Sterilizing immunity against experimental Helicobacter pylori infection is challenge-strain dependent

Review: Helicobacter: Inflammation, immunology, and vaccines

Chronic inflammation induced by Helicobacter pylori infection is a critical factor in the development of peptic ulcer disease and gastric cancer. Central to this inflammation is the initiation of pro-inflammatory signaling cascades within epithelial cells, in particular those mediated by two sensors of bacterial cell wall components, nucleotide-binding oligomerization domain-containing protein 1 (NOD1) and alpha-protein kinase 1 (ALPK1). H pylori is, however, also highly adept at mitigating inflammation in the host, thereby restricting tissue damage and favoring bacterial persistence. H pylori modulates host immune responses by altering cytokine signaling in epithelial and myeloid cells, which results in increased proliferation of regulatory T cells and downregulation of effector T-cell responses. H pylori vacuolating cytotoxin A (VacA) has been shown to play an important role in the dampening of immune responses and induction of immune tolerance capable of protecting against asthma. It is also possible to generate protective immune responses by immunization with various H pylori antigens or their epitopes, in combination with an adjuvant, though this for now has only been shown in mouse models. Novel non-toxic adjuvants, consisting of modified bacterial enterotoxins or nanoparticles, have recently been developed that may not only enhance vaccine efficacy, but also help translate candidate vaccines to the clinic. This review will summarize the main discoveries in the past year regarding host immune responses to H pylori infection, as well as the design of new vaccine approaches against this infection.

Pathogenicity of Helicobacter pylori in cancer development and impacts of vaccination

Helicobacter pylori affect around 50% of the population worldwide. More importantly, the gastric infection induced by this bacterium is deemed to be associated with the progression of distal gastric carcinoma and gastric mucosal lymphoma in the human. H. pylori infection and its prevalent genotype significantly differ across various geographical regions. Based on numerous virulence factors, H. pylori can target different cellular proteins to modulate the variety of inflammatory responses and initiate numerous "hits" on the gastric mucosa. Such reactions lead to serious complications, including gastritis and peptic ulceration, gastric cancer and gastric mucosa-associated lymphoid structure lymphoma. Therefore, H. pylori have been considered as the type I carcinogen by the Global Firm for Research on Cancer. During the two past decades, different reports revealed that H. pylori possess oncogenic potentials in the gastric mucosa through a complicated interplay between the bacterial factors, various facets, and the environmental factors. Accordingly, numerous signaling pathways could be triggered in the development of gastrointestinal diseases (e.g., gastric cancer). Therefore, the main strategy for the treatment of gastric cancer is controlling the disease far before its onset using preventive/curative vaccination. Increasing the efficiency of vaccines may be achieved by new trials of vaccine modalities, which is used to optimize the cellular immunity. Taken all, H. pylori infection may impose severe complications, for resolving of which extensive researches are essential in terms of immune responses to H. pylori. We envision that H. pylori-mediated diseases can be controlled by advanced vaccines and immunotherapies.

Structural and functional insight into serine hydroxymethyltransferase from Helicobacter pylori

Serine hydroxymethyltransferase (SHMT), encoded by the glyA gene, is a ubiquitous pyridoxal 5'-phosphate (PLP)-dependent enzyme that catalyzes the formation of glycine from serine. The thereby generated 5,10-methylene tetrahydrofolate (MTHF) is a major source of cellular one-carbon units and a key intermediate in thymidylate biosynthesis. While in virtually all eukaryotic and many bacterial systems thymidylate synthase ThyA, SHMT and dihydrofolate reductase (DHFR) are part of the thymidylate/folate cycle, the situation is different in organisms using flavin-dependent thymidylate synthase ThyX. Here the distinct catalytic reaction directly produces tetrahydrofolate (THF) and consequently in most ThyX-containing organisms, DHFR is absent. While the resulting influence on the folate metabolism of ThyX-containing bacteria is not fully understood, the presence of ThyX may provide growth benefits under conditions where the level of reduced folate derivatives is compromised. Interestingly, the third key enzyme implicated in generation of MTHF, serine hydroxymethyltransferase (SHMT), has a universal phylogenetic distribution, but remains understudied in ThyX-containg bacteria. To obtain functional insight into these ThyX-dependent thymidylate/folate cycles, we characterized the predicted SHMT from the ThyX-containing bacterium Helicobacter pylori. Serine hydroxymethyltransferase activity was confirmed by functional genetic complementation of a glyA-inactivated E. coli strain. A H. pylori ΔglyA strain was obtained, but exhibited markedly slowed growth and had lost the virulence factor CagA. Biochemical and spectroscopic evidence indicated formation of a characteristic enzyme-PLP-glycine-folate complex and revealed unexpectedly weak binding affinity of PLP. The three-dimensional structure of the H. pylori SHMT apoprotein was determined at 2.8Ǻ resolution, suggesting a structural basis for the low affinity of the enzyme for its cofactor. Stabilization of the proposed inactive configuration using small molecules has potential to provide a specific way for inhibiting HpSHMT.

