Prevalence of CagA, VacA Antibodies in Symptomatic and Asymptomatic Children with Helicobacter pylori Infection

Background. Limited data are available on the prevalence of CagA and VacA Helicobacter pylori antibodies in children. The aim of this study was to investigate the antibody prevalence to the H. pylori virulence factors CagA and VacA in symptomatic and asymptomatic children with H. pylori infection and to correlate these antibodies with the severity of gastric inflammation or density of H. pylori organisms in the gastric mucosa.
Materials and Methods. Twenty-three symptomatic children and 132 asymptomatic children with positive H. pylori serology participated in this study. Anti– H. pylori IgG antibody and CagA or VacA H. pylori antibodies were measured by enzyme immunoassay (HM-CAP; sensitivity and specificity> 90%) and Western immunoblot (Helicoblot 2.0) methods, respectively. Gastric inflammation and H. pylori density were graded histologically using the revised Sydney criteria.
Results. The prevalence of CagA and VacA antibodies were 69% and 35% in symptomatic children and 54% and 52% in asymptomatic children, respectively. Multiple regression analysis showed a correlation between CagA antibody and the severity of gastritis but no correlation with other histological features, including the number of neutrophils or lymphoid follicles. Neither antibody correlated with the degree of bacterial density in the gastric mucosa.
Conclusion. CagA and VacA H. pylori antibodies are common in the pediatric population. The combined CagA/VacA antibodies correlated weakly with the degree of mucosal inflammation.     

Evaluation of a Western blot test,Helico blot 2.1, in the diagnosis of Helicobacter pylori infection in a pediatric population

Background. Noninvasive diagnostic tests are useful as screening tools for Helicobacter pylori infection in pediatric populations. The aim of this study was to evaluate performance of the immunoblot assay, Helico Blot 2.1, for the diagnosis of H. pylori infection in symptomatic children. Materials and Methods. Immunoblot assay was used for detection of IgG antibodies to specific H. pylori proteins and to a recombinant H. pylori antigen, CIM marker. The study was performed on sera collected from 134 symptomatic, untreated children (mean age, 9.1 ± 3.2 years; range, 1–14 years). H. pylori infection status was determined by culture, histology and rapid urease test. Results. Immunoblot assay yielded a positive result in 71 of the 72 infected patients (sensitivity 98.6%) and in eight of the 62 noninfected ones (specificity 87.1%). The predictive values for a positive and a negative result were 89.9% and 98.2%, respectively. The performance of the CIM band alone, as a marker for H. pylori infection status, was also evaluated. This band was present on the blot of 71 infected patients and on four of the 62 H. pylori‐negative patients. The sensitivity, specificity, PPV and NPV of the CIM antigen were 98.6%, 93.5%, 94.7% and 98.3%, respectively. Conclusions. The immunoblot assay Helico Blot 2.1 is a suitable noninvasive test for the serodiagnosis of H. pylori infection in children. The good level of performance demonstrated by the novel recombinant antigen CIM suggests it may be a useful contribution to the qualitative and quantitative performance of the Helico Blot 2.1 in pediatric populations.     

Performance of individual Helicobacter pylori antigens in the immunoblot-based detection of H. pylori infection

To develop a specific line blot (LB) for supporting ELISA-based serodiagnosis of Helicobacter pylori infection, individual native/recombinant H. pylori antigens were evaluated with respect to their reactivity with both serum IgG and IgA from 156 dyspeptic screening patients (67% H. pylori positive). Of 13 antigens, HP0175, p17, and p19 revealed highest positive likelihood ratios for H. pylori-specific IgG (> 5.0) and were selected as LB substrates, in addition to the established virulence markers VacA and CagA. For validation, the LB was compared to a commercial whole-cell-lysate-based ELISA by parallel (re-)analysis of 156 screening sera, 22 sera from diabetes mellitus patients and 15 sera from follow-up patients after H. pylori eradication. In screening patients, the combined use of IgG ELISA and LB revealed a sensitivity, specificity, and accuracy of 94%, 81%, and 90%, respectively, whereas IgG ELISA alone exhibited a low specificity of 75%. In diabetic and follow-up patients, IgA ELISA exhibited high accuracy of 89% and 93%, respectively, whereas IgG detection was unreliable (accuracy < 80%). In conclusion, using HP0175, p17, p19, CagA, and VacA as LB substrates significantly improves the specificity of anti-H. pylori IgG analysis, providing a reliable tool for (1) confirmation/refutation of ELISA-based screening results and (2) assessment of the CagA/VacA status.     

