Helicobacter pylori vaccine strategies--triggering a gut reaction

Helicobacter pylori induces urease subunit B-specific CD8+ T cell responses in infected individuals via cytosolic pathway of cross-presentation

BACKGROUND

Urease subunit B (UreB), a conserved and key virulence factor of Helicobacter pylori (H. pylori), can induce the host CD4+ T cell immune responses to provide protection, but less is known regarding CD8+ T cell responses. The characteristics of H. pylori-specific CD8+ T cell responses and the mechanism underlying antigen processing and presentation pathways remain unclear. This study was focus on protective antigen recombinant UreB (rUreb) to detect specific CD8+ T cell responses in vitro and elucidate the mechanism of UreB antigen processing and presentation.

METHODS

The peripheral blood mononuclear cells (PBMCs) collected from H. pylori-infected individuals were stimulated with rUreB in vitro to detect specific CD8+ T cell responses after co-culture with rUreB-pulsed autologous hMDCs. Through blocking assay, we investigated the potential pathway of UreB antigen processing and presentation via the cytosolic pathway or vacuolar pathway. The cytokines production of UreB specific CD8+ T cell were evaluated as well.

RESULTS

We demonstrated UreB can induce specific CD8+ T cell immune responses in H. pylori infected individuals. Importantly, we characterized that UreB were mainly processed by proteasome instead of lysosomal proteases and presented through cytosolic pathway of cross-presentation, which requires endoplasmic reticulum-Golgi transport and newly synthesized MHC-I molecules, to induce functional-specific CD8+ T cell (IFN-γ + TNF-α + Grz A+ Grz B+) responses.

CONCLUSIONS

These results suggest that H. pylori UreB induces specific CD8+ T cell responses through cytosolic pathway of cross-presentation in infected individuals.

Designing and development of epitope-based vaccines against Helicobacter pylori

Helicobacter pylori infection is the principal cause of serious diseases (e.g. gastric cancer and peptic ulcers). Antibiotic therapy is an inadequate strategy in H. pylori eradication because of which vaccination is an inevitable approach. Despite the presence of countless vaccine candidates, current vaccines in clinical trials have performed with poor efficacy which makes vaccination extremely challenging. Remarkable advancements in immunology and pathogenic biology have provided an appropriate opportunity to develop various epitope-based vaccines. The fusion of proper antigens involved in different aspects of H. pylori colonization and pathogenesis as well as peptide linkers and built-in adjuvants results in producing epitope-based vaccines with excellent therapeutic efficacy and negligible adverse effects. Difficulties of the in vitro culture of H. pylori, high genetic variation, and unfavourable immune responses against feeble epitopes in the complete antigen are major drawbacks of current vaccine strategies that epitope-based vaccines may overcome. Besides decreasing the biohazard risk, designing precise formulations, saving time and cost, and induction of maximum immunity with minimum adverse effects are the advantages of epitope-based vaccines. The present article is a comprehensive review of strategies for designing and developing epitope-based vaccines to provide insights into the innovative vaccination against H. pylori.

How far are we from vaccination against Helicobacter pylori infection?

INTRODUCTION

Helicobacter pylori infection results in chronic gastritis, peptic ulcer, or gastric cancer; therefore, eradication of this bacterium is essential. The strategy for developing effective vaccines against H. pylori entails immunization of mice with a combination of classical and recombinant H. pylori antigens, but this has proven to be onerous in all cases.

AREAS COVERED

We have reviewed literature databases in PubMed and Scopus using the key words H. pylori, vaccine, and vaccination and have conducted a systematic review of published clinical trials and animal model studies on vaccines against H. pylori and have tried to summarize why the vaccines are not effective or only partially effective.

EXPERT COMMENTARY

This is the perfect time to review vaccine development against H. pylori as, after several failed attempts, promising results were reported by Zeng et al. in 2015. Successful vaccine development requires knowledge of both the immune mechanisms active during natural infection by H. pylori, owing to the complicated host response against the pathogen, and the factors that allow the persistence of bacteria, such as genetic diversity of H. pylori. Moreover, various clinical trials are needed to prove vaccine efficacy.