Iron-sulfur protein maturation in Helicobacter pylori: identifying a Nfu-type cluster carrier protein and its iron-sulfur protein targets

Helicobacter pylori is anomalous among non nitrogen-fixing bacteria in containing an incomplete NIF system for Fe-S cluster assembly comprising two essential proteins, NifS (cysteine desulfurase) and NifU (scaffold protein). Although nifU deletion strains cannot be obtained via the conventional gene replacement, a NifU-depleted strain was constructed and shown to be more sensitive to oxidative stress compared to wild-type (WT) strains. The hp1492 gene, encoding a putative Nfu-type Fe-S cluster carrier protein, was disrupted in three different H. pylori strains, indicating that it is not essential. However, Δnfu strains have growth deficiency, are more sensitive to oxidative stress and are unable to colonize mouse stomachs. Moreover, Δnfu strains have lower aconitase activity but higher hydrogenase activity than the WT. Recombinant Nfu was found to bind either one [2Fe-2S] or [4Fe-4S] cluster/dimer, based on analytical, UV-visible absorption/CD and resonance Raman studies. A bacterial two-hybrid system was used to ascertain interactions between Nfu, NifS, NifU and each of 36 putative Fe-S-containing target proteins. Nfu, NifS and NifU were found to interact with 15, 6 and 29 putative Fe-S proteins respectively. The results indicate that Nfu, NifS and NifU play a major role in the biosynthesis and/or delivery of Fe-S clusters in H. pylori.

The redefinition of Helicobacter pylori lipopolysaccharide O-antigen and core-oligosaccharide domains

Helicobacter pylori lipopolysaccharide promotes chronic gastric colonisation through O-antigen host mimicry and resistance to mucosal antimicrobial peptides mediated primarily by modifications of the lipid A. The structural organisation of the core and O-antigen domains of H. pylori lipopolysaccharide remains unclear, as the O-antigen attachment site has still to be identified experimentally. Here, structural investigations of lipopolysaccharides purified from two wild-type strains and the O-antigen ligase mutant revealed that the H. pylori core-oligosaccharide domain is a short conserved hexasaccharide (Glc-Gal-DD-Hep-LD-Hep-LD-Hep-KDO) decorated with the O-antigen domain encompassing a conserved trisaccharide (-DD-Hep-Fuc-GlcNAc-) and variable glucan, heptan and Lewis antigens. Furthermore, the putative heptosyltransferase HP1284 was found to be required for the transfer of the third heptose residue to the core-oligosaccharide. Interestingly, mutation of HP1284 did not affect the ligation of the O-antigen and resulted in the attachment of the O-antigen onto an incomplete core-oligosaccharide missing the third heptose and the adjoining Glc-Gal residues. Mutants deficient in either HP1284 or O-antigen ligase displayed a moderate increase in susceptibility to polymyxin B but were unable to colonise the mouse gastric mucosa. Finally, mapping mutagenesis and colonisation data of previous studies onto the redefined organisation of H. pylori lipopolysaccharide revealed that only the conserved motifs were essential for colonisation. In conclusion, H. pylori lipopolysaccharide is missing the canonical inner and outer core organisation. Instead it displays a short core and a longer O-antigen encompassing residues previously assigned as the outer core domain. The redefinition of H. pylori lipopolysaccharide domains warrants future studies to dissect the role of each domain in host-pathogen interactions. Also enzymes involved in the assembly of the conserved core structure, such as HP1284, could be attractive targets for the design of new therapeutic agents for managing persistent H. pylori infection causing peptic ulcers and gastric cancer.