Aneurysm and Helicobacter pylori relationship: the seropositivity of CagA, VacA and other antigens of Helicobacter pylori in abdominal and ascending aortic aneurysms

Helicobacter pylori is thought to be related to atherosclerosis and aneurysm development. We aimed to detect virulance factors of H. pylori and examine the potential etiopathogenetic relationship between aortic aneurysm and H. pylori, 58 abdominal aortic aneurysm (AAA) and 38 ascending aortic aneurysm (AsAA) cases and 57 Healty control group (HCG) were included. We investigated H. pylori IgG by ELISA and virulance factors by Western-Blot (WB) method. No difference was found between AAA (67.24%), AsAA (73.68%) and HCG (57.89%) for H. pylori IgG (p > 0.05). A significant difference was found between AsAA (78.95%) and HCG (57.89%) for H.pylori IgG (p < 0.05) by ELISA and a significant difference was found only between AsAA (100%) and HCG (37.5%) for H. pylori IgG in the 45-55 age group by WB. A statistically significant difference was found between AAA and AsAA for VacA and CagA + VacA and CagA + VacA + UreA antigens and also a significant difference was found between AsAA and HCG for CagA + UreA antigens (p < 0.05). Finally, we suggest that H. pylori VacA has a more important role than CagA in the development of two aneurysms especially in ruptured AAA. New extended studies detecting H. pylori DNA are needed to detect the aetiopathogenesis between aneurysm types and H. pylori.     

CagA and VacA are immunoblot markers of past Helicobacter pylori infection in atrophic body gastritis

BACKGROUND AND AIM: Atrophic body gastritis (ABG) may be induced by H. pylori infection. It is difficult to diagnose H. pylori infection in this condition, since during progression of body atrophy the bacterium disappears. In 30% of patients with ABG no sign of H. pylori infection is detectable. We aimed to investigate whether patients with ABG, classified as H. pylori-negative by conventional methods (ELISA serology and Giemsa stain histology), have been previously exposed to the infection. METHODS: Case series consisted of 138 outpatients with ABG, of whom 31 are H. pylori negative (histology and ELISA serology), and 107 are H. pylori related (histology and ELISA serology positive: active infection, n = 29; only serology positive: past infection, n = 78). Thirty control subjects who were H. pylori negative at histology and ELISA serology were investigated. Immunoblotting of sera against H. pylori whole-cell protein lysate was performed. RESULTS: None of the control sera recognized CagA, VacA, heat-shock protein B, and urease B, yielding a specificity of 100%. All H. pylori-negative patients with ABG showed immunoblotting seroreactivity, including in each case either CagA or VacA. The concomitant seroreactivity against CagA and VacA was highly prevalent in the H. pylori-negative patients with ABG, comparable to those with active infection (77.4% vs. 86.2%) and with past infection (vs. 61.5%). CONCLUSIONS: Immunoblotting against CagA and VacA is able to prove past exposure to H. pylori infection in all patients with ABG defined as H. pylori-negative by conventional methods, suggesting a hidden role of H. pylori infection in gastric atrophy also in these patients.     

