The role of genome diversity and immune evasion in persistent infection with Helicobacter pylori

Impact of Mast Cell Activation on Neurodegeneration: A Potential Role for Gut-Brain Axis and Helicobacter pylori Infection

BACKGROUND

The innate immune response aims to prevent pathogens from entering the organism and/or to facilitate pathogen clearance. Innate immune cells, such as macrophages, mast cells (MCs), natural killer cells and neutrophils, bear pattern recognition receptors and are thus able to recognize common molecular patterns, such as pathogen-associated molecular patterns (PAMPs), and damage-associated molecular patterns (DAMPs), the later occurring in the context of neuroinflammation. An inflammatory component in the pathology of otherwise "primary cerebrovascular and neurodegenerative" disease has recently been recognized and targeted as a means of therapeutic intervention. Activated MCs are multifunctional effector cells generated from hematopoietic stem cells that, together with dendritic cells, represent first-line immune defense mechanisms against pathogens and/or tissue destruction.

METHODS

This review aims to summarize evidence of MC implication in the pathogenesis of neurodegenerative diseases, namely, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, and multiple sclerosis.

RESULTS

In view of recent evidence that the gut-brain axis may be implicated in the pathogenesis of neurodegenerative diseases and the characterization of the neuroinflammatory component in the pathology of these diseases, this review also focuses on MCs as potential mediators in the gut-brain axis bi-directional communication and the possible role of Helicobacter pylori, a gastric pathogen known to alter the gut-brain axis homeostasis towards local and systemic pro-inflammatory responses.

CONCLUSION

As MCs and Helicobacter pylori infection may offer targets of intervention with potential therapeutic implications for neurodegenerative disease, more clinical and translational evidence is needed to elucidate this field.

Evolved to vary: genome and epigenome variation in the human pathogen Helicobacter pylori

Helicobacter pylori is a Gram-negative, spiral shaped bacterium that selectively and chronically infects the gastric mucosa of humans. The clinical course of this infection can range from lifelong asymptomatic infection to severe disease, including peptic ulcers or gastric cancer. The high mutation rate and natural competence typical of this species are responsible for massive inter-strain genetic variation exceeding that observed in all other bacterial human pathogens. The adaptive value of such a plastic genome is thought to derive from a rapid exploration of the fitness landscape resulting in fast adaptation to the changing conditions of the gastric environment. Nevertheless, diversity is also lost through recurrent bottlenecks and H. pylori's lifestyle is thus a perpetual race to maintain an appropriate pool of standing genetic variation able to withstand selection events. Another aspect of H. pylori's diversity is a large and variable repertoire of restriction-modification systems. While not yet completely understood, methylome evolution could generate enough transcriptomic variation to provide another intricate layer of adaptive potential. This review provides an up to date synopsis of this rapidly emerging area of H. pylori research that has been enabled by the ever-increasing throughput of Omics technologies and a multitude of other technological advances.

Heterogeneity of Helicobacter pylori Strains Isolated from Patients with Gastric Disorders in Guiyang, China

Purpose

Chronic Helicobacter pylori infection causes peptic ulcers in a subpopulation of individuals and is a risk factor for the development of gastric cancer. Multiple infections and heteroresistant H. pylori contribute to poor treatment efficacy. Here, we investigated the extent of genetic diversity among H. pylori strains within a given host and its influence on the results of antibiotic (metronidazole, levofloxacin, clarithromycin, amoxicillin, and tetracycline) susceptibility testing.

Materials and Methods

Gastric mucosa biopsy samples were obtained from patients with gastric disorders, including 48 H. pylori positive patients, who were never previously treated for H. pylori infection. Five potential H. pylori colonies isolated from each sample were subcultured for enrichment. Enriched H. pylori colonies were identified through Gram staining and assays for urease, oxidase, and catalase. For each H. pylori monoclonal colony, the antibiotic susceptibility was assessed, genomic DNA was sequenced, and the cytotoxin-associated gene A (cagA) genotype was verified. Co-infection with multiple H. pylori strains was determined using random amplified polymorphic DNA (RAPD)-polymerase chain reaction (PCR).

Results

Thirteen gastric mucosa biopsy samples were positive for H. pylori. Five monoclonal strains isolated from each of these 13 patients were identified as H. pylori. RAPD-PCR indicated that intra-patient monoclonal strains of H. pylori in 10 of the 13 samples exhibited heterogeneity. Among the 13 patients, intra-patient monoclonal strains isolated from 4 patients had identical cagA genotype, whereas intra-patient monoclonal strains isolated from the other 9 patients harbored more than one cagA genotype. The antibiotic susceptibility of five intra-patient monoclonal strains from seven patients was inconsistent.

Conclusion

The existence of heterogeneous H. pylori strains with resistance to different drugs and virulence were common within the gastric mucosa of an individual patient.

Dendritic cell-derived TGF-β mediates the induction of mucosal regulatory T-cell response to Helicobacter infection essential for maintenance of immune tolerance in mice

BACKGROUND

Helicobacter pylori infection leads to regulatory T-cell (Treg) induction in infected mice, which contributes to H. pylori immune escape. However, the mechanisms responsible for H. pylori induction of Treg and immune tolerance remain unclear. We hypothesized DC-produced TGF-β may be responsible for Treg induction and immune tolerance.