Helicobacter Catalase Devoid of Catalytic Activity Protects the Bacterium against Oxidative Stress

Catalase, a conserved and abundant enzyme found in all domains of life, dissipates the oxidant hydrogen peroxide (H₂O₂). The gastric pathogen Helicobacter pylori undergoes host-mediated oxidant stress exposure, and its catalase contains oxidizable methionine (Met) residues. We hypothesized catalase may play a large stress-combating role independent of its classical catalytic one, namely quenching harmful oxidants through its recyclable Met residues, resulting in oxidant protection to the bacterium. Two Helicobacter mutant strains (katA^H56A and katA^Y339A) containing catalase without enzyme activity but that retain all Met residues were created. These strains were much more resistant to oxidants than a catalase-deletion mutant strain. The quenching ability of the altered versions was shown, whereby oxidant-stressed (HOCl-exposed) Helicobacter retained viability even upon extracellular addition of the inactive versions of catalase, in contrast to cells receiving HOCl alone. The importance of the methionine-mediated quenching to the pathogen residing in the oxidant-rich gastric mucus was studied. In contrast to a catalase-null strain, both site-change mutants proficiently colonized the murine gastric mucosa, suggesting that the amino acid composition-dependent oxidant-quenching role of catalase is more important than the well described H₂O₂-dissipating catalytic role. Over 100 years after the discovery of catalase, these findings reveal a new non-enzymatic protective mechanism of action for the ubiquitous enzyme.

Current Status and Prospects for a Helicobacter pylori Vaccine

Helicobacter pylori infection contributes to a variety of gastric diseases. H pylori-associated gastric cancer is diagnosed in advanced stages, and a vaccine against H pylori is desirable in parts of the world where gastric cancer remains a common form of cancer. Some of the strategies of vaccine development used in animals have been tested in several phase 3 clinical trials; these trials have been largely unsuccessful, although H pylori-specific immune responses have been induced. New insights into promoting immunity and overcoming the immunosuppressive nature of H pylori infection are required to improve the efficacy of an H pylori vaccine.

Vaccinating against Helicobacter pylori in the developing world

Helicobacter pylori infects more than half the world's population and in developing nations the incidence can be over 90%. The morbidity and mortality associated with H. pylori-associated diseases including ulcers and gastric cancer therefore, disproportionately impact the developing world. Mice have been used extensively to demonstrate the feasibility of developing a vaccine for H. pylori infection, and for testing antigens, routes of immunization, dose, and adjuvants. These successes however, have not translated well in clinical trials. Although there are examples where immune responses have been activated, there are few instances of achieving a reduced bacterial load. In vivo and in vitro analyses in both mice and humans demonstrates that the host responds to H. pylori infection through the activation of immunoregulatory mechanisms designed to suppress the anti-H. pylori response. Improved vaccine efficacy therefore, will require the inclusion of factors that over-ride or re-program these immunoregulatory rersponse mechanisms.

In silico experiment with an-antigen-toll like receptor-5 agonist fusion construct for immunogenic application to Helicobacter pylori

BACKGROUNDS

Helicobacter pylori colonize the gastric mucosa of half of the world's population. Although it is classified as a definitive type I carcinogen by World Health Organization, there is no effective vaccine against this bacterium. H. pylori evade the host immune response by avoiding toll-like detection, such as detection via toll-like receptor-5 (TLR-5). Thus, a chimeric construct consisting of selected epitopes from virulence factors that is incorporated into a TLR-5 ligand (Pseudomonas flagellin) could result in more potent innate and adaptive immune responses.

MATERIALS AND METHODS

Based on the histocompatibility antigens of BALB/c mice, in silico techniques were used to select several fragments from H. pylori virulence factors with a high density of B- and T-cell epitopes.

RESULTS

These segments consist of cytotoxin-associated geneA (residue 162-283), neutrophil activating protein (residue 30-135) and outer inflammatory protein A (residue 155-268). The secondary and tertiary structure of the chimeric constructs and other bioinformatics analyses such as stability, solubility, and antigenicity were performed. The chimeric construct containing antigenic segments of H. pylori proteins was fused with the D3 domain of Pseudomonas flagellin. This recombinant chimeric gene was optimized for expression in Escherichia coli. The in silico results showed that the conserved C- and N-terminal domains of flagellin and the antigenicity of selected fragments were retained.