Immunodominant epitope-specific Th1 but not Th17 responses mediate protection against Helicobacter pylori infection following UreB vaccination of BALB/c mice

Helicobacter pylori (H. pylori) infects more than half of the world’s population, causing chronic gastritis, peptic ulcers and gastric cancer. Urease B subunit (UreB), a conserved protein of H. pylori, is capable of inducing specific CD4⁺ T-cell responses and provides protection against this infection. Previous studies have confirmed the effectiveness of rUreB subunit vaccines in generating CD4⁺ T-cell-mediated protection, but less is known regarding the roles of different subtypes of T-cell immunity, such as Th1, Th2 and Th17, particularly the immunodominant epitopes inducing specific CD4⁺ T-cell responses, in vaccine-mediated protection. In this study, we demonstrated that the vaccination of BALB/c mice with rUreB resulted in significant antigen-specific Th1 and Th17 immune responses. Importantly, two novel Th epitopes, UreB_317–329 and UreB_409–421, which are recognized by a major population of CD4⁺ T cells, were identified in immunized mice. Our results demonstrated that two novel epitopes can simultaneously induce Th1 and Th17 immune responses; however, only the epitope vaccine-induced CD4⁺ T-cells secreting IFN-γ mediated the protection against H. pylori; cells secreting IL-17A did not. Taken together, our results suggest that two novel immunodominant epitopes can induce Th1 and Th17 immune responses, but only the induced Th1 lymphocytes mediate protection against H. pylori.

Mucosal immunization with a urease B DNA vaccine induces innate and cellular immune responses against Helicobacter pylori

BACKGROUND

Helicobacter pylori is recognized as a major risk factor for recurrent gastroduodenal inflammatory diseases and gastric adenocarcinoma. The high prevalence of H. pylori infection worldwide, the risks of side-effects from antibiotic therapy, and increasing resistance to antibiotics are the main primers for the development of improved H. pylori vaccines. The antigenic potential of its urease enzyme, a critical virulence factor required for colonization of the gastric mucosa, has been demonstrated in animal and human studies. An important but controversial issue in H. pylori vaccine studies is the type of immune response required to control infection. A new approach in H. pylori vaccinology is the administration of DNA vaccines, which has included heat-shock protein and catalase DNA vaccines.

MATERIALS AND METHODS

The H. pylori urease subunit B construct or vector alone was administered to mice via the intranasal route. Spleens and stomachs were examined on day 0 and weeks 3, 6, and 12 after immunization. Proliferation of spleen cells was assessed using the carboxyfluorescein diacetate succinimidyl ester-based flow cytometry assay and cytokine secretion from cultured spleen cells was detected by ELISA, after stimulation with the urease subunit B recombinant antigen. Total RNA was isolated from stomach and spleen tissue and the expression of beta-defensin and cytokine genes was monitored by reverse transcription followed by polymerase chain reaction (RT-PCR). Immunized mice were challenged with H. pylori and bacterial DNA quantified by TaqMan PCR.

RESULTS

The urease B subunit DNA vaccine increased INF-gamma secretion and splenocyte proliferation without inducing adverse effects in the spleen. Increase in gastric beta-defensin 1 and marked induction in local IL-10 : IFN-gamma ratio up to 12 weeks post-immunization suggest a potential role for local innate immune responses in protection at the site of infection. Although significant bacterial reduction in the stomachs of urease B subunit DNA-immunized mice was observed, intermediate reduction was also noted in the vector group. Increased defensin expression and adjuvant effects of the cytosine preceding guanosine motifs may contribute to this phenomenon. Our data confirm that cytosine preceding guanosine motifs, even without coadministration with antigen, can reduce extracellular bacterial load.

CONCLUSIONS

In this study, a DNA construct encoding the urease B subunit was assessed for its immune profile and its ability to reduce bacterial colonization in the murine stomach. Our studies suggest that local innate immune responses may play a greater role than previously supposed in limiting H. pylori colonization in the gastric mucosa.

Oral vaccination against Helicobacter pylori infection is not effective in mice with Fas ligand deficiency

The aim of this study was to delineate the role of the Fas pathway in vaccination against Helicobacter pylori. C57BL/6 and Fas ligand-deficient (gld) mice were divided into 3 groups: control, H. pylori infected, and orally vaccinated (H. pylori whole cell sonicate and cholera toxin adjuvant). Oral vaccination prevented H. pylori colonization in 78% of C57BL/6 mice compared to only 18% of gld mice. Vaccination did not alter the degree of apoptosis in either strain of mice. Vaccination led to significant increase in interleukin (IL)-5 and IL-10 in C57BL/6 but not gld mice. H. pylori infection increased interferon (IFN)-gamma levels in C57BL/6 but not in gld mice while vaccination had no effect on IFN-gamma levels in either strain. Oral vaccination is not effective in Fas ligand-deficient mice likely owing to lack of effective cytokine responses. This indicates that the Fas pathway plays a critical role in promoting an appropriate effector response following H. pylori vaccination.