Helicobacter pylori Counteracts the Apoptotic Action of Its VacA Toxin by Injecting the CagA Protein into Gastric Epithelial Cells

Infection with Helicobacter pylori is responsible for gastritis and gastroduodenal ulcers but is also a high risk factor for the development of gastric adenocarcinoma and lymphoma. The most pathogenic H. pylori strains (i.e., the so-called type I strains) associate the CagA virulence protein with an active VacA cytotoxin but the rationale for this association is unknown. CagA, directly injected by the bacterium into colonized epithelium via a type IV secretion system, leads to cellular morphological, anti-apoptotic and proinflammatory effects responsible in the long-term (years or decades) for ulcer and cancer. VacA, via pinocytosis and intracellular trafficking, induces epithelial cell apoptosis and vacuolation. Using human gastric epithelial cells in culture transfected with cDNA encoding for either the wild-type 38 kDa C-terminal signaling domain of CagA or its non-tyrosine-phosphorylatable mutant form, we found that, depending on tyrosine-phosphorylation by host kinases, CagA inhibited VacA-induced apoptosis by two complementary mechanisms. Tyrosine-phosphorylated CagA prevented pinocytosed VacA to reach its target intracellular compartments. Unphosphorylated CagA triggered an anti-apoptotic activity blocking VacA-induced apoptosis at the mitochondrial level without affecting the intracellular trafficking of the toxin. Assaying the level of apoptosis of gastric epithelial cells infected with wild-type CagA⁺/VacA⁺ H. pylori or isogenic mutants lacking of either CagA or VacA, we confirmed the results obtained in cells transfected with the CagA C-ter constructions showing that CagA antagonizes VacA-induced apoptosis. VacA toxin plays a role during H. pylori stomach colonization. However, once bacteria have colonized the gastric niche, the apoptotic action of VacA might be detrimental for the survival of H. pylori adherent to the mucosa. CagA association with VacA is thus a novel, highly ingenious microbial strategy to locally protect its ecological niche against a bacterial virulence factor, with however detrimental consequences for the human host.     

Combined serum IgG response to Helicobacter pylori VacA and CagA predicts gastric cancer

Helicobacter pylori is a major factor for the development of gastric cancer. The aim of this study was to define serum antibody patterns associated with H. pylori infection in patients with gastric cancer using a Western blot technique. Serum samples collected from 115 patients with gastric cancer and 110 age- and gender-matched patients without gastrointestinal diseases were tested for IgG antibodies to H. pylori antigens (outer membrane proteins and whole cell preparations). No significant differences were found between patients with and without gastric cancer using outer membrane proteins (82% and 73%, P>0.05) or whole cell antigens (84% and 76%, P>0.05), respectively. The significant differences between patients with and without gastric cancer were associated with bands of 94 kDa (54% and 20%, P<0.001) and 30 kDa (65% and 44%, P<0.01). A combination of antibodies to 85 kDa (VacA) and 120 kDa (CagA) was significantly (P<0.01) more frequent in gastric cancer patients than in patients without gastric cancer. The detection of antibodies to 94- and 30-kDa bands, in association with the determination of serum antibodies to CagA+/VacA+, may have a prospective value in assessment of the risk of developing of gastric cancer.     

Serological responses of FldA and small-molecular-weight proteins of Helicobacter pylori: correlation with the presence of the gastric MALT tissue

PURPOSE: We tested whether the serological response to Flavodoxin-A (FldA) protein and anti-Helicobacter pylori immunoblots correlated to the degree of mucosaassociated lymphoid tissue (MALT) in the stomach. METHODS: Eighty H. pyloni-infected patients with different degrees of MALT in the stomach were investigated with serum sampling and endoscopy on enrolment, the 2nd and the 12th months after anti-H. pylori therapy. All sera were tested for the anti-FldA protein and anti-H. pylon immunoblots, including 19.5, 26.5, 30, 35, 89, and 116 KDa (CagA). Regression of follicular gastritis was assessed by histology. RESULTS: Patients with dense lymphoid follicles had higher prevalence rates of anti-FldA protein, 19.5, 26.5, and 30 KDa antibodies of H. pylori (p < .05). Histologic downgrade of MALT was observed in 25% (10/40) of patients in the 2nd month and in 60% (23/38) in the 12th month after H. pylori therapy. After H. pylori eradication, the patients with MALT and dense lymphoid follicles had significantly negative seroconversions of 19.5, 26.5, 30, and 35 KDa antibodies (p < .05), but not of CagA and FldA. CONCLUSION: Patients with gastric MALT and dense lymphoid follicles had different anti-H. pylori serological responses to those with scanty or an absence of lymphoid follicles. The negative seroconversion of the smaller-molecular-weight proteins, but not CagA and FldA, may correlate with the regression of MALT by H. pylori eradication.     