DISCUSSION

In silico analysis showed that Pseudomonas flagellin is a suitable platform for incorporation of an antigenic construct from H. pylori. This strategy may be an effective tool for the control of H. pylori and other persistent infections.

Xer-cise in Helicobacter pylori: one-step transformation for the construction of markerless gene deletions

BACKGROUND

Xer-cise is an efficient selectable marker removal technique that was first applied in Bacillus subtilis and Escherichia coli for the construction of markerless gene deletions. Xer-cise marker excision takes advantage of the presence of site-specific Xer recombination in most bacterial species for the resolution of chromosome dimers at the dif site during replication. The identification and functional characterization of the difH/XerH recombination system enabled the development of Xer-cise in Helicobacter pylori.

METHODS

Markerless deletions were obtained by a single natural transformation step of the Xer-cise cassette containing rpsL and cat genes, for streptomycin susceptibility and chloramphenicol resistance respectively, flanked by difH sites and neighboring homologous sequences of the target gene. Insertion/deletion recombinant H. pylori were first selected on chloramphenicol-containing medium followed by selection on streptomycin-containing medium for clones that underwent XerH mediated excision of the rpsL-cat cassette, resulting in a markerless deletion.

RESULTS

XerH-mediated removal of the antibiotic marker was successfully applied in three different H. pylori strains to obtain markerless gene deletions at very high efficiencies. An unmarked triple deletion mutant was also constructed by sequential deletion of ureA, vacA and HP0366 and removal of the selectable marker at each step. The triple mutant had no growth defect suggesting that multiple difH sites per chromosome can be tolerated without affecting bacterial fitness.

CONCLUSION

Xer-cise eliminates the need for multiple passages on non selective plates and subsequent screening of clones for loss of the antibiotic cassette by replica plating.

Leptin, CD4(+) T(reg) and the prospects for vaccination against H. pylori infection

Helicobacter pylori infection induces chronic inflammation which is characterized not only by infiltrations of inflammatory cells such as neutrophils and CD4⁺ T cells, but also significant populations of regulatory T cells (T_reg). These cells are important for disease pathogenesis because they are believed to contribute to the persistence of the infection. Despite encouraging results in animal models, the prospects for an effective H. pylori vaccine are currently poor because of generally disappointing results in preclinical and phase 1 trials. As a result, a current major focus of basic research on vaccination is to better understand the mechanisms regulating the inflammatory response with the view it can inform future vaccine design. Our studies in this area have focused on gastric CD4⁺ T_reg in vaccinated mice, and raised the hypothesis that adipokines in particular leptin are involved the establishment of a protective gastric immune response. Here we discuss the hypothesis that vaccination deregulates T_reg responses in the gastric mucosa, and that this process is mediated by leptin. We propose that reduced suppression permits a protective sub population of H. pylori-specific CD4⁺ T cells to exert protective effects, presumably via the gastric epithelium. Evidence from the literature and experimental approaches will be discussed.

Possible correlates of long-term protection against Helicobacter pylori following systemic or combinations of mucosal and systemic immunizations

The ability to induce long-term immunity to Helicobacter pylori is necessary for an effective vaccine. This study was designed to establish the most efficient route(s) (systemic, mucosal, or a combination) of immunization for induction of long-term immunity and to define correlates of protection. Mice were immunized orally alone (oral group), intramuscularly (i.m.) alone (i.m. group), orally followed by i.m. (oral/i.m. group), or i.m. followed by orally (i.m./oral group). Long-term protective immunity to oral H. pylori challenge was observed 3 months after immunization through the i.m. or oral/i.m. route. Protection correlated with an increase in H. pylori-specific interleukin-12 and both immunoglobulin G1 (IgG1) and IgG2a serum titers following challenge. Mice that were not protected (oral or i.m./oral) had increased levels of IgA in both sera and Peyer's patches. This study demonstrates the ability to induce long-term immunity against H. pylori, provides correlates of protection, and illustrates the crucial role of the immunization route(s).