Effectiveness of intragastric immunization with protein and oligodeoxynucleotides containing a CpG motif for inducing a gastrointestinal mucosal immune response in mice

PURPOSE

To investigate a new modality of mucosal vaccines, we evaluated the effectiveness of intragastric immunization for inducing a mucosal immune response in the gastrointestinal tract.

METHODS

Mice were immunized with beta-galactosidase (beta-gal) and synthesized oligodeoxynucleotides containing a CpG motif (CpG-DNA) by intragastric injection, and the immune response was compared with those induced by 3 other immunization forms: intranasal, oral, and intradermal.

RESULTS

Intragastric immunization with beta-gal and CpG-DNA induced significant anti-beta-gal fecal IgA production at 2 weeks; however, at 4 weeks the response was lacking. In contrast, intranasal immunization with beta-gal and CpG-DNA induced the highest anti-beta-gal fecal IgA production at 4 weeks.

CONCLUSION

Although intragastric immunization with protein and CpG-DNA induces a mucosal immune response in the gastrointestinal tract, intranasal immunization is the most effective to induce both mucosal and systemic immune responses. This finding may increase the possibility for developing vaccines against mucosal pathogens, especially Helicobacter pylori.

The Development of Therapeutic and Preventive Vaccines for Gastric Cancer and Helicobacter pylori

Gastric cancer is one of the most important worldwide public health problems. Convincing epidemiologic and etiologic associations have been made between the development of gastric cancer and infection with Helicobacter pylori. H. pylori not only has adapted to survive within the harsh environment of the stomach but also is able to modulate and avoid endogenous immune responses. The design and creation of efficacious vaccine strategies against H. pylori requires an understanding of the complex interactions that make up mucosal immunity. An effective vaccine strategy against H. pylori has the potential to affect significantly on population health worldwide.

Frequencies of the expression of main protein antigens from Helicobacter pylori isolates and production of specific serum antibodies in infected patients

AIM: To investigate the frequencies of the expression of main protein antigens of Helicobacter pylori (H pylori) isolates, such as UreB, VacA, CagA1, HpaA, NapA, FlaA and FlaB and the production of specific antibodies in sera from H pylori-infected patients, and to understand the correlations among the different clinical types of chronic gastritis and peptic ulcer and the infection and virulence of H pylori.

METHODS: H pylori strains in biopsy specimens from 157 patients with chronic gastritis and peptic ulcer were isolated and serum samples from the patients were also collected. The target recombinant proteins rUreB, rVacA, rCagA1, rHpaA, rNapA, rFlaA and rFlaB expressed by the prokaryotic expression systems constructed in our previous studies were collected through Ni-NTA affinity chromatography. Rabbit antisera against rUreB, rVacA, rCagA1, rHpaA, rNapA, rFlaA and rFlaB were prepared by using routine subcutaneous immunization. By using ultrasonic lysates of the isolates as coated antigens, and the self-prepared rabbit antisera as the first antibodies and commercial HRP-labeling sheep anti-rabbit IgG as the second antibody, expression frequencies of the seven antigens in the isolates were detected by ELISA. Another ELISA was established to detect antibodies against the seven antigens in sera of the patients by using the corresponding recombinant proteins as coated antigens, and the sera as the first antibody and HRP-labeling sheep anti-human IgG as the second antibody respectively. Correlations among the different clinical types of chronic gastritis and peptic ulcer and the infection and virulence of H pylori were statistically analysed.

