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

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.

Prophylactic and therapeutic efficacy of the epitope vaccine CTB-UA against Helicobacter pylori infection in a BALB/c mice model

Epitope vaccine based on the enzyme urease of Helicobacter pylori is a promising option for prophylactic and therapeutic vaccination against H. pylori infection. In our previous study, the epitope vaccine CTB-UA, which was composed of the mucosal adjuvant cholera toxin B subunit (CTB) and an epitope (UreA₁₈₃₋₂₀₃) from the H. pylori urease A subunit (UreA) was constructed. This particular vaccine was shown to have good immunogenicity and immunoreactivity and could induce specific neutralizing antibodies, which exhibited effectively inhibitory effects on the enzymatic activity of H. pylori urease. In this study, the prophylactic and therapeutic efficacy of the epitope vaccine CTB-UA was evaluated in a BALB/c mice model. The experimental results indicated that oral prophylactic or therapeutic immunization with CTB-UA significantly decreased H. pylori colonization compared with oral immunization with PBS. The results also revealed that the protection was correlated with antigen-specific IgG, IgA, and mucosal secretory IgA antibody responses. CTB-UA may be a promising vaccine candidate for the control of H. pylori infection.

Multiple peptidoglycan modification networks modulate Helicobacter pylori's cell shape, motility, and colonization potential

Helical cell shape of the gastric pathogen Helicobacter pylori has been suggested to promote virulence through viscosity-dependent enhancement of swimming velocity. However, H. pylori csd1 mutants, which are curved but lack helical twist, show normal velocity in viscous polymer solutions and the reason for their deficiency in stomach colonization has remained unclear. Characterization of new rod shaped mutants identified Csd4, a DL-carboxypeptidase of peptidoglycan (PG) tripeptide monomers and Csd5, a putative scaffolding protein. Morphological and biochemical studies indicated Csd4 tripeptide cleavage and Csd1 crosslinking relaxation modify the PG sacculus through independent networks that coordinately generate helical shape. csd4 mutants show attenuation of stomach colonization, but no change in proinflammatory cytokine induction, despite four-fold higher levels of Nod1-agonist tripeptides in the PG sacculus. Motility analysis of similarly shaped mutants bearing distinct alterations in PG modifications revealed deficits associated with shape, but only in gel-like media and not viscous solutions. As gastric mucus displays viscoelastic gel-like properties, our results suggest enhanced penetration of the mucus barrier underlies the fitness advantage conferred by H. pylori's characteristic shape.

The hypothesis on function of glycosphingolipids and ABO blood groups revisited

Twenty-five years ago the author proposed new ideas of glycoprotein (GPs) and glycosphingolipid (GSLs) functions at the cell membrane. The GPs, apart from their glycan carrying capacity, were assumed to have specific, protein associated, functions. In contrast, GSLs such as those of globo and neolacto/lacto series, were considered to be energetically cheap membrane packing substances, filling in membrane spaces not covered with functional GPs. The terminal carbohydrate structures of the neolacto/lacto GSLs, i.e., sialic acid residues and ABH glycotopes, were postulated to have either regulatory or protective functions, respectively. A special active role was ascribed to terminal β-galactosyl residues of GSLs and GPs. Gangliosides were considered to be functional GSLs. In the present review the author discusses these old ideas in context of the contemporary knowledge and comes to the conclusion that they have not aged.

Caspase-1 has both proinflammatory and regulatory properties in Helicobacter infections, which are differentially mediated by its substrates IL-1β and IL-18