Novel methods of quantitative real-time PCR data analysis in a murine Helicobacter pylori vaccine model

Monitoring of Helicobacter pylori in the stomach is important to assess the efficacy of new vaccines against the pathogen. To realise the full potential of quantitative real-time PCR (q-PCR), this technology has to offer accurate and easy models of post-PCR data analysis. In this work, we used a variety of absolute and relative approaches of q-PCR data analysis to monitor the H. pylori infection in the stomach of immunized mice. Relative quantification was performed with Ct-based methods, with the DART program, and with two methods based on the mathematical analysis of raw fluorescence kinetics, the LinReg program and the Sigmoidal Curve Fitting Method. The different calculation methods were validated in mice immunized with cell lysates of Lactococcus lactis expressing the H. pylori urease subunit B in combination with cholera toxin. The H. pylori load was found to be reduced in immunized mice by a factor of 50-144, depending on the calculation method employed. We found that relative quantification using DART, LinReg and Sigmoidal Curve Fitting methods generated similar results (infection ratios of 54-58) with absolute quantification results (54-65). Results were very different to those using relative quantification Ct-based methods without a correction for PCR efficiency (ratio of 92-144) and with results based on conventional culture method (ratio of 34). Overall, this study demonstrates that q-PCR associated with a relative quantification analysis is a powerful tool for the monitoring of microorganisms in tissue. It could be used as an alternative to standard curve approach especially for the investigation of microbial load in vaccine models.

The inflammatory and immune response to Helicobacter pylori infection

Lifelong Helicobacter pylori infection and its associated gastric inflammation underlie peptic ulceration and gastric carcinogenesis. The immune and inflammatory responses to H. pylori are doubly responsible: gastric inflammation is the main mediator of pathology, and the immune and inflammatory response is ineffective, allowing lifelong bacterial persistence. However, despite inducing gastric inflammation, most infections do not cause disease, and bacterial, host and environmental factors determine individual disease risk. Although H. pylori avoids many innate immune receptors, specific virulence factors (including those encoded on the cag pathogenicity island) stimulate innate immunity to increase gastric inflammation and increase disease risk. An acquired T helper 1 response upregulates local immune effectors. The extent to which environmental factors (including parasite infection), host factors and H. pylori itself influence T-helper differentiation and regulatory T-cell responses remains controversial. Finally, effective vaccines have still not been developed: a better understanding of the immune response to H. pylori may help.

Helicobacter pylori cag-type IV secretion system facilitates corpus colonization to induce precancerous conditions in Mongolian gerbils

BACKGROUND & AIMS

Epidemiological studies suggest that atrophic corpus-dominant gastritis is an increased risk factor for gastric carcinogenesis. The role of the Helicobacter pylori type IV secretion system (T4SS) for pathogenesis in the Mongolian gerbil model was explored.

METHODS

Mongolian gerbils were infected for 32 weeks either with H. pylori type I strain B128 or with isogenic mutant strain B128delta cytotoxin-associated gene (cagY) or B128delta cagA , defective in T4SS or in the production of its effector protein CagA, respectively. Quantitative H. pylori reisolation was performed from the gastric antrum and corpus separately, cytokines were measured by quantitative reverse-transcription polymerase chain reaction, and gastric pH and hormones were determined.

RESULTS

B128-infected gerbils harbored high numbers of bacteria in the gastric antrum and corpus, whereas B128delta cagY and B128delta cagA colonized the antrum more densely than the corpus. All infected animals showed a strong antral inflammation and epithelial cell proliferation. B128-infected, rather than mutant-infected, gerbils presented a severe transmural inflammation with huge lymph aggregates, increased proliferation, significant atrophy, and mucous gland metaplasia in the corpus. Plasma gastrin levels and gastric pH values were significantly increased only in B128-infected gerbils. In all infected animals, the expression of the proinflammatory cytokines interleukin 1beta, interferon gamma, and growth-regulated protein was considerably increased in the antrum, but only in wild type-infected animals was an increase seen in the corpus mucosa.

CONCLUSIONS

The presence of an intact T4SS allows H. pylori to colonize the gastric corpus. This results in atrophic corpus-dominant gastritis, a severe precancerous condition, thus highlighting T4SS and CagA as major risk factors for gastric cancer development.