MATERIALS AND METHODS

To test this hypothesis, we generated TGF-β^∆DC mice (CD11c⁺ DC-specific TGF-β deletion) and assessed the impact of DC-specific TGF-β deletion on DC function during Helicobacter infection in vitro and in vivo. To examine the T cell-independent DC function, we crossed TGF-β^∆DC mice onto Rag1KO background to generate TGF-β^∆DC xRag1KO mice.

RESULTS

When stimulated with H. pylori, TGF-β^∆DC BMDC/splenocyte cocultures showed increased levels of proinflammatory cytokines and decreased levels of anti-inflammatory cytokines compared to control, indicating a proinflammatory DC phenotype. Following 6 months of H. felis infection, TGF-β^∆DC mice developed more severe gastritis and a trend toward more metaplasia compared to TGF-β^fl/fl with increased levels of inflammatory Th1 cytokine mRNA and lower gastric H. felis colonization compared to infected TGF-β^fl/fl mice. In a T cell-deficient background using TGF-β^∆DC xRag1KO mice, H. felis colonization was significantly lower when DC-derived TGF-β was absent, revealing a direct, innate function of DC in controlling H. felis infection independent of Treg induction.

CONCLUSIONS

Our findings indicate that DC-derived TGF-β mediates Helicobacter-induced Treg response and attenuates the inflammatory Th1 response. We also demonstrated a previously unrecognized innate role of DC controlling Helicobacter colonization via a Treg-independent mechanism. DC TGF-β signaling may represent an important target in the management of H. pylori.

An In Vitro Model to Investigate the Role of Helicobacter pylori in Type 2 Diabetes, Obesity, Alzheimer's Disease and Cardiometabolic Disease

Helicobacter pylori (Hp) is a Gram-negative bacterium colonizing the human stomach. Nuclear Magnetic Resonance (NMR) analysis of intracellular human gastric carcinoma cells (MKN-28) incubated with the Hp cell filtrate (Hpcf) displays high levels of amino acids, including the branched chain amino acids (BCAA) isoleucine, leucine, and valine. Polymerase chain reaction (PCR) Array Technology shows upregulation of mammalian Target Of Rapamycin Complex 1 (mTORC1), inflammation, and mitochondrial dysfunction. The review of literature indicates that these traits are common to type 2 diabetes, obesity, Alzheimer’s diseases, and cardiometabolic disease. Here, we demonstrate how Hp may modulate these traits. Hp induces high levels of amino acids, which, in turn, activate mTORC1, which is the complex regulating the metabolism of the host. A high level of BCAA and upregulation of mTORC1 are, thus, directly regulated by Hp. Furthermore, Hp modulates inflammation, which is functional to the persistence of chronic infection and the asymptomatic state of the host. Finally, in order to induce autophagy and sustain bacterial colonization of gastric mucosa, the Hp toxin VacA localizes within mitochondria, causing fragmentation of these organelles, depletion of ATP, and oxidative stress. In conclusion, our in vitro disease model replicates the main traits common to the above four diseases and shows how Hp may potentially manipulate them.

Upregulation of Soluble HLA-G5 and HLA-G6 Isoforms in the Milder Histopathological Stages of Helicobacter pylori Infection: A Role for Subverting Immune Responses?

The subversion mechanisms employed by Helicobacter pylori (H. pylori) to escape from immune surveillance and to establish persistent infection are poorly understood. Growing evidence indicates that expression of HLA-G, a non-classical major histocompatibility complex molecule, negatively regulates immune responses in pathological conditions, including infectious diseases. In this context, we aimed to evaluate HLA-G expression in the gastric microenvironment of individuals harbouring H. pylori and to correlate it with histological variables. Fifty-four gastric specimens from patients harbouring H. pylori infection were evaluated by immunohistochemistry using anti-HLA-G monoclonal antibody. As a result, HLA-G expression was detected in 43 of 54 specimens harbouring H. pylori. The presence of HLA-G was significantly associated with milder colonization by H. pylori (P < 0.02), milder inflammatory activity (P < 0.02) and bacterium histological location in the gastric antrum. This study is the first to explore HLA-G expression in the context of bacterial infection. Whether the biological role of HLA-G during H. pylori infection is beneficial or hazardous for patients remains to be defined.

Fragmentation of CagA Reduces Hummingbird Phenotype Induction by Helicobactor pylori

Infection with Helicobacter pylori (H. pylori) has been linked to various gastro-intestinal diseases; nevertheless it remains to be clarified why only a minority of infected individuals develop illness. Studies from the West have indicated that the cagA gene and the associated EPIYA genotype of H. pylori is closely linked to the development of severe gastritis and gastric carcinoma; however, as yet no consistent correlation has been found among the bacteria from East Asia. In addition to genotype variation, the CagA protein undergoes fragmentation; however, the functional significance of fragmentation with respect to H. pylori infection remains unknown. In this study, we isolated 594 H. pylori colonies from 99 patients and examined the fragmentation patterns of CagA protein using immunoblotting. By analyzing the ability of the isolates to induce the host cell morphological transition to the highly invasive hummingbird phenotype, we demonstrated that H. pylori colonies with substantial CagA fragmentation are less potent in terms of causing this morphological transition. Our results uncovered a functional role for CagA fragmentation with respect to H. pylori-induced hummingbird phenotype formation and these findings suggest the possibility that the post-translational processing of CagA may be involved in H. pylori infection pathogenesis.