RESULTS: In the 125 isolates of H pylori, the positive rates of UreB, VacA, CagA1, HpaA, NapA, FlaA and FlaB were 100%, 65.6%, 92.8%, 100%, 93.6%, 100% and 99.2% respectively. In the 125 serum samples from the H pylori-infected patients, the positive rates of antibodies against recombinant UreB, VacA, CagA1, HpaA, NapA, FlaA and FlaB were 100%, 42.4%, 89.6%, 81.6%, 93.6%, 98.4% and 92.8% respectively. H pylori strains were isolated from 79.6% (125/157) of the biopsy specimens, but no close correlations among the H pylori infection frequencies and different types of chronic gastritis and peptic ulcer could be found (P>0.05, χ² = 0.01-0.87). The VacA positive rate (82.40%) in the strains isolated from the specimens of patients with peptic ulcer and the anti-VacA positive rate (54.3%) in the sera from the patients were significantly higher than those (51.5%, 32.3%) from the patients with chronic gastritis (P<0.01, χ² = 13.19; P<0.05, χ² = 6.13). When analysis was performed in the different types of chronic gastritis, the VacA in the strains isolated from the specimems of patients with active gastritis showed a higher expression frequency (90.0%) than those from superficial (47.9%) and atrophic gastritis (30.0%) (P<0.05, χ² = 5.93; P<0.01,χ² = 7.50). While analysis was carried out in the strains isolated from the specimens with superficial (93.8%) and active gastritis (100%), NapA showed a higher expression frequency compared to that from atrophic gastritis (60.0%) (P<0.01, χ² = 8.88; P<0.05, χ² = 5.00).

CONCLUSION: The types of chronic gastritis and peptic ulcer and their severity are not associated with H pylori infection frequency but closely related to the infection frequency of different virulent H pylori strains. The optimal antigens for developing vaccine and diagnostic kit are UreB, FlaA, HpaA, FlaB, NapA and CagA1, but not VacA.

A plasmid immunization construct encoding urease B of Helicobacter pylori induces an antigen-specific antibody response and upregulates the expression of beta-defensins and IL-10 in the stomachs of immunized mice

The objectives of this study were to investigate the efficacy of a prototype DNA immunization construct encoding the urease B subunit enzyme of Helicobacter pylori (H. pylori) for inducing adaptive and innate immune responses in mice immunized via intramuscular or subcutaneous routes and to further explore the adjuvant effects of the CpG motifs in the vector. Antibody, cytokine, and beta-defensin profiles were assessed in the stomachs of immunized animals: experiments were terminated 3 months after immunization because there was a significant increase in the anti-H. pylori urease B antibody response at Week 6 in mice immunized with the urease B construct. A long lasting expression of IL-10 mRNA was noted. Furthermore, a marked and sustained increase in the mRNA expression of beta-defensins was also observed, particularly beta1. This study demonstrates that an H. pylori urease B DNA construct can induce innate as well as adaptive immune responses in the stomachs of immunized mice. Upregulation of beta-defensin gene expression followed immunization and we believe that this is the first report of a DNA vaccine inducing innate anti-microbial responses. Such complex molecular interactions that modulate both innate and adaptive immune responses may be of critical importance in the control of mucosal pathogens, such as H. pylori.

Construction of prokaryotic expression system of ltB-ureB fusion gene and identification of the recombinant protein immunity and adjuvanticity

AIM: To construct ltB-ureB fusion gene and its prokaryotic expression system and identify immunity and adjuvanticity of the expressed recombinant protein.

METHODS: The ureB gene from a clinical Helicobacter pylori (H pylori) strain Y06 and the ltB gene from Escherichia coli (E. coli) strain 44851 were linked into ltB-ureB fusion gene by PCR. The fusion gene sequence was analyzed after T-A cloning. A prokaryotic recombinant expression vector pET32a inserted with ltB-ureB fusion gene (pET32a-ltB-ureB) was constructed. Expression of the recombinant LTB-UreB protein (rLTB-UreB) in E. coli BL21DE3 induced by isopropylthio-β-D-galactoside (IPTG) at different concentrations was detected by SDS-PAGE. Western blot assays were used to examine the immunoreaction of rLTB-UreB by a commercial antibody against whole cell of H pylori and a self-prepared rabbit anti-rUreB serum, respectively, and determine the antigenicity of the recombinant protein on inducing specific antibody in rabbits. GM₁-ELISA was used to demonstrate the adjuvanticity of rLTB-UreB. Immunoreaction of rLTB-UreB to the UreB antibody positive sera from 125 gastric patients was determined by using ELISA.

