 plays a dual role in infection and vaccination. In infection, T regulatory cells (Tregs) suppress the inflammatory reaction driven by IL-17 thereby favoring bacterial persistence. Immunization produces Helicobacter-specific memory T-helper cells that can possibly alter the ratio between T-helper 17 and Treg responses so that the IL-17-driven inflammatory reaction can overcome the Treg response leading to bacterial clearance.

CONCLUSION

IL-17 plays an important role in H. pylori-related gastritis and in the reduction of Helicobacter infection in mice following immunization.

IL-17A and IL-17F gene expression is strongly induced in the mucosa of H. pylori-infected subjects from Kenya and Germany

Helicobacter pylori infection is the major cause of gastritis. Immunologically, H. pylori gastritis is associated with an infiltration of immune cells into gastric mucosa and the upregulation of various cytokines. Here, we analysed the gene expression of IL-1- and IL-17-related cytokines in regard to H. pylori infection in 85 German and 51 Kenyan patients with reflux-related or dyspeptic symptoms, respectively. Degree of gastritis and density of colonization were assessed histologically in accordance with the updated Sydney classification. Gene expression levels of cytokines IL-1β, IL-8, IL-18, IL-33, IL-17A, IL-17F and IL-23 as well as IL-23R were analysed by real-time RT-PCR. In both populations, H. pylori-infected individuals had significant higher inflammatory scores for activity and chronicity than H. pylori-negative subjects (P values between 0.006 and <0.0001). IL-8 mRNA was induced up to 6-fold in H. pylori-infected patients (P < 0.05), while the expression levels of IL-1β, IL-18, IL-23, IL-33 and IL-23R did not differ with respect to the H. pylori status in both groups. Most strikingly, a significant induction of both IL-17A and IL-17F was noted in H. pylori-infected individuals of both ethnic groups. Almost all IL-17F-positive samples revealed co-expression of IL-17A (40/42, 95.2%). Analysing IL-17A and IL-17F transcript levels of these 40 'double-positive' samples, a highly significant positive correlation between both genes was identified (P < 0.001). Taken together, H. pylori infection leads to a strong upregulation of both IL-17A and IL-17F in the gastric mucosa suggesting a regulatory link between both genes.

Activation of type I IFN signaling by NOD1 mediates mucosal host defense against Helicobacter pylori infection

Infection of gastric epithelial cells with Helicobacter pylori (H. pylori) induces a complex array of host protective immune responses. The best known are the adaptive T helper type 1 and type 17 responses that are induced in the gastric lamina propria by antigen-presenting cells via presentation of H. pylori antigens to CD4(+) T cells. Recently, it has become apparent that innate immune responses are also induced by H.pylori infection, both in epithelial cells and in underlying antigen-presenting cells. One important component of these innate responses involves the activity of NOD1, an intra-cellular sensor of peptides derived from the peptidoglycan component of the bacterial cell wall. In this review, we discuss our recent work showing that the signaling pathway utilized by NOD1 results in the generation of type I interferon and that this cytokine mediates both chemokine and cytokine responses that regulate the severity of gastric H. pylori infection.

Lack of commensal flora in Helicobacter pylori-infected INS-GAS mice reduces gastritis and delays intraepithelial neoplasia

BACKGROUND & AIMS

Transgenic FVB/N insulin-gastrin (INS-GAS) mice have high circulating gastrin levels, and develop spontaneous atrophic gastritis and gastrointestinal intraepithelial neoplasia (GIN) with 80% prevalence 6 months after Helicobacter pylori infection. GIN is associated with gastric atrophy and achlorhydria, predisposing mice to nonhelicobacter microbiota overgrowth. We determined if germfree INS-GAS mice spontaneously develop GIN and if H pylori accelerates GIN in gnotobiotic INS-GAS mice.

METHODS

We compared gastric lesions, levels of messenger RNA, serum inflammatory mediators, antibodies, and gastrin among germfree and H pylori-monoinfected INS-GAS mice. Microbiota composition of specific pathogen-free (SPF) INS-GAS mice was quantified by pyrosequencing.

RESULTS

Germfree INS-GAS mice had mild hypergastrinemia but did not develop significant gastric lesions until 9 months old and did not develop GIN through 13 months. H pylori monoassociation caused progressive gastritis, epithelial defects, oxyntic atrophy, marked foveolar hyperplasia, dysplasia, and robust serum and tissue proinflammatory immune responses (particularly males) between 5 and 11 months postinfection (P<0.05, compared with germfree controls). Only 2 of 26 female, whereas 8 of 18 male, H pylori-infected INS-GAS mice developed low to high-grade GIN by 11 months postinfection. Stomachs of H pylori-infected SPF male mice had significant reductions in Bacteroidetes and significant increases in Firmicutes.

CONCLUSIONS

Gastric lesions take 13 months longer to develop in germfree INS-GAS mice than male SPF INS-GAS mice. H pylori monoassociation accelerated gastritis and GIN but caused less severe gastric lesions and delayed onset of GIN compared with H pylori-infected INS-GAS mice with complex gastric microbiota. Changes in gastric microbiota composition might promote GIN in achlorhydric stomachs of SPF mice.

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.