Helicobacter pylori Multiplex Serology

Background:  Helicobacter pylori infection is associated with severe gastrointestinal disease including cancer. It induces complex antibody responses that might vary depending on disease state but currently cannot be assessed adequately. The objective of this work was the development of a sensitive and specific H. pylori multiplex serology assay with high-throughput capability that allows simultaneous detection of antibodies to a protein array.
Methods:  Seventeen proteins of up to three H. pylori strains (26695, G27, 151), including CagA, VacA, UreA, Catalase, Omp, and GroEL, were recombinantly expressed as glutathione- S -transferase fusion proteins, affinity-purified, and used as antigens in a fluorescent bead-based antibody-binding assay. Reference sera (n   =   317) characterized by commercial assays (screening ELISA with Western blot confirmation) were used for validation.
Results:  H. pylori seropositivity by multiplex serology defined as reactivity with at least four proteins showed good agreement (kappa: 0.70) with commercial serologic assay classification, and a sensitivity of 89% and specificity of 82%. For individual antigens, agreement with Western blot was good for CagA (kappa: 0.77), moderate for UreA (kappa: 0.53), and weak for VacA (kappa: 0.12). Of the 13 proteins expressed from two strains, only VacA showed serologic strain differences. High antibody reactivity to CagA (Type I infection) was negatively associated with antibodies to GroEL, Cad, CagM, catalase, HcpC, NapA, and UreA, suggesting type-specific differences in protein expression patterns and/or immune response.
Conclusion:  With its high-throughput and simultaneous detection abilities, H. pylori multiplex serology appears suited as tool for large seroepidemiologic studies assessing H. pylori prevalence, antibody patterns, and associations with specific diseases.     

Fragmented CagA protein is highly immunoreactive in Japanese patients

Background: High‐molecular‐weight cell‐associated proteins (HM‐CAP) assay is the most popular serological immunoassay worldwide and has been developed from US isolates as the antigens. The accuracy is reduced when the sera are from adults and children in East Asia including Japan. To overcome the reduced accuracy, an enzyme immunoassay using Japanese strain–derived HM‐CAP (JHM‐CAP) was developed, in which the antigens were prepared by exactly the same procedure as HM‐CAP. The performance of JHM‐CAP was better than that of HM‐CAP in Japanese adults as well as in children. The higher sensitivity was because of the presence of 100‐kDa protein that was absent in the preparation of HM‐CAP antigen. Materials and Methods: Immunoblot analysis and peptide mass fingerprinting methods were used to identify the distinctive 100‐kDa protein present in JHM‐CAP antigens. The peptide sequence and identification were analyzed by Mascot Search on the database of Helicobacter pylori. The identified protein was confirmed by immunoblot with a specific antibody and inhibition assay by the sera. Results: The distinctive 100‐kDa protein was a fragment of CagA derived from Japanese clinical isolates, and the sera of Japanese patients had strongly reacted to the protein, probably to the exposed epitope on the fragmented CagA. The fragmentation of CagA had occurred in the process of antigen preparation in Japanese isolates, not in US isolates even under the same preparation. Conclusion: The distinctive 100‐kDa protein was a fragment of CagA protein of H. pylori derived from Japanese clinical isolates, and Japanese patients including children are likely to react strongly to the exposed epitopes on fragmented CagA.     

Is the Association Between Helicobacter pylori and Gastric Cancer Confined to CagA‐Positive Strains?