Genetic diversity and phylogenetic analysis of Tams1 of Theileria annulata isolates from three continents between 2000 and 2012

Theileria annulata, which is part of the Theileria sergenti/Theileria buffeli/Theileria orientalis group, preferentially infects cattle and results in high mortality and morbidity in the Mediterranean, Middle East, and Central Asia. The polypeptide Tams1 is an immunodominant major merozoite piroplasm surface antigen of T. annulata that could be used as a marker for epidemiological studies and phylogenetic analysis. In the present study, a total of 155 Tams1 sequences were investigated for genetic diversity and phylogenetic relationships through phylogenetic analysis. Results showed that the Tams1 sequences were divided into two major groups and that distribution for some isolates also exhibited geographic specificity. As targeting polymorphic genes for parasite detection may result in underestimation of infection, polymerase chain reaction (PCR) assay using two different probes targeting tams-1 genes of these two groups can be more credible. In addition, the direction of the spread of the disease was discovered to be from the Mediterranean or the tropical zone to the Eurasian peninsula, Middle East, Southern Asia, and Africa, particularly for Group 2. A similar occurrence was also found between the Ms1 gene of Theileria lestoquardi and the Tams1 gene of T. annulata, which explains cross-immunogenicity to a certain extent. However, no potential glycosylation site in the Tams1 of T. annulata was found in this study, which illustrated that instead of N-glycosylation, other modifications have more significant effects on the immunogenicity of the Tams1 protein.

Helicobacter pylori and gastric cancer: Indian enigma

Helicobacter pylori (H. pylori) is a gram negative microaerophilic bacterium which resides in the mucous linings of the stomach. It has been implicated in the causation of various gastric disorders including gastric cancer. The geographical distribution and etiology of gastric cancer differ widely in different geographical regions and H. pylori, despite being labeled as a grade I carcinogen, has not been found to be associated with gastric cancer in many areas. Studies in Asian countries such as Thailand, India, Bangladesh, Pakistan, Iran, Saudi Arabian countries, Israel and Malaysia, have reported a high frequency of H. pylori infection co-existing with a low incidence of gastric cancer. In India, a difference in the prevalence of H. pylori infection and gastric cancer has been noted even in different regions of the country leading to a puzzle when attempting to find the causes of these variations. This puzzle of H. pylori distribution and gastric cancer epidemiology is known as the Indian enigma. In this review we have attempted to explain the Indian enigma using evidence from various Indian studies and from around the globe. This review covers aspects of epidemiology, the various biological strains present in different parts of the country and within individuals, the status of different H. pylori-related diseases and the molecular pathogenesis of the bacterium.

Toll-like receptors and cytokines are upregulated during Helicobacter pylori infection in children

BACKGROUND AND AIM

Helicobacter pylori infection is mainly acquired during childhood, and establishes a chronic infection that may lead to peptic ulcer or gastric cancer during adulthood. Toll-like receptors (TLRs) are expressed by distinct cell types throughout the gastrointestinal tract, and play an important role in regulation of the innate immune response. Few works have addressed TLRs expression in gastric epithelia of adults, and scarce studies have done it in children. The aim of this work was to analyze the expression of TLR2, TLR4, TLR5, TLR9, and IL-8, IL-10 and TNF-α in the gastric mucosa of children with and without H. pylori infection.

METHODS

Gastric biopsies were collected by endoscopy from 50 children with recurrent abdominal pain, 25 with H. pylori infection and 25 without infection. In the gastric biopsies the expression of TLRs and cytokines was studied by immunohistochemistry, and the degree of mucosal inflammation was determined using the Sydney system.

RESULTS

We found that H. pylori infection was associated with a significant increased expression of TLRs 2, 4, 5 and 9, although expression varied between surface epithelia and glands. Epithelial cells expressing IL-8, IL-10 and TNF-α were increased in gastric mucosa of children with H. pylori infection.

CONCLUSION

This study shows the gastric epithelia of children respond to H. pylori infection by increasing the expression of TLR2, TLR4, TLR5, TLR9 and the cytokines IL-8, IL-10 and TNF-α.

Ethnicity association of Helicobacter pylori virulence genotype and metronidazole susceptibility

AIM: To characterise the cag pathogenicity island in Helicobacter pylori (H. pylori) isolates by analysing the strains’vacA alleles and metronidazole susceptibilities in light of patient ethnicity and clinical outcome.

METHODS: Ninety-five H. pylori clinical isolates obtained from patients with dyspepsia living in Malaysia were analysed in this study. Six genes in the cagPAI region (cagE, cagM, cagT, cag13, cag10 and cag67) and vacA alleles of the H. pylori isolates were identified by polymerase chain reaction. The isolates’ metronidazole susceptibility was also determined using the E-test method, and the resistant gene was characterised by sequencing.