The proinflammatory cysteine protease caspase-1 is autocatalytically activated upon cytosolic sensing of a variety of pathogen-associated molecular patterns by Nod-like receptors. Active caspase-1 processes pro-IL-1β and pro-IL-18 to generate the bioactive cytokines and to initiate pathogen-specific immune responses. Little information is available on caspase-1 and inflammasome activation during infection with the gastric bacterial pathogen Helicobacter pylori. In this study, we addressed a possible role for caspase-1 and its cytokine substrates in the spontaneous and vaccine-induced control of Helicobacter infection, as well as the development of gastritis and gastric cancer precursor lesions, using a variety of experimental infection, vaccine-induced protection, and gastric disease models. We show that caspase-1 is activated and IL-1β and IL-18 are processed in vitro and in vivo as a consequence of Helicobacter infection. Caspase-1 activation and IL-1 signaling are absolutely required for the efficient control of Helicobacter infection in vaccinated mice. IL-1R(-/-) mice fail to develop protective immunity but are protected against Helicobacter-associated gastritis and gastric preneoplasia as a result of their inability to generate Helicobacter-specific Th1 and Th17 responses. In contrast, IL-18 is dispensable for vaccine-induced protective immunity but essential for preventing excessive T cell-driven immunopathology. IL-18(-/-) animals develop strongly accelerated pathology that is accompanied by unrestricted Th17 responses. In conclusion, we show in this study that the processing and release of a regulatory caspase-1 substrate, IL-18, counteracts the proinflammatory activities of another caspase-1 substrate, IL-1β, thereby balancing control of the infection with the prevention of excessive gastric immunopathology.

DC-derived IL-18 drives Treg differentiation, murine Helicobacter pylori-specific immune tolerance, and asthma protection

Persistent colonization with the gastric bacterial pathogen Helicobacter pylori causes gastritis and predisposes infected individuals to gastric cancer. Conversely, it is also linked to protection from allergic, chronic inflammatory, and autoimmune diseases. We demonstrate here that H. pylori inhibits LPS-induced maturation of DCs and reprograms DCs toward a tolerance-promoting phenotype. Our results showed that DCs exposed to H. pylori in vitro or in vivo failed to induce T cell effector functions. Instead, they efficiently induced expression of the forkhead transcription factor FoxP3, the master regulator of Tregs, in naive T cells. Depletion of DCs in mice infected with H. pylori during the neonatal period was sufficient to break H. pylori-specific tolerance. DC depletion resulted in improved control of the infection but also aggravated T cell-driven immunopathology. Consistent with the mouse data, DCs infiltrating the gastric mucosa of human H. pylori carriers exhibited a semimature DC-SIGN(+)HLA-DR(hi)CD80(lo)CD86(lo) phenotype. Mechanistically, the tolerogenic activity of H. pylori-experienced DCs was shown to require IL-18 in vitro and in vivo; DC-derived IL-18 acted directly on T cells to drive their conversion to Tregs. CD4(+)CD25(+) Tregs from infected wild-type mice but not Il18(-/-) or Il18r1(-/-) mice prevented airway inflammation and hyperresponsiveness in an experimental model of asthma. Taken together, our results indicate that tolerogenic reprogramming of DCs ensures the persistence of H. pylori and protects against allergic asthma in a process that requires IL-18.

H. pylori exploits and manipulates innate and adaptive immune cell signaling pathways to establish persistent infection

Persistent infection with the gastric bacterial pathogen Helicobacter pylori causes gastritis and predisposes carriers to a high gastric cancer risk, but has also been linked to protection from allergic, chronic inflammatory and autoimmune diseases. In the course of tens of thousands of years of co-existence with its human host, H. pylori has evolved elaborate adaptations that allow it to persist in the hostile environment of the stomach in the face of a vigorous innate and adaptive immune response. For this review, we have identified several key immune cell types and signaling pathways that appear to be preferentially targeted by the bacteria to establish and maintain persistent infection. We explore the mechanisms that allow the bacteria to avoid detection by innate immune cells via their pattern recognition receptors, to escape T-cell mediated adaptive immunity, and to reprogram the immune system towards tolerance rather than immunity. The implications of the immunomodulatory properties of the bacteria for the prevention of allergic and auto-immune diseases in chronically infected individuals are also discussed.

Effects of myeloid differentiation primary response gene 88 (MyD88) activation on Helicobacter infection in vivo and induction of a Th17 response

BACKGROUND

Helicobacter pylori is a spiral-shaped Gram-negative microaerophilic bacterium associated with a number of gastrointestinal disorders, including gastritis, peptic ulcers, and gastric cancer. Several studies have implicated a Th17 response as a key to protective immunity against Helicobacter.