RESULTS: In comparison with the corresponding sequences of original genes, the nucleotide sequence homologies of the cloned ltB-ureB fusion gene were 100%. IPTG with different dosages of 0.1-1.0 mmol/L could efficiently induce pET32a-ltB-ureB-E. coli BL21DE3 to express the rLTB-UreB. The output of the target recombinant protein expressed by pET32a-ureB-E. coli BL21DE3 was approximately 35% of the total bacterial proteins. rLTB-UreB mainly presented in the form of inclusion body. Western blotting results demonstrated that rLTB-UreB could combine with the commercial antibody against whole cell of H pylori and anti-rUreB serum as well as induce rabbit to produce specific antibody. The strong ability of rLTB-UreB binding bovine GM₁ indicated the existence of adjuvanticity of the recombinant protein. All the UreB antibody positive sera from the patients (125/125) were positive for rLTB-UreB.

CONCLUSION: A recombinant prokaryotic expression system with high expression efficiency of the target fusion gene ltB-ureB was successfully established. The expressed rLTB-UreB showed qualified immunogenicity, antigenicity and adjuvanticity. All the results mentioned above laid a firm foundation for further development of H pylori genetically engineered vaccine.

Construction of prokaryotic expression system of ureB gene from a clinical Helicobacter pylori strain and identification of the recombinant protein immunity

AIM: To clone ureB gene from a clinical isolate of Helicobacter pylori and construct a prokaryotic expression system of the gene and identify immunity of the expressed recombinant protein.

METHODS: ureB gene from a clinical H pylori strain Y06 was amplified by the high fidelity polymerase chain reaction technique. The target DNA fragment amplified from ureB gene was sequenced after T-A cloning. Prokaryotic recombinant expression vector pET32a inserted with ureB gene (pET32a-ureB) was constructed. The expression of recombinant UreB protein (rUreB) in E. coli BL21DE3 induced by isopropylthio-β-D-galactoside (IPTG) at different concentrations was examined by SDS-PAGE. Western blot using commercial antibodies against whole cell of H pylori and an immunodiffusion assay using a self-prepared rabbit anti-rUreB antibody were applied to determine immunity of the target recombinant protein. ELISA was used to detect the antibody against rUreB in sera of 125 H pylori infected patients and to examine rUreB expression in 109 H pylori isolates.

RESULTS: In comparison with the reported corresponding sequences, the nucleotide sequence homology of the cloned ureB gene was from 96.88-97.82% while the homology of its putative amino acid sequence was as high as 99.65-99.82%. The rUreB output expressed by pET32a-ureB-BL21DE3 was approximate 30% of the total bacterial proteins. rUreB specifically combined with the commercial antibodies against whole cell of H pylori and strongly induced rabbits to produce antibody with a 1:8 immunodiffusion titer after the animals were immunized with the recombinant protein. Serum samples from all H pylori infected patients were positive for UreB antibody and UreB expression were detectable in all tested H pylori isolates.

CONCLUSION: A prokaryotic expression system with high expression efficiency of H pylori ureB gene was successfully established. The expressed rUreB showed qualified immunoreactivity and antigenicity. High frequencies of UreB expression in different H pylori isolates and specific antibody against UreB in sera of H pylori infected patients indicate that UreB is an excellent antigen candidate for developing H pylori vaccine.

Construction of expression systems for flaA and flaB genes of Helicobacter pylori and determination of immunoreactivity and antigenicity of recombinant proteins

AIM: To clone flagellin genes A (flaA) and B (flaB) from a clinical strain of Helicobacter pylori (H pylori) and to construct prokaryotic expression systems of the genes and identify immunity of the fusion proteins.

METHODS: The flaA and flaB genes from a clinical H pylori isolate Y06 were amplified by high fidelity PCR. The nucleotide sequences of target DNA amplification fragments from the two genes were sequenced after T-A cloning. The recombinant expression vector pET32a inserted with flaA and flaB genes was constructed, respectively. The expressions of FlaA and FlaB fusion proteins in E. coli BL21DE3 induced by isopropylthio-β-D-galactoside (IPTG) at different concentrations were examined by SDS-PAGE. Western blot using commercial antibodies against whole cell of H pylori and immunodiffusion assay using self-prepared rabbit antiserum against FlaA (rFlaA) or FlaB (rFlaB) recombinant proteins were applied to the determination of the fusion proteins immunity. ELISA was used to detect the antibodies against rFlaA and rFlaB in sera of 125 H pylori infected patients and to examine rFlaA and rFlaB expression in 98 clinical isolates of H pylori, respectively.