RESULTS: More than 90% of the tested isolates had at least one gene in the cagPAI region, and cag67 was predominantly detected in the strains isolated from the Chinese patients, compared with the Malay and Indian patients (P < 0.0001). The majority of the isolates (88%) exhibited partial deletion (rearrangement) in the cagPAI region, with nineteen different patterns observed. Strains with intact or deleted cagPAI regions were detected in 3.2% and 8.4% of isolates, respectively. The prevalence of vacA s1m1 was significantly higher in the Malay and Indian isolates, whereas the isolates from the Chinese patients were predominantly genotyped as vacA s1m2 (P = 0.018). Additionally, the isolates from the Chinese patients were more sensitive to metronidazole than the isolates from the Malay and Indian patients (P = 0.047). Although we attempted to relate the cagPAI genotypes, vacA alleles and metronidazole susceptibilities to disease outcome, no association was observed. The vacA alleles were distributed evenly among the strains with intact, partially deleted or deleted cagPAI regions. Interestingly, the strains exhibiting an intact cagPAI region were sensitive to metronidazole, whereas the strains with a deleted cagPAI were more resistant.

CONCLUSION: Successful colonisation by different H. pylori genotypes is dependent on the host’s genetic makeup and may play an important role in the clinical outcome.

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.

Multiple infection and microdiversity among Helicobacter pylori isolates in a single host in India

Helicobacter pylori is one of the most diverse bacterial species that chronically infects more than 70% of Indian population. Interestingly, data showing microdiversity of the H. pylori strains within a particular gastric niche remained scarce. To understand the extent of genetic diversity among H. pylori strains within a given host, 30 patients with gastro-duodenal problems were subjected to endoscopy and from each patient 10 single colonies were isolated. Characterization of each of these 10 single colonies by DNA fingerprinting as well as genotyping of several important genetic markers viz. cagA, vacA, iceA, vapD, cag PAI empty site, IS605, RFLP and two other genetic segments within cag PAI revealed that all of the 30 patients were infected with more than one strain and sometimes strains with 5 to 6 types of genetic variants. Analyses of certain genetic loci showed the microdiversity among the colonies from single patient, which may be due to the recombination events during long-term carriage of the pathogen. These results suggest that most of the patients have acquired H. pylori due to repeated exposure to this pathogen with different genetic make-up, which may increase the possibility of super infections. Genetic exchanges between these unrelated H. pylori strains may support certain H. pylori variant to grow better in a given host than the parental strain and thereby increasing the possibility for the severity of the infection.

Stimulation of dendritic cells with Helicobacter pylori vacuolating cytotoxin negatively regulates their maturation via the restoration of E2F1

Helicobacter pylori induces an infiltration of dendritic cells (DCs) into the infected gastric mucosa. Although DCs play an important role in the regulation of inflammation, the effects of H. pylori vacuolating cytotoxin (VacA) on DC maturation process have not yet been elucidated. The role of VacA in DC maturation following co-exposure to Escherichia coli lipopolysaccharide (LPS) was investigated. The treatment of immature DCs with LPS up-regulated the expression of surface molecules [e.g. CD40, CD80, CD86 and major histocompatibility complex (MHC) class II], as well as the production of cytokines [e.g. interleukin (IL)-1β, IL-12p70 and tumour necrosis gactor (TNF)-α] compared with those of unstimulated controls. Co-stimulation with H. pylori VacA significantly reduced the up-regulated DC maturation markers induced by LPS. In addition, VacA sustained the immature state of DCs with high endocytosis and low migratory capacity. The LPS-induced down-regulation of E2F1 expression in DCs was recovered by co-stimulation with VacA. Moreover, suppression of E2F1 by small interfering RNA resulted in a significant recovery of the inhibited DC maturation by VacA. In contrast, VacA did not affect nuclear factor (NF)-κB responses to LPS and the NF-κB signal was not associated with VacA-induced inhibition of DC maturation. These results suggest that the exposure of DCs to H. pylori VacA negatively regulates DC maturation via the restoration of E2F1. The immunomodulatory action of VacA on DCs may contribute to the ability of VacA-producing H. pylori to establish a persistent infection in the gastric mucosa.

Crystallization and preliminary crystallographic studies of Helicobacter pylori arginase

Helicobacter pylori arginase is an important factor in evasion of the host's immune system and contributes to persistent infection by this bacterium. It is unique in many aspects compared with other arginases: for example, it has optimal activity with Co(2+) as a cofactor rather than Mn(2+) and has strongest activity at acidic pH instead of alkaline pH. In this study, H. pylori arginase was purified and crystallized in complex with Mn(2+) and a diffraction data set was collected to 2.2 Å resolution. The crystals belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 94.69, b = 102.24, c = 148.61 Å.

Molecular cross-talk between Helicobacter pylori and human gastric mucosa

Helicobacter pylori (H. pylori) has co-evolved with humans to be transmitted from person to person and to colonize the stomach persistently. A well-choreographed equilibrium between the bacterial effectors and host responses permits microbial persistence and health of the host, but confers a risk for serious diseases including gastric cancer. During its long coexistence with humans, H. pylori has developed complex strategies to limit the degree and extent of gastric mucosal damage and inflammation, as well as immune effector activity. The present editorial thus aims to introduce and comment on major advances in the rapidly developing area of H. pylori/human gastric mucosa interaction (and its pathological sequelae), which is the result of millennia of co-evolution of, and thus of reciprocal knowledge between, the pathogen and its human host.