MATERIALS AND METHODS

Wild type (WT) and MyD88-deficient (MyD88(-/-)) mice in the C57BL/6 background were infected with H. felis for 6 and 25 weeks and colonization density and host response evaluated. Real-time PCR was used to determine the expression of cytokines and antimicrobial peptides in the gastric tissue of mice.

RESULTS

mRNA expression levels of the Th17 cytokines interleukin-17A (IL-17A) and IL-22 were markedly up-regulated in WT compared with MyD88(-/-) mice both at 6 and at 25 weeks in response to infection with H. felis, indicating that induction of Th17 responses depends on MyD88 signaling. Furthermore, reduction in the expression of Th17-dependent intestinal antimicrobial peptide lipocalin-2 was linked with increased bacterial burden in the absence of MyD88 signaling.

CONCLUSION

We provide evidence showing that MyD88-dependent signaling is required for the host to induce a Th17 response for the control of Helicobacter infection.

Oral immunization with recombinant Mycobacterium smegmatis expressing the outer membrane protein 26-kilodalton antigen confers prophylactic protection against Helicobacter pylori infection

Helicobacter pylori infection is prevalent worldwide and results in chronic gastritis, which may lead to gastric mucosa-associated lymphoid tissue lymphoma and gastric cancer. We have previously reported that oral immunization with recombinant Mycobacterium smegmatis expressing the H. pylori outer membrane protein 26-kilodalton (Omp26) antigen affords therapeutic protection against H. pylori infection in mice. In the present study, we investigated the prophylactic effects of this vaccine candidate on H. pylori challenge in mice. We found that oral immunization with recombinant Mycobacterium Omp26 significantly reduced H. pylori colonization in the stomach compared to inoculation with wild-type M. smegmatis in control mice. Six of the recombinant Mycobacterium-immunized mice (60%) were completely protected from H. pylori infection. The severity of H. pylori-associated chronic gastritis assessed histologically was significantly milder in mice vaccinated with recombinant Mycobacterium than in control animals. Mice immunized with recombinant Mycobacterium showed enhanced antigen-specific lymphocyte proliferation and antibody responses. Moreover, immunization with recombinant Mycobacterium resulted in an increased expression of interleukin-2 and gamma interferon in the stomach and spleen, as determined by reverse transcription-PCR analysis. Our results collectively suggest that vaccination with recombinant Mycobacterium Omp26 confers prophylactic protection against H. pylori infection. The inhibition of H. pylori colonization is associated with the induction of antigen-specific humoral and cell-mediated immune responses.

Carcinogenic bacterial pathogen Helicobacter pylori triggers DNA double-strand breaks and a DNA damage response in its host cells

The bacterial pathogen Helicobacter pylori chronically infects the human gastric mucosa and is the leading risk factor for the development of gastric cancer. The molecular mechanisms of H. pylori-associated gastric carcinogenesis remain ill defined. In this study, we examined the possibility that H. pylori directly compromises the genomic integrity of its host cells. We provide evidence that the infection introduces DNA double-strand breaks (DSBs) in primary and transformed murine and human epithelial and mesenchymal cells. The induction of DSBs depends on the direct contact of live bacteria with mammalian cells. The infection-associated DNA damage is evident upon separation of nuclear DNA by pulse field gel electrophoresis and by high-magnification microscopy of metaphase chromosomes. Bacterial adhesion (e.g., via blood group antigen-binding adhesin) is required to induce DSBs; in contrast, the H. pylori virulence factors vacuolating cytotoxin A, γ-glutamyl transpeptidase, and the cytotoxin-associated gene (Cag) pathogenicity island are dispensable for DSB induction. The DNA discontinuities trigger a damage-signaling and repair response involving the sequential ataxia telangiectasia mutated (ATM)-dependent recruitment of repair factors--p53-binding protein (53BP1) and mediator of DNA damage checkpoint protein 1 (MDC1)--and histone H2A variant X (H2AX) phosphorylation. Although most breaks are repaired efficiently upon termination of the infection, we observe that prolonged active infection leads to saturation of cellular repair capabilities. In summary, we conclude that DNA damage followed by potentially imprecise repair is consistent with the carcinogenic properties of H. pylori and with its mutagenic properties in vitro and in vivo and may contribute to the genetic instability and frequent chromosomal aberrations that are a hallmark of gastric cancer.