Systemic Th1 immunization of mice against Helicobacter pylori infection with CpG oligodeoxynucleotides as adjuvants does not protect from infection but enhances gastritis

Recent reports have suggested that oral vaccination of mice against Helicobacter pylori is dependent on a Th1-mediated immune response. However, oral vaccination in mice neither induces sterilizing immunity nor leads to complete protection from disease. Therefore, in this study we investigated whether a systemic subcutaneous immunization against H. pylori by using CpG oligodeoxynucleotides as a Th1 adjuvant could achieve protection in a mouse model of H. pylori infection. CpG oligodeoxynucleotides are known for their ability to induce nearly entirely Th1-biased immune responses and may be approved for human use in future. Immunization of mice with H. pylori lysate and CpG induced a strong local and systemic Th1 immune response. Despite this strong Th1 response, mice were not protected from infection with H. pylori yet had a 10-fold reduction in the number of H. pylori in the gastric mucosa compared to nonimmunized mice. Of note, reduction of the bacterial density in immunized mice was accompanied by a significantly enhanced gastritis. Hence, systemic Th1 immunization of mice, even though being able to reduce the bacterial load in the stomach, is associated with aggravated pathology.

Motility of urease-deficient derivatives of Helicobacter pylori

Early studies of a ureB mutant derivative of Helicobacter pylori had suggested that urease is needed for motility and that urease action helps energize flagellar rotation. Here we report experiments showing that motility is unaffected by deletion of ureA and ureB (urease genes) or by inactivation of ureB alone, especially if H. pylori strains used as recipients for transformation with mutant alleles are preselected for motility. This result was obtained with the strain used in the early studies (CPY3401) and also with 15 other strains, 3 of which can colonize mice. We conclude that urease is not needed for H. pylori motility.

Helicobacter pylori tissue tropism: mouse-colonizing strains can target different gastric niches

Studies with the mouse-adapted Helicobacter pylori strain SS1 had supported an idea that infections by this pathogen start in the gastric antrum and spread to the corpus after extensive mucosal damage. This paper shows that the unrelated strain X47 colonizes the corpus preferentially. Differences between strains in preferred gastric region were detected by co-inoculating mice with a mixture of SS1 and X47, and genotyping H. pylori recovered after 2-8 weeks of infection by vacA s allele PCR and RAPD fingerprinting. Mixed infections were found in each of 59 co-inoculated young C57BL/6J mice. On average, however, SS1 was fourfold more abundant than X47 in the antrum and X47 was threefold more abundant than SS1 in the corpus. Similar results were obtained in mice inoculated first with one strain and then the other strain 2 weeks later. SS1 was even more abundant in the antrum of elderly (>1 year old) mice (97 % of isolates). Qualitatively similar SS1 and X47 tissue distributions were seen using unrelated mouse lines (AKR/J, A/J, DBA/2J, BALB/cJ, LG/J, SM/J), but with significantly different SS1 : X47 ratios in some cases. These results suggest the existence of at least two distinct gastric niches whose characteristics may be affected by host genotype and age (physiology), and indicate that strains differ in how effectively they colonize each niche. Differences among gastric regions and the mixed infections that these allow may contribute to H. pylori diversity and genome evolution.

The quest for a vaccine against Helicobacter pylori: how to move from mouse to man?

Several lines of evidence from experimental animal models of infection have clearly demonstrated the feasibility of a prophylactic and therapeutic vaccine against Helicobacter pylori. However, comparatively few clinical studies have been carried out to evaluate whether the positive results obtained in animals can be reproduced in humans. The preliminary results obtained with single component, mucosally delivered vaccines have shown very limited results thus far. Very good immunogenicity and safety profiles are now being obtained with parenterally delivered, aluminium hydroxide-adjuvanted multicomponent candidate vaccines. For sure, better vaccine formulations, better antigen preparation(s), better adjuvants, and better delivery systems have to be designed and tested for safety and immunogenicity. These studies are also needed for deciphering those aspects of the effector immune responses that correlate with protection against H. pylori infection and disease.

Construction of clone expressing adhesin Hsp60 of Helicobacter pylori

AIM

To construct a recombinant vector containing gene encoding Hsp60 gene of Helicobacter pylori and to express the vector in E.coli BL21.

METHODS

The Hsp60 gene was amplified from H.pylori chromosome by PCR and inserted into the prokaryotie expression vector pET-22b (+). The recombinant vector was transformed and expressed in E.coli BL21 (DE3). Recombinant Hsp60 protein immunogenicity was studied by Western blot.