Helicobacter pylori immune escape is mediated by dendritic cell-induced Treg skewing and Th17 suppression in mice

BACKGROUND & AIMS

Helicobacter pylori infection increases gastric regulatory T cell (Treg) response, which may contribute to H pylori immune escape. We hypothesize that H pylori directs Treg skewing by way of dendritic cells (DCs) and thus inhibits interleukin-17(+) helper T cells (Th17) immunity.

METHODS

Two-photon microscopy was used to locate DCs in gastric lamina propria of mice. The induction of Th17 and Treg responses by bacteria-pulsed murine bone marrow-derived DCs was analyzed by cytokine production and stimulation of T-cell proliferation. The effect of VacA, CagA, transforming growth factor-beta (TGF-beta), and IL-10 on Th17/Treg balance was assessed. The in vivo significance of Tregs on the H pylori-specific Th17 response and H pylori density was determined by using anti-CD25 neutralizing antibodies to deplete Tregs in mice.

RESULTS

We showed that mucosal CD11c(+) DCs are located near the surface of normal gastric epithelium, and their number increased after H pylori infection. Study of the direct interaction of DCs with H pylori showed a Treg-skewed response. The Treg skewing was independent of H pylori VacA and CagA and dependent on TGF-beta and IL-10. In vivo Treg skewing by adoptive transfer of H pylori-pulsed DCs reduces the ratio of gastric IL-17/Foxp3 mRNA expressions. The depletion of CD25(+) Tregs results in early reduction of H pylori density, which is correlated with enhanced peripheral H pylori-specific Th17, but not Th1, response.

CONCLUSIONS

Overall, our study indicates that H pylori alters the DC-polarized Th17/Treg balance toward a Treg-biased response, which suppresses the effective induction of H pylori-specific Th17 immunity.

Helicobacter pylori oipA, vacA and dupA genetic diversity in individual hosts

Helicobacter pylori putative virulence factors can undergo a continuously evolving mechanism as an approach to bacterial adaptation to the host changing environment during chronic infection. oipA, vacA and dupA genetic diversity among isolates from multiple biopsies (niches) from the antrum and corpus of 40 patients was investigated. A set of 229 isolates was examined. Direct DNA sequence analysis of amplified fragments was used to study oipA 'on/off' expression status as well as the presence of C or T insertion in jhp0917 that originates a continuous (jhp0917-jhp0918) dupA gene. vacA alleles were identified by multiplex PCR. Different inter-niches oipA CT repeat patterns were observed in nine patients; in six of these, 'on' and 'off' mixed patterns were found. In three of these nine patients, different vacA alleles were also observed in a single host. Inter-niche dupA differences involved the absence and presence of jhp0917 and/or jhp0918 or mutations in dupA, including those that may originate a non-functional gene, and they were also present in two patients with mixed oipA CT patterns and in another seven patients. Evidence of mixed infection was observed in two patients only. In conclusion, oipA and dupA genes showed similar inter-niche variability, occurring in approximately 1/4 patients. Conversely, vacA allele microevolution seemed to be a less common event, occurring in approximately 1/10 patients, probably due to the mechanism that this gene evolves 'in vivo'.

Phosphonate metabolism in Helicobacter pylori

Helicobacter pylori has been shown to degrade two phosphonates, N-phosphonoacetyl-L: -aspartate and phosphonoacetate; however, the bacterium does not have any genes homologous to those of the known phosphonate metabolism pathways suggesting that H. pylori may have a novel phosphonate metabolism pathway. Growth of H. pylori on phosphonates was studied and the catabolism of these compounds was measured employing (1)H-nuclear magnetic resonance spectroscopy. The specificity of the catabolic enzymes was elucidated by assaying the degradation of several phosphonates and through substrate competition studies. H. pylori was able to utilise phenylphosphonate as a sole source of phosphate for growth. Three strains of H. pylori showed sigmoidal enzyme kinetics of phenylphosphonate catabolism. Allosteric kinetics were removed when lysates were fractionated into cytosolic and membrane fractions. Catabolic rates increased with the addition of DTT, Mg(2+) and phosphate and decreased with the addition of EDTA. The physiological properties of H. pylori phosphonate metabolism were characterised and the presence of at least two novel phosphonate catabolism pathways that do not require phosphate starvation growth conditions for activity has been established.