Inflammation, immunity, and vaccine development for Helicobacter pylori

The immune response to Helicobacter pylori entails both innate effectors and a complex mix of Th1, Th17, and Treg adaptive immune responses. The clinical outcome of infection may well depend to a large degree on the relative balance of these responses. Vaccination with a wide range of antigens, adjuvants, and delivery routes can produce statistically significant reductions in H. pylori colonization levels in mice, though rarely sterilizing immunity. Whether similar reductions in bacterial load can be achieved in humans, and whether they would be clinically significant, is still unclear. However, progress in understanding the role of Th1, Th17, and most recently Treg cells in protection against H. pylori infection provides reason for optimism.

Helicobacter felis--associated gastric disease in microbiota-restricted mice

Human Helicobacter pylori infection leads to multiple pathological consequences, including gastritis and adenocarcinoma. Although this association has led to the classification of H. pylori as a type 1 carcinogen, it is not clear if additional nonhelicobacter gastric microbiota play a role in these diseases. In this study, we utilized either specific pathogen-free C57BL/6 mice (B6.SPF) or mice colonized with altered Schaedler flora (B6.ASF) to evaluate the role of nonhelicobacter gastric microbiota in disease development after Helicobacter felis infection. Despite similar histological changes, H. felis persisted in B6.ASF stomachs, while H. felis could no longer be detected in the majority of B6.SPF mice. The B6.SPF mice also acquired multiple Lactobacillus spp. in their stomachs after H. felis infection. Our data indicate that potential mechanisms responsible for the ineffective H. felis clearance in the B6.ASF model include the absence of new gastric microbiota to compete for the gastric niche, the lack of expression of new gastric mucins, and a reduced ratio of H. felis-specific IgG2c:IgG1 serum antibodies. These data suggest that although H. felis is sufficient to initiate gastric inflammation and atrophy, bacterial eradication and the systemic immune response to infection are significantly influenced by pre-existing and acquired gastric microbiota.

Coinfection with Enterohepatic Helicobacter species can ameliorate or promote Helicobacter pylori-induced gastric pathology in C57BL/6 mice

To investigate how different enterohepatic Helicobacter species (EHS) influence Helicobacter pylori gastric pathology, C57BL/6 mice were infected with Helicobacter hepaticus or Helicobacter muridarum, followed by H. pylori infection 2 weeks later. Compared to H. pylori-infected mice, mice infected with H. muridarum and H. pylori (HmHp mice) developed significantly lower histopathologic activity index (HAI) scores (P < 0.0001) at 6 and 11 months postinoculation (MPI). However, mice infected with H. hepaticus and H. pylori (HhHp mice) developed more severe gastric pathology at 6 MPI (P = 0.01), with a HAI at 11 MPI (P = 0.8) similar to that of H. pylori-infected mice. H. muridarum-mediated attenuation of gastritis in coinfected mice was associated with significant downregulation of proinflammatory Th1 (interlukin-1beta [Il-1β], gamma interferon [Ifn-γ], and tumor necrosis factor-alpha [Tnf-α]) cytokines at both time points and Th17 (Il-17A) cytokine mRNA levels at 6 MPI in murine stomachs compared to those of H. pylori-infected mice (P < 0.01). Coinfection with H. hepaticus also suppressed H. pylori-induced elevation of gastric Th1 cytokines Ifn-γ and Tnf-α (P < 0.0001) but increased Th17 cytokine mRNA levels (P = 0.028) at 6 MPI. Furthermore, mRNA levels of Il-17A were positively correlated with the severity of helicobacter-induced gastric pathology (HhHp>H. pylori>HmHp) (at 6 MPI, r² = 0.92, P < 0.0001; at 11 MPI, r² = 0.82, P < 0.002). Despite disparate effects on gastritis, colonization levels of gastric H. pylori were increased in HhHp mice (at 6 MPI) and HmHp mice (at both time points) compared to those in mono-H. pylori-infected mice. These data suggest that despite consistent downregulation of Th1 responses, EHS coinfection either attenuated or promoted the severity of H. pylori-induced gastric pathology in C57BL/6 mice. This modulation was related to the variable effects of EHS on gastric interleukin 17 (IL-17) responses to H. pylori infection.