RESULTS

The 1.6 kb Hsp60 gene was successfully isolated. Recombinant E.coli strains expressed Hsp60 were obtained, the expression protein amounted to 27.2% of the total bacterial protein after induced with IPTG for 3 h at 37 ℃, which included inclusion body and soluble protein. Inclusion body was the major pattern of the expression that amounted to 76.6% of the insoluble protein. Western blot analysis of rHsp60 confirmed that it could be specially recognized by serum from Hp infected patients.

CONCLUSION

The gene coding for Hp Hsp60 is cloned and expressed successfully. The results obtained lay the foundation for constructing the H.pylori vaccine.

Helicobacter pylori inflammation and immunity

Gastric inflammation is a significant contributor to the disease process associated with Helicobacter pylori infection. It appears that both bacterial genes and differential host responses make interrelated contributions to gastritis and disease outcome after H. pylori infection. While the cag pathogenicity island (PAI) continues to be a focus for much of this investigation on the bacterial side, other bacterial genes/proteins are certainly important as well. On the host cell side, significant progress is being made defining the eucaryotic signaling cascades induced after host cells interact with H. pylori. The role of host cell cytokines, gastric acid, and mast cells is also being actively studied. Prospects for control of H. pylori associated disease continue to include vaccination. The mechanism(s) for vaccine-mediated control of H. pylori infection and disease remain ill-defined but recent evidence from animal models suggests that the inflammatory response may be involved. Manipulating the host response to H. pylori infection in humans to take advantage of the possible beneficial effects of inflammation, while minimizing its detrimental effects is a significant challenge for the future.

Clearance of Helicobacter pylori Infection and Resolution of Postimmunization Gastritis in a Kinetic Study of Prophylactically Immunized Mice

Patients infected with Helicobacter pylori mount an immune response which fails to clear the infection and may contribute to disease. Mice can be protected by immunization. To further characterize the H. pylori-mouse model, stomachs of unimmunized or intranasally immunized C57BL/6 mice were quantitatively cultured 3 days and 1, 2, 4, 8, 16, 32, and 52 weeks after challenge with H. pylori. At 3 days and 1 week after challenge, colonization was the same in the immunized and unimmunized mice. By 2 weeks after challenge, the immunized mice had a >2-log decrease in bacterial load, and at all later time points, they either were culture negative or had at least a 2-log decrease in bacterial load. Gastritis in the immunized mice peaked at 1 to 2 weeks after challenge and was characterized by a mixed inflammatory infiltrate and epithelial proliferation centered at the transition between corpus and antrum. By 52 weeks postchallenge, the gastric histology in the immunized mice was not different from that in control unchallenged mice. The unimmunized group began to show a reduction in bacterial load as early as 16 weeks after challenge, and by 52 weeks seven of eight unimmunized mice had developed gastritis and reduced bacterial loads. These results indicate that prophylactic immunization does not prevent colonization by H. pylori but enables mice to clear the infection or significantly reduce the number of colonizing bacteria. The reduction in bacterial load is associated with gastric inflammation that subsides over time.

Reduced activation of inflammatory responses in host cells by mouse-adapted Helicobacter pylory isolates

Helicobacter pylori strains that harbour the Cag pathogenicity island (Cag PAI) induce interleukin (IL)-8 secretion in gastric epithelial cells, via the activation of NF- kappa B, and are associated with severe inflammation in humans. To investigate the influence of Cag PAI-mediated inflammatory responses on H. pylori adaptation to mice, a selection of H. pylori clinical isolates (n = 12) was cag PAI genotyped and tested in co-culture assays with AGS gastric epithelial cells, and in mouse colonization studies. Six isolates were shown to harbour a complete cag PAI and to induce NF- kappa B activation and IL-8 secretion in AGS cells. Of the eight isolates that spontaneously colonized mice, six had a cag PAI(-) genotype and did not induce pro-inflammatory responses in these cells. Mouse-to-mouse passage of the two cag PAI(+) -colonizing strains yielded host-adapted variants that infected mice with bacterial loads 100-fold higher than those of the respective parental strains (P= 0.001). These mouse-adapted variants were affected in their capacity to induce pro-inflammatory responses in host cells, yet no changes in cag PAI gene content were detected between the strains by DNA microarray analysis. This work provides evidence for in vivo selection of H. pylori bacteria with a reduced capacity to induce inflammatory responses and suggests that such bacteria are better adapted to colonize mice.