Lipopolysaccharide diversity evolving in Helicobacter pylori communities through genetic modifications in fucosyltransferases

Helicobacter pylori persistently colonizes the gastric mucosa of half the human population. It is one of the most genetically diverse bacterial organisms and subvariants are continuously emerging within an H. pylori population. In this study we characterized a number of single-colony isolates from H. pylori communities in various environmental settings, namely persistent human gastric infection, in vitro bacterial subcultures on agar medium, and experimental in vivo infection in mice. The lipopolysaccharide (LPS) O-antigen chain revealed considerable phenotypic diversity between individual cells in the studied bacterial communities, as demonstrated by size variable O-antigen chains and different levels of Lewis glycosylation. Absence of high-molecular-weight O-antigen chains was notable in a number of experimentally passaged isolates in vitro and in vivo. This phenotype was not evident in bacteria obtained from a human gastric biopsy, where all cells expressed high-molecular-weight O-antigen chains, which thus may be the preferred phenotype for H. pylori colonizing human gastric mucosa. Genotypic variability was monitored in the two genes encoding α1,3-fucosyltransferases, futA and futB, that are involved in Lewis antigen expression. Genetic modifications that could be attributable to recombination events within and between the two genes were commonly detected and created a diversity, which together with phase variation, contributed to divergent LPS expression. Our data suggest that the surrounding environment imposes a selective pressure on H. pylori to express certain LPS phenotypes. Thus, the milieu in a host will select for bacterial variants with particular characteristics that facilitate adaptation and survival in the gastric mucosa of that individual, and will shape the bacterial community structure.

The role of viral and bacterial pathogens in gastrointestinal cancer

The association of Helicobacter pylori (H. pylori) with gastric cancer is thus far the best understood model to comprehend the causal relationship between a microbial pathogen and cancer in the human gastrointestinal tract. Besides H. pylori, a variety of other pathogens are now being recognized as potential carcinogens in different settings of human cancer. In this context, viral causes of human cancers are central to the issue since these account for 10-20% of cancers worldwide. In the case of H. pylori and gastric cancer, as well as the human papillomavirus and anal cancer, the causal relationship between the infectious agent and the related cancer in the gastrointestinal tract has been clearly confirmed by epidemiological and experimental studies. Similarly, Epstein-Barr virus and the oncogenic JC virus are being suggested as possible causative agents for cancers in the upper and lower gastrointestinal tract. This review discusses various viral and microbial pathogens and their oncogenic properties in the evolution of gastrointestinal carcinogenesis and summarizes the available experimental data make a convincing agreement favoring the associations between infectious agents and specific human cancers.

Phenylphosphonate transport by Helicobacter pylori

BACKGROUND

Helicobacter pylori can utilize phenylphosphonate as a sole source of phosphorus, and it is able to transport the phosphonate N-phosphonoacetyl-L-aspartate. However, H. pylori does not have any genes homologous to those of the known pathways for phosphonate degradation in bacteria, indicating that it must have novel pathways for the transport and metabolism of phosphonates.

METHODS

Phenylphosphonate transport by H. pylori was studied in strains LC20, J99 and N6 by the centrifugation through oil method using [(14)C]-labeled phenylphosphonate.

RESULTS

The Michaelis constants of transport K(t) and V(max) for phenylphosphonate showed similar kinetics in the three strains. The Arrhenius plot for phenylphosphonate transport rates at permeant concentrations of 50 micromol/L was linear over the temperature range 10-40 degrees C with an activation energy of 3.5 kJ/mol, and a breakpoint between 5 and 10 degrees C. Transport rates increased with monovalent cation size. The effects of various inhibitors were investigated: iodoacetamide, amiloride, valinomycin, and nigericin reduced the rate of phenylphosphonate transport; sodium azide and sodium cyanide increased the transport rate; and monensin had no effect.

CONCLUSIONS

The kinetics and properties of H. pylori phenylphosphonate transport were characterized, and the data suggested a carrier-mediated transport mechanism.

Ten years after the first Helicobacter pylori genome: comparative and functional genomics provide new insights in the variability and adaptability of a persistent pathogen

In this review, we summarize how genomic approaches contributed to the understanding of the biology of the recently discovered pathogen Helicobacter pylori. Comparative genomics provided new insights into H. pylori's spectacular genetic diversity and generated exiting hypotheses on its evolutionary history. Transcriptomic studies provided original information on the mechanisms of H. pylori gastric adaptation that are central to its virulence.

Bacterial factors that mediate colonization of the stomach and virulence of Helicobacter pylori

Helicobacter pylori is a Gram-negative microaerophilic organism that colonizes the gastric mucosa of humans. Helicobacter pylori is one of the most common infections in humans and results in the development of gastritis in all infected individuals, although the majority of people are asymptomatic. A subset of infected people develop serious disease including duodenal ulceration and gastric cancer. Helicobacter pylori exhibits many striking characteristics. It lives in the hostile environment of the stomach and displays a very strict host and tissue tropism. Despite a vigorous immune response, infection persists for the lifetime of the host unless eradicated with antimicrobials. Why H. pylori is so pathogenic in some individuals and not in others is unknown but is thought to be due to a variety of host, environmental and bacterial factors. In this review, some of the bacterial factors that mediate colonization of the gastric mucosa and play a role in the pathogenesis of this organism have been considered.

Low concentrations of zinc in gastric mucosa are associated with increased severity of Helicobacter pylori-induced inflammation

BACKGROUND

Chronic Helicobacter pylori infection is the most common cause of gastric cancer. H. pylori induces oxidative stress while zinc deficiency results in increased sensitivity to it. In Ecuador, the prevalence of gastric cancer and zinc deficiency are high. We hypothesized that zinc deficiency in Ecuadorian people would cause increased H. pylori-induced inflammation in the gastric mucosa associated with lower tissue zinc concentrations.

METHODS

Three hundred and fifty-two patients with dyspepsia underwent endoscopy to obtain gastric mucosa biopsies. Diagnosis of H. pylori infection and its severity, histopathology, mucosal zinc concentration, and inflammation intensity were determined.