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.

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 C-terminally encoded, MHC class II-restricted T cell antigenicity of the Helicobacter pylori virulence factor CagA promotes gastric preneoplasia

Chronic infection with the human bacterial pathogen Helicobacter pylori causes gastritis and predisposes carriers to an increased gastric cancer risk. Consequently, H. pylori-specific vaccination is widely viewed as a promising strategy of gastric cancer prevention. H. pylori strains harboring the Cag pathogenicity island (PAI) are associated with particularly unfavorable disease outcomes in humans and experimental rodent models. We show in this study using a C57BL/6 mouse model of Cag-PAI(+) H. pylori infection that the only known protein substrate of the Cag-PAI-encoded type IV secretion system, the cytotoxin-associated gene A (CagA) protein, harbors MHC class II-restricted T cell epitopes. Several distinct nonoverlapping epitopes in CagA's central and C-terminal regions were predicted in silico and could be confirmed experimentally. CagA(+) infection elicits CD4(+) T cell responses in mice, which are strongly enhanced by prior mucosal or parenteral vaccination with recombinant CagA. The adoptive transfer of CagA-specific T cells to T cell-deficient, H. pylori-infected recipients is sufficient to induce the full range of preneoplastic immunopathology. Similarly, immunization with a cholera toxin-adjuvanted, CagA(+) whole-cell sonicate vaccine sensitizes mice to, rather than protects them from, H. pylori-associated gastric cancer precursor lesions. In contrast, H. pylori-specific tolerization by neonatal administration of H. pylori sonicate in conjunction with a CD40L-neutralizing Ab prevents H. pylori-specific, pathogenic T cell responses and gastric immunopathology. We conclude that active tolerization may be superior to vaccination strategies in gastric cancer prevention.

Comparative whole genome sequence analysis of the carcinogenic bacterial model pathogen Helicobacter felis

The gram-negative bacterium Helicobacter felis naturally colonizes the gastric mucosa of dogs and cats. Due to its ability to persistently infect laboratory mice, H. felis has been used extensively to experimentally model gastric disorders induced in humans by H. pylori. We determined the 1.67 Mb genome sequence of H. felis using combined Solexa and 454 pyrosequencing, annotated the genome, and compared it with multiple previously published Helicobacter genomes. About 1,063 (63.6%) of the 1,671 genes identified in the H. felis genome have orthologues in H. pylori, its closest relative among the fully sequenced Helicobacter species. Many H. pylori virulence factors are shared by H. felis: these include the gamma-glutamyl transpeptidase GGT, the immunomodulator NapA, and the secreted enzymes collagenase and HtrA. Helicobacter felis lacks a Cag pathogenicity island and the vacuolating cytotoxin VacA but possesses a complete comB system conferring natural competence. Remarkable features of the H. felis genome include its paucity of transcriptional regulators and an extraordinary abundance of chemotaxis sensors and restriction/modification systems. Helicobacter felis possesses an episomally replicating 6.7-kb plasmid and harbors three chromosomal regions with deviating GC content. These putative horizontally acquired regions show homology and synteny with the recently isolated H. pylori plasmid pHPPC4 and homology to Campylobacter bacteriophage genes (transposases, structural, and lytic genes), respectively. In summary, the H. felis genome harbors a variety of putative mobile elements that are unique among Helicobacter species and may contribute to this pathogen’s carcinogenic properties.