RESULTS: In comparison with the reported corresponding sequences, the nucleotide sequence homologies of the cloned flaA and flaB genes were from 96.28%-97.13% and 96.31%-97.73%, and their putative amino acid sequence homologies were 99.61%-99.80% and 99.41%-100% for the two genes, respectively. The output of rFlaA and rFlaB expressed by pET32a-flaA-BL21DE3 and pET32a-flaB-BL21DE3 systems was as high as 40%-50% of the total bacterial proteins. Both rFlaA and rFlaB were able to combine with the commercial antibodies against whole cell of H pylori and to induce rabbits to produce specific antibodies with the same 1:2 immunodiffusion titers after the animals were immunized with the two recombinant proteins. Ninety-eight and zero point 4 and 92.80% of the serum samples from 125 patients infected with H pylori were positive for rFlaA and rFlaB antibodies, respectively. One hundred percent and 98.98% of the 98 tested isolates of H pylori were detectable for rFlaA and rFlaB epitopes, respectively.

CONCLUSION: Two prokaryotic expression systems with high efficiency of H pylori flaA and flaB genes were successfully established. The expressed rFlaA and rFlaB showed satisfactory immunoreactivity and antigenicity. High frequencies of FlaA and FlaB expression in different H pylori clinical strains and the general existence of specific antibodies against FlaA and FlaB in H pylori infected patients strongly indicate that FlaA and FlaB are excellent antigen candidates for developing H pylori vaccine.

Construction and characterization of bivalent vaccine candidate expressing HspA and Mr18000 OMP from Helicobacter pylori

AIM: To construct a recombinant vector which can express outer membrane protein (OMP) with M_r18000 and heat shock protein A (HspA) from Helicobacter pylori (H. pylori) in E. coli BL21, and to exploit the possibility for obtaining the vaccine conferring protection from H. pylori infection.

METHODS: The target gene of HspA was amplified from H. pylori chromosome by PCR, and then inserted into the prokaryotic expression vector pET32a (+) by restrictive endonuclease enzyme kpn I, BamH I simultaneously. The recombinant vector was used to sequence, and then together with pET32a (+)/Omp₁₈, digested by restrictive endonuclease enzyme Hind III and BamH I simultaneously. pET32a(+)/ HspA and Omp₁₈ were recovered from 1% agarose gel by gel kit, and ligated with T₄ ligase by BamH I digested viscidity end. The recombinant plasmid of pET32a(+)/HspA/Omp₁₈ was transformed and expressed in E. coli BL21 (DE3) under induction of IPTG. After purification, its antigenicity of the fusion protein was detected by Western blot.

RESULTS: Enzyme digestion analysis and sequencing showed that the target genes were inserted into the recombinant vector, composed of 891 base pairs, encoded objective polypeptides of 297 amino acid residues. Compared with GenBank reported by Tomb et al there were 1.3% and 1.4% differences in obtained H. pylori nucleotide sequence and amino acid residues, respectively. SDS-PAGE analysis showed that relative molecule mass (M_r) of the expressed product was M_r 51000, M_r of protein expressed by pET32a (+) was about M_r 20000, and soluble expression product accounted for 18.96% of total bacterial protein. After purification with Ni⁺²-NTA agarose resins, the purification of recombinant fusion protein was about 95%. Western blot showed that recombinant fusion protein could be recognized by the patients’ serum infected with H. pylori and anti-Omp₁₈ monoclone, suggesting that this protein had good antigenicity.

CONCLUSION: The gene coding for H. pylori M_r18000 OMP and HspA was cloned and expressed successfully. The results obtained lay the foundation for development of H. pylori protein vaccine and a quick diagnostic kit.

Construction of hpaA gene from a clinical isolate of Helicobacter pylori and identification of fusion protein

AIM: To clone hpaA gene from a clinical strain of Helicobacter pylori and to construct the expression vector of the gene and to identify immunity of the fusion protein.