Role of virulence factors and host cell signaling in the recognition of Helicobacter pylori and the generation of immune responses

Helicobacter pylori colonizes a large proportion of the world's population, with infection invariably leading to chronic, lifelong gastritis. While the infection often persists undiagnosed and without causing severe pathology, there are a number of host, bacterial and environmental factors that can influence whether infection provokes a mild inflammatory response or results in significant morbidity. Intriguingly, the most virulent H. pylori strains appear to deliberately induce the epithelial signaling cascades responsible for activating the innate immune system. While the reason for this remains unclear, the resulting adaptive immune responses are largely ineffective in clearing the bacterium once infection has become established and, as a result, inflammation likely causes more damage to the host itself.

Mucosal dendritic cell diversity in the gastrointestinal tract

The discovery of dendritic cells (DCs) in skin by Paul Langerhans in 1868 identified a cell type which has since been recognized as a key link between innate and adaptive immunity. DCs originate from bone marrow and disseminate through blood to all tissues in the body, and distinct DC subpopulations have been identified in many different tissues. DC diversity is apparent throughout all mucosal surfaces of the body, but the focus of this review article is DC diversity throughout the gastro-intestinal tract (GIT). DC subpopulations have been well characterized in the oral cavity and small intestine, but DC characterization in other regions, such as the esophagus and stomach, is limited. Substantial research has focused on DC function during disease, but understanding the regulation of inflammation and the induction of acquired immune responses requires combined phenotypic and functional characterization of individual DC subpopulations. Furthermore, little is known regarding mucosal DC subpopulations in the GIT of the neonate and how these DC populations change following colonization by commensal microflora. The current review will highlight mucosal DC diversity and discuss factors that may influence mucosal DC differentiation.

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.

Pathogenesis of Helicobacter pylori infection

Helicobacter pylori infections are thought to eventually lead to symptoms as a result of the long-lasting interactions between the bacterium and its host. Mechanisms that allow this bacterium to cause a life-long infection involve modulation of both the immune response and host cellular processes. Last year many novel findings that improve our knowledge on how H. pylori virulence factors interact with the host were reported, but because of space limitations we can only discuss a limited number of these studies. Among those are studies on the genetic variation of genes encoding outer membrane proteins and the mimicry of host antigens, factors that alter host-cell metabolism and factors that modulate the host's immune response.

Helicobacter pylori-infected macrophages induce Th17 cell differentiation

Th17 cells represent a novel subset of CD4(+) T cells, which is associated with chronic inflammation. The present study evaluated Th17 cell responses to Helicobacter pylori infection in mouse model and CD4(+) T cell differentiation in response to H. pylori-infected macrophages. Th17 cells were observed in the H. pylori-infected gastric tissue. Co-culture of CD4(+) T cells with H. pylori-infected macrophages elevated IL-17 and IFN-γ secretion, up-regulated retinoid-related orphan receptor gamma t (RORγt) and T box expressed in T cells (T-bet) expression and increased the numbers of Th17 and Th1 cells. The expression of CD40, CD80, and CD86 and the secretion of IL-6, TGF-β1, IL-23, and CCL20 were significantly increased in H. pylori-stimulated macrophages. NF-κB pathway participated in the production of IL-6, IL-23, and CCL20 from macrophages in response to H. pylori, and inhibition of NF-κB pathway of macrophages resulted in less Th17 cell differentiation. Taken together, these results suggest that H. pylori induces Th17 cell differentiation via infected macrophages.

Helicobacter pylori directs tolerogenic programming of dendritic cells

Our laboratory has shown that Helicobacter pylori infection in mice triggers an increase in the number of subepithelial lamina propria CD11c(+) dendritic cells with luminal projections. The physical characteristic of these cells is consistent with their ability to traverse epithelial tight junctions as reported by Maria Recigno.3 Gastric CD103(+) dendritic cells, which are known to induce mucosal regulatory T cells, were also increased in number, raising the question whether H. pylori infection induces a regulatory T cell-skewed response by way of a bacteria-dendritic cell interaction. In fact, bone marrow-derived dendritic cells underwent tolerogenic programming, skewing the balance between effector and regulatory T cell responses towards regulatory T cell differentiation in a transforming growth factor-β- and interleukin-10-dependent manner. Depletion of regulatory T cell numbers augmented H. pylori-specific effector helper T cell responses, which correlated with a lower degree of H. pylori colonization. These results suggest H. pylori is capable of inducing a regulatory T cell-skewed response that limits the host's ability to eradicate the bacteria, allowing the H. pylori infection to persist. To better understand the mechanism of H. pylori tolerogenic programming we compared the differential expressions of 34 genes critical for dendritic cell function in bone marrow-derived dendritic cells pulsed with live H. pylori or other Gram-negative bacteria (e.g., Escherichia coli, Acinetobacter lwoffii). Our data imply that H. pylori targets the Toll-like receptor 2 pathway to induce a regulatory T cell-skewed response. In addition, we show that H. pylori-pulsed dendritic cells are capable of inducing the conversion of naïve T cells to regulatory T cells. These observations are evidence of a unique tolerogenic program in dendritic cells that involves active editing of the immune response by H. pylori, favoring its persistence in the gastric mucosa.