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.

Tolerance rather than immunity protects from Helicobacter pylori-induced gastric preneoplasia

BACKGROUND & AIMS

Chronic infection with the bacterial pathogen Helicobacter pylori causes gastric disorders, ranging from chronic gastritis to gastric adenocarcinoma. Only a subset of infected persons will develop overt disease; most remains asymptomatic despite lifelong colonization. This study aims to elucidate the differential susceptibility to H pylori that is found both across and within populations.

METHODS

We have established a C57BL/6 mouse model of H pylori infection with a strain that is capable of delivering the virulence factor cytotoxin-associated gene A (CagA) into host cells through the activity of a Cag-pathogenicity island-encoded type IV secretion system.

RESULTS

Mice infected at 5-6 weeks of age with CagA(+)H pylori rapidly develop gastritis, gastric atrophy, epithelial hyperplasia, and metaplasia in a type IV secretion system-dependent manner. In contrast, mice infected during the neonatal period with the same strain are protected from preneoplastic lesions. Their protection results from the development of H pylori-specific peripheral immunologic tolerance, which requires transforming growth factor-β signaling and is mediated by long-lived, inducible regulatory T cells, and which controls the local CD4(+) T-cell responses that trigger premalignant transformation. Tolerance to H pylori develops in the neonatal period because of a biased ratio of T-regulatory to T-effector cells and is favored by prolonged low-dose exposure to antigen.

CONCLUSIONS

Using a novel CagA(+)H pylori infection model, we report here that the development of tolerance to H pylori protects from gastric cancer precursor lesions. The age at initial infection may thus account for the differential susceptibility of infected persons to H pylori-associated disease manifestations.

TLR-2-activated B cells suppress Helicobacter-induced preneoplastic gastric immunopathology by inducing T regulatory-1 cells

B cells regulate autoimmune pathologies and chronic inflammatory conditions such as autoimmune encephalomyelitis and inflammatory bowel disease. The potential counterregulatory role of B cells in balancing pathogen-specific immune responses and the associated immunopathology is less well understood owing to the lack of appropriate persistent infection models. In this paper, we show that B cells have the ability to negatively regulate adaptive immune responses to bacterial pathogens. Using mouse models of infection with Helicobacter felis, a close relative of the human gastrointestinal pathogen H. pylori, we found that B cells activated by Helicobacter TLR-2 ligands induce IL-10-producing CD4(+)CD25(+) T regulatory-1 (Tr-1)-like cells in vitro and in vivo. Tr-1 conversion depends on TCR signaling and a direct T-/B-interaction through CD40/CD40L and CD80/CD28. B cell-induced Tr-1 cells acquire suppressive activity in vitro and suppress excessive gastric Helicobacter-associated immunopathology in vivo. Adoptive cotransfer of MyD88-proficient B cells and Tr-1 cells restores a normal gastric mucosal architecture in MyD88(-/-) and IL-10(-/-) mice in a manner that depends on T cellular, but not B cellular, IL-10 production. Our findings describe a novel mechanism of B cell-dependent Tr-1 cell generation and function in a clinically relevant disease model. In conclusion, we demonstrate that the B cell/Tr-1 cell axis is essential for balancing the control of Helicobacter infection with the prevention of excessive Th1-driven gastric immunopathology, promoting gastric mucosal homeostasis on the one hand and facilitating Helicobacter persistence on the other.

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.