METHODS: The hpaA gene from a clinical isolate Y06 of H. pylori was amplified by high fidelity PCR. The nucleotide sequence of the target DNA amplification fragment was sequenced after T-A cloning. The recombinant expression vector inserted with hpaA gene was constructed. The expression of HpaA fusion protein in E.coli BL21(DE3) induced by IPTG at different dosages was examined by SDS-PAGE. Western blot with commercial antibody against whole cell of H. pylori as well as immunodiffusion assay with self-prepared rabbit antiserum against HpaA fusion protein were applied to determine immunity of the fusion protein. ELISA was used to detect the antibody against HpaA in sera of 125 patients infected with H. pylori and to examine HpaA expression of 109 clinical isolates of H. pylori.

RESULTS: In comparison with the reported corresponding sequences, the homologies of nucleotide and putative amino acid sequences of the cloned hpaA gene were from 94.25%-97.32% and 95.38%-98.46%, respectively. The output of HpaA fusion protein in its expression system of pET32a-hpaA-BL21(DE3) was approximately 40% of the total bacterial proteins. HpaA fusion protein was able to combine with the commercial antibody against whole cell of H. pylori and to induce rabbit producing specific antiserum with 1:4 immunodiffusion titer after the animal was immunized with the fusion protein. 81.6% of the serum samples from 125 patients infected with H. pylori (102/125) were positive for HpaA antibody and all of the tested isolates of H. pylori (109/109) were detectable for HpaA.

CONCLUSION: A prokaryotic expression system with high efficiency of H. pylorihpaA gene was successfully established. The HpaA expressing fusion protein showed satisfactory immunoreactivity and antigenicity. High frequencies of HpaA expression in different H. pylori clinical strains and specific antibody production in H. pylori infected patients indicate that HpaA is an excellent and ideal antigen for developing H. pylori vaccine.

A study of recombinant protective H. pylori antigens

AIM: To construct a recombinant vector which can express M_r26000 outer membrane protein (OMP) from Helicobacter pylori (H. pylori), and to obtain the vaccine protecting against H. pylori infection and a diagnostic reagent kit quickly detecting H. pylori infection.

METHODS: The gene encoding the structural M_r26000 outer membrane protein of H. pylori was amplified from H. pylori chromosomal DNA by PCR, and inserted in the prokaryotic expression vector pET32a(+), which was transformed into the Top10 E. coli strain. Recombinant vector was selected, identified and transformed into BL-21(DE3) E. coli strain. The recombinant fusion proteins were expressed. The antigenicity of recombinant protein was studied by ELISA or immunoblotting and immunized Balb/c mice.

RESULTS: The gene of M_r26000 OMP was amplified to be 594 base pairs, 1.1% of the cloned genes was mutated and 1.51% of amino acid residues was changed, but there was homogeneity between them. The recombinant fusion protein encoded objective polypeptides of 198 amino acid residues, corresponding to calculated molecular masses of M_r26000. The level of soluble expression products was about 38.96% of the total cell protein. After purification by Ni-NTA agarose resin columniation, the purity of objective protein became about 90%. The ELISA results showed that recombinant fusion protein could be recognized by patient serum infected with H. pylori and rabbit serum immunized with the recombinant protein. Furthermore, Balb/c mice immunized with the recombinant protein were protected against H. pylori infection.

CONCLUSION: M_r26000 OMP may be a candidate vaccine preventing H. pylori infection.

Oxidised mannan-listeriolysin O conjugates induce Th1/Th2 cytokine responses after intranasal immunisation

Clearance of infectious organisms does not always require polarised Th1 or Th2 responses and it may be advantageous for both Th1 and Th2 responses to be elicited for effective protection against an invading pathogen. It was the aim of this study to investigate oxidised mannan as a possible Th1/Th2 adjuvant. Oxidised mannan was conjugated to two candidate antigens and delivered intranasally to mice. Immunisation with the oxidised conjugate resulted in significant antigen specific proliferative responses, IL-2, IFN-gamma and IL-4 production when compared to unconjugated controls.

Is there another chapter in the Helicobacter pylori/peptic ulcer disease story?

The role of Helicobacter pylori in the production of mucosal damage has largely been considered within a simple infection paradigm, because to date eradication has appeared to be a predictable outcome of antibiotic therapy. Changes in the epidemiology and management of peptic ulcer disease, however, require a more comprehensive framework to understand these shifting clinical patterns. The present review examines mucosal damage as an outcome of a complicated host-parasite relationship, with alterations in both parasite physiology and host defence mechanisms being keys to understanding disease patterns.