RESULTS

H. pylori-infected patients with non-atrophic chronic gastritis had lower concentrations of zinc in gastric mucosa than uninfected patients with the same type of gastritis (251.3 +/- 225.3 vs. 426.2 +/- 279.9 ng/mg of protein; p = .016). Considering all patients, the more severe the H. pylori infection, the higher the percentage of subjects with infiltration by polymorphonuclear (PMN) cells (p = .0001). Patients with high PMN infiltration had lower mucosal zinc concentrations than patients with low PMN infiltration (35.2 +/- 20.7 vs. 242.9 +/- 191.8 ng/mg of protein; p = .021).

CONCLUSIONS

The degree of inflammation in H. pylori-induced gastritis appears to be modulated by gastric tissue zinc concentrations.

Persistent bacterial infections and primary immune disorders

Mycobacteria, Salmonella and Helicobacter species have all evolved mechanisms to evade host defenses and cause persistent infection in humans. Host control of mycobacteria and Salmonella is largely achieved by the IFN-gamma/IL-12 pathway. Immune disorders affecting this pathway are characterized by disseminated infections with environmental or nontuberculous mycobacteria. Helicobacter is a predominantly extracellular bacterium that uses its remarkable genetic diversity (as well as other mechanisms) in order to evade host defenses. The importance of humoral immunity in containing Helicobacter infections to the mucosal surface is illustrated by the primary immune disorder, X-linked agammaglobulinemia in which patients are prone to chronic bacteremia and skin infections by Helicobacter and related species such as Flexispira and Campylobacter. Exploration of these particular infections in their specific immune defects sheds light on both host and bacterial mechanisms that have implications for pathogenesis and therapy.

Early-life family structure and microbially induced cancer risk

BACKGROUND

Cancer may follow exposure to an environmental agent after many decades. The bacterium Helicobacter pylori, known to be acquired early in life, increases risk for gastric adenocarcinoma, but other factors are also important. In this study, we considered whether early-life family structure affects the risk of later developing gastric cancer among H. pylori+ men.

METHODS AND FINDINGS

We examined a long-term cohort of Japanese-American men followed for 28 y, and performed a nested case-control study among those carrying H. pylori or the subset carrying the most virulent cagA+ H. pylori strains to address whether family structure predicted cancer development. We found that among the men who were H. pylori+ and/or cagA+ (it is possible to be cagA+ and H. pylori- if the H. pylori test is falsely negative), belonging to a large sibship or higher birth order was associated with a significantly increased risk of developing gastric adenocarcinoma late in life. For those with cagA+ strains, the risk of developing gastric cancer was more than twice as high (odds ratio 2.2; 95% confidence interval 1.2-4.0) among those in a sibship of seven or more individuals than in a sibship of between one and three persons.

CONCLUSIONS

These results provide evidence that early-life social environment plays a significant role in risk of microbially induced malignancies expressing five to eight decades later, and these findings lead to new models to explain these interactions.

Chronic exposure to Helicobacter pylori impairs dendritic cell function and inhibits Th1 development

Helicobacter pylori causes chronic gastric infection that affects the majority of the world's population. Despite generating an inflammatory response, the immune system usually fails to clear the infection. Since dendritic cells (DCs) play a pivotal role in shaping the immune response, we investigated the effects of H. pylori on DC function. We have demonstrated that H. pylori increased the expression of activation markers on DCs while upregulating the inhibitory B7 family molecule, PD-L1. Functionally, H. pylori-treated DCs resulted in the production of interleukin-10 (IL-10) and IL-23 but not of alpha interferon (IFN-alpha). While very little or no IL-12 was produced to H. pylori alone, simultaneous ligation of CD40 on DCs induced IL-12 release. We also demonstrated that DCs treated with H. pylori-induced IFN-gamma production by allogeneic naive T cells. However, stimulation of DCs with H. pylori for an extended period of time impaired their ability to produce cytokines after CD40 ligation and limited their ability to promote IFN-gamma release, suggesting that the DCs had become exhausted by the prolonged stimulation. The effect of chronic infection with H. pylori on DC function was further investigated by focusing on DC development. Demonstrating that monocytes differentiated into DCs in the presence of H. pylori exhibited an exhausted phenotype with an impaired ability to produce IL-12 and a downregulation of CD1a. Our results raise the possibility that in chronic H. pylori infection DCs become exhausted after prolonged antigen exposure leading to suboptimal Th1 development. This effect may contribute to persistence of H. pylori infection.

Mechanisms of disease: Helicobacter pylori-related gastric carcinogenesis--implications for chemoprevention

Gastric adenocarcinoma is the second most common cause of cancer-related mortality worldwide. Infection with Helicobacter pylori is the single most common cause of adenocarcinoma of the distal stomach. Cancer risk is believed to be related to differences among H. pylori strains and inflammatory responses governed by host genetics. In particular, specific interactions between host factors that modulate the response to the infection, and bacterial virulence factors that can directly cause tissue damage seem to have a major pathogenic role in the development of gastric cancer. In addition, environmental factors can modify key growth signaling pathways within the gastric mucosa, which leads to the alteration of epithelial cell growth. Preventive strategies represent the most promising means of decreasing cancer risk, and must be aimed at the control of H. pylori infection, improvement of environmental conditions, and the identification of subjects who are genetically predisposed to the development of cancer in response to H. pylori infection. Understanding the intracellular signaling pathways that are specifically affected by H. pylori and that promote phenotypic and genotypic changes that might ultimately progress to malignant transformation could enable physicians to focus eradication therapy appropriately and design interventions targeted at the molecular level to prevent the development of gastric cancer.