Proinflammatory cytokine gene expression in the stomach correlates with vaccine-induced protection against Helicobacter pylori infection in mice: an important role for interleukin-17 during the effector phase

CD4(+) T cells have been shown to be essential for vaccine-induced protection against Helicobacter pylori infection in mice. Less is known about the relative contributions of individual cell subpopulations, such as T(h)1 and T(h)17 cells, and their associated cytokines. The aim of the present study was to find immune correlates to vaccine-induced protection and further study their role in protection against H. pylori infection. Immunized and unimmunized mice were challenged with H. pylori, and immune responses were compared. Vaccine-induced protection was assessed by measuring H. pylori colonization in the stomach. Gastric gene expression of T(h)1- and/or T(h)17-associated cytokines was analyzed by quantitative PCR, and contributions of individual cytokines to protection were evaluated by antibody-mediated in vivo neutralization. By analyzing immunized and unimmunized mice, a significant inverse correlation between the levels of interleukin-12p40 (IL-12p40), tumor necrosis factor alpha (TNF), gamma interferon (IFN-γ), and IL-17 gene expression and the number of H. pylori bacteria in the stomachs of individual animals after challenge could be demonstrated. In a kinetic study, upregulation of TNF, IFN-γ, and IL-17 coincided with vaccine-induced protection at 7 days after H. pylori challenge and was sustained for at least 21 days. In vivo neutralization of these cytokines during the effector phase of the immune response revealed a significant role for IL-17, but not for IFN-γ or TNF, in vaccine-induced protection. In conclusion, although both T(h)1- and T(h)17-associated gene expression in the stomach correlate with vaccine-induced protection against H. pylori infection, our study indicates that mainly T(h)17 effector mechanisms are of critical importance to protection.

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.

Inhibition of ADP ribosylation prevents and cures helicobacter-induced gastric preneoplasia

Gastric adenocarcinoma develops as a consequence of chronic inflammation of the stomach lining that is caused by persistent infection with the bacterium Helicobacter pylori. Gastric carcinogenesis progresses through a sequence of preneoplastic lesions that manifest histologically as atrophic gastritis, intestinal metaplasia, and dysplasia. We show here in several preclinical models of Helicobacter-induced atrophic gastritis, epithelial hyperplasia, and metaplasia that the inhibition of ADP ribosylation by the small-molecule inhibitor PJ34 not only prevents the formation of gastric cancer precursor lesions, but also efficiently reverses preexisting lesions. PJ34 exerts its chemopreventive and therapeutic effects by impairing Helicobacter-specific T-cell priming and T(H)1 polarization in the gut-draining mesenteric lymph nodes. The subsequent infiltration of pathogenic T cells into the gastric mucosa and the ensuing gastric T cell-driven immunopathology are prevented efficiently by PJ34. Our data indicate that PJ34 directly suppresses T-cell effector functions by blocking the IFN-gamma production of mesenteric lymph node T cells ex vivo. Upon exposure to PJ34, purified T cells failed to synthesize ADP-ribose polymers and to activate the transcription of genes encoding IFN-gamma, interleukin 2, and the interleukin 2 receptor alpha chain in response to stimuli such as CD3/CD28 cross-linking or phorbol 12-myristate 13-acetate/ionomycin. The immunosuppressive and chemoprotective effects of PJ34 therefore result from impaired T-cell activation and T(H)1 polarization, and lead to the protection from preneoplastic gastric immunopathology. In conclusion, ADP-ribosylating enzymes constitute novel targets for the treatment of Helicobacter-associated gastric lesions predisposing infected individuals to gastric cancer and may also hold promise for the treatment of other T cell-driven chronic inflammatory conditions and autoimmune pathologies.

B-cell receptor signaling and CD40 ligand-independent T cell help cooperate in Helicobacter-induced MALT lymphomagenesis

Gastric B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) develops in the context of chronic inflammation caused by Helicobacter pylori infection. Most pathophysiological features of the early stages of MALT lymphomagenesis can be reproduced by experimental infection of BALB/c mice with Helicobacter species. We have previously shown that MALT lymphomas are infiltrated by T-helper cell type 2-polarized T cells and that human and murine tumor B cells carry polyreactive surface immunoglobulins. Using the murine model of the disease, in this study we show that explanted tumor B cells proliferate upon stimulation with the same panel of self and foreign antigens that are recognized by their surface antibodies. Tumor cell proliferation is strongly enhanced by the presence of intratumoral CD4(+) T cells in a CD40/CD40L-independent manner. A large proportion of tumor-infiltrating CD4(+) T cells are CD25(+)FoxP3(+) regulatory T cells (Tregs) with highly suppressive activity, which are recruited by the tumor cells through secretion of the Treg-attracting chemokines CCL17 and CCL22. The depletion of CD25(+) cells was as efficient as CD4(+) T cell depletion in blocking tumor growth in vitro and in vivo. In conclusion, our data suggest that B-cell receptor-derived signals cooperate with T-helper cell signals in driving the progression of MALT lymphoma, providing an explanation for the unique antigen dependence of this B-cell malignancy.

Prostaglandin E2 prevents Helicobacter-induced gastric preneoplasia and facilitates persistent infection in a mouse model

BACKGROUND & AIMS

Persistent infection with the human pathogen Helicobacter pylori increases the risk of gastric cancer. In this study, we investigated the role of cyclooxygenase-2 (COX-2) and its main product, prostaglandin E(2) (PGE(2)), in the development of Helicobacter-induced gastritis and gastric cancer precursor lesions.

METHODS

We utilized mouse models of Helicobacter-induced gastric preneoplasia and vaccine-induced protection to study the effects of COX-2 inhibition and PGE(2) treatment on the induction of Helicobacter-specific immune responses and gastric premalignant immunopathology.

RESULTS

COX-2 and PGE(2) are up-regulated upon Helicobacter infection in cultured epithelial cells and in the gastric mucosa of infected mice. Inhibition of COX-2 activity with celecoxib significantly accelerated early preneoplasia; conversely, systemic administration of synthetic PGE(2) prevented development of premalignant pathology and completely reversed preexisting lesions by suppressing interferon-gamma production in the infected stomachs. The protective effect of PGE(2) was accompanied by increased Helicobacter colonization in all models. All in vivo effects were attributed to immunosuppressive effects of PGE(2) on CD4(+) T-helper 1 cells, which fail to migrate, proliferate, and secrete cytokines when exposed to PGE(2) in vitro and in vivo. T-cell inhibition was found to be due to silencing of interleukin-2 gene transcription, and could be overcome by supplementation with recombinant interleukin-2 in vitro and in vivo.

CONCLUSIONS

COX-2-dependent production of PGE(2) has an important immunomodulatory role during Helicobacter infection, preventing excessive local immune responses and the associated immunopathology by inhibiting the effector functions of pathogenic T-helper 1 cells.

What a fish can learn from a mouse: principles and strategies for modeling human cancer in mice

This review highlights the current techniques used to generate transgenic mouse models of cancer, with an emphasis on recent advances in the use of ubiquitous promoters, models that use Cre-loxP and Flip-FRT recombinase technology, inducible systems, RNAi to target genes, and transposon mutagenesis. A concluding section discusses new imaging systems that visualize tumor progression and the microenvironment in vivo. In this review, these techniques and strategies used in mouse models of cancer are highlighted, as they are pertinent and relevant to the development of zebrafish models of cancer.

Interferon-gamma secretion is induced in IL-12 stimulated human NK cells by recognition of Helicobacter pylori or TLR2 ligands

Helicobacter pylori induce a chronic inflammation in the human gastric mucosa characterized by increased production of interferon-gamma (IFN-γ). The presence of natural killer (NK) cells in the human gastric mucosa and the ability of NK cells to produce IFN-γ suggest an important role of NK cells in the immune response directed towards H. pylori infection. Since NK cells previously have been shown to respond to bacterial components with IFN-γ production, we investigated the mechanisms for the recognition of H. pylori. We found that inhibition of MyD88 homodimerization resulted in decreased production of IFN-γ and that inhibition of the p38 MAPK decreased the production as well as the secretion of IFN-γ. Further studies indicated an involvement of Toll-like receptors (TLRs), in particular TLR2. Finally, we showed that the H. pylori specific membrane bound lipoprotein HpaA induced IFN-γ production from NK cells through recognition by TLR2. In conclusion, we suggest an involvement of TLR2 in the recognition of H. pylori by human NK cells and that HpaA is a TLR2 ligand important for recognition.