Antimutator role of the DNA glycosylase mutY gene in Helicobacter pylori

Helicobacter pylori has a highly variable genome with ongoing diversification via inter- and intragenomic recombination and spontaneous mutation. DNA repair genes modulating mutation and recombination rates that influence diversification have not been well characterized for H. pylori. To examine the role of putative base excision repair ung and mutY glycosylase and xthA apurinic/apyrimidinic endonuclease genes in H. pylori, mutants of each were constructed in strain JP26 by allelic exchange. Spontaneous mutation frequencies of JP26 mutY mutants, assessed by rifampin resistance, were consistently higher (26-fold) than that of the wild type, whereas the ung and xthA mutants showed smaller increases. In trans complementation of the JP26 mutY mutant restored spontaneous mutation frequencies to wild-type levels. In cross-species studies, H. pylori mutY complemented an Escherichia coli mutY mutant and vice versa. In contrast, the ung and mutY mutants did not show higher frequencies of intergenomic recombination or greater sensitivity to UV-induced DNA damage than the wild type. The H. pylori mutY open reading frame contains an eight-adenine homonucleotide tract; we provide evidence that this is subject to slipped-strand mispairing, leading to frameshifts that eliminate gene function. Our findings indicate that H. pylori possesses phase-variable base excision repair, consistent with a tension between repair and mutation.

The complete genome sequence of a chronic atrophic gastritis Helicobacter pylori strain: evolution during disease progression

Helicobacter pylori produces acute superficial gastritis in nearly all of its human hosts. However, a subset of individuals develops chronic atrophic gastritis (ChAG), a condition characterized in part by diminished numbers of acid-producing parietal cells and increased risk for development of gastric adenocarcinoma. Previously, we used a gnotobiotic transgenic mouse model with an engineered ablation of parietal cells to show that loss of parietal cells provides an opportunity for a H. pylori isolate from a patient with ChAG (HPAG1) to bind to, enter, and persist within gastric stem cells. This finding raises the question of how ChAG influences H. pylori genome evolution, physiology, and tumorigenesis. Here we describe the 1,596,366-bp HPAG1 genome. Custom HPAG1 Affymetrix GeneChips, representing 99.6% of its predicted ORFs, were used for whole-genome genotyping of additional H. pylori ChAG isolates obtained from Swedish patients enrolled in a case-control study of gastric cancer, as well as ChAG- and cancer-associated isolates from an individual who progressed from ChAG to gastric adenocarcinoma. The results reveal a shared gene signature among ChAG strains, as well as genes that may have been lost or gained during progression to adenocarcinoma. Whole-genome transcriptional profiling of HPAG1's response to acid during in vitro growth indicates that genes encoding components of metal uptake and utilization pathways, outer membrane proteins, and virulence factors are among those associated with H. pylori's adaptation to ChAG.

Interactions between gastric epithelial stem cells and Helicobacter pylori in the setting of chronic atrophic gastritis

Chronic atrophic gastritis (ChAG), a Helicobacter pylori-associated risk factor for the development of gastric cancer, involves loss of acid-producing parietal cells. Recent studies in gnotobiotic mouse models of ChAG have shown that parietal cell loss results in amplification of multi- and oligo-potential gastric stem cells that express sialylated glycan receptors recognized by H. pylori adhesins. Moreover, H. pylori resides within a subset of these stem cells. Studies of the transcriptomes of gastric stem cells, harvested directly from the stomachs of uninfected mice, using laser capture microdissection, suggest that they have the ability to complement some of the metabolic needs of H. pylori. These findings indicate that proliferating and non-proliferating gastric stem cells provide a habitat that could support H. pylori persistence in a gastric ecosystem that has lost its acid barrier to colonization by environmental, oral and intestinal microbes. One consequence to the host might be an increased risk of tumorigenesis.

Helicobacter infection and gastric neoplasia

Chronic gastritis induced by Helicobacter pylori is the strongest known risk factor for adenocarcinoma of the distal stomach, yet only a minority of people who harbour this organism ever develop cancer. H. pylori isolates possess substantial genotypic diversity, which engenders differential host inflammatory responses that influence clinical outcome. H. pylori strains that possess the cag pathogenicity island and secrete a functional cytotoxin induce more severe gastric injury and further augment the risk for developing distal gastric cancer. However, carcinogenesis is also influenced by host genetic diversity, particularly involving immune response genes such as IL-1ss and TNF-alpha. It is important to gain insight into the pathogenesis of H. pylori-induced gastritis and adenocarcinoma, not only to develop more effective treatments for gastric cancer, but also because it might serve as a paradigm for the role of chronic inflammation in the genesis of other malignancies that arise within the gastrointestinal tract.