BACKGROUND: Infection with Helicobacter pylori is associated with an increased risk of gastric cancer. Several studies have indicated that the association differs with strain type. We aimed to find out if infection with strains lacking the virulence factor CagA is linked to gastric cancer risk. MATERIALS AND METHODS: In a hospital-based case-control study, we collected sera from 100 case patients with a newly diagnosed gastric adenocarcinoma and 96 control patients with diseases unrelated to H. pylori status. Antibodies to H. pylori were analyzed by enzyme-linked immunosorbent assay (ELISA), and antibodies to CagA were detected by immunoblot. Logistic regression was used to obtain odds ratios (ORs) as estimates of relative risk, adjusted for potential confounding. RESULTS: Among the case patients, 81% were ELISA positive and 86% had antibodies to CagA. The corresponding numbers among the controls were 58% and 55%, respectively. ELISA positivity was associated with an increased risk of gastric adenocarcinoma compared to ELISA negativity (OR for gastric cancer regardless of site 3.9, 95% CI 1.9-8.2). The OR was 7.4 (95% CI 3.3-16.6) for CagA-positive relative to CagA-negative subjects. Among ELISA-positive subjects the presence of CagA antibodies increased the risk 3.6 times (95% CI 1.2-11.1). ELISA-positive CagA-negative infections were associated with a fourfold increased risk (OR = 4.2, 95% CI 1.0-17.0) compared to no infection (ELISA-negative and CagA-negative). CONCLUSIONS: Although patients with antibodies to CagA have the greatest risk of developing gastric cancer, those with CagA-negative infections run a significantly greater risk than uninfected persons.     

Potential role of CagA in the inhibition of T cell reactivity in Helicobacter pylori infections

The pathogenicity of chronic gastroduodenal diseases is very often related to Helicobacter pylori infections. Most H. pylori strains carry the cagA gene encoding an immunodominant 120- to 128-kDa protein which is considered a virulence marker. The majority of CagA-positive H. pylori isolates also produce a 95-kDa protein cytotoxin (VacA) causing vacuolation and degradation of mammalian cells. In our previous study we have shown that live H. pylori bacteria and their sonicates inhibit PHA-driven proliferation of human T lymphocytes. The H. pylori CagA and VacA proteins were suspected of a paralyzing effect of H. pylori on T cell proliferation. In this report, by using isogenic H. pylori mutant strains defective in CagA and VacA proteins, we determined that CagA is responsible for the inhibition of PHA-induced proliferation of T cells.     

CagA and VacA: Virulence Factors of Helicobacter pylori in Thai patients with Gastroduodenal Diseases

Background. The aim of this study was to assess the seroprevalence of cytotoxin-associated gene A ( cag A) and vacuolating cytotoxin gene A ( vac A) of Helicobacter pylori in selected Thai populations with specific gastroduodenal diseases.
Materials and Methods. The immunoblot assay was used to detect serum antibodies against CagA and VacA obtained from the following patients: 87 cases of nonulcer dyspepsia (NUD), 61 cases of duodenal ulcer (DU), 49 cases of gastric ulcer (GU), and 10 cases of gastric cancer (GC).
Results. Serum antibodies to CagA were detected in 75.4% of all patients (70.1% of NUD, 78.7% of DU, 77.6% of GU, and 90% of GC). Although the prevalence of CagA seropositivity in GC patients was higher than in the other three groups, the difference was not statistically significant ( p > .05).
Conclusions. The high seroprevalence of the CagA-positive H. pylori strain in patients with peptic ulcer, GC, and NUD indicates that this strain is common in Thai patients with gastroduodenal diseases. Furthermore, phenotypic classification of H. pylori into type 1 (CagA-positive, VacA-positive) and type 2 (CagA-negative, VacA-negative) is not a useful marker for screening patients with severe forms of gastroduodenal diseases.     

13C-urea breath test to diagnose Helicobacter pylori infection in children aged up to 6 years

BACKGROUND: 13C-urea breath test (13C-UBT) is an accurate noninvasive tool for diagnosis of Helicobacter pylori infection. It is considered the best method for epidemiological studies, but there are few studies to evaluate the 13C-UBT in infants and toddlers. AIM: To evaluate the 13C-UBT performed with infrared spectroscopy in children aged up to 6 years. PATIENTS: Sixty-eight patients (6 months. to 5 years 11 months.) were evaluated prospectively and consecutively. METHODS: Helicobacter pylori infection was detected by positive culture, or rapid urease test and histological examination, both positive. 13C-UBT was performed with 50 mg of 13C-urea diluted in 100 ml of commercial orange juice. Two expired air samples were collected: before and 30 minutes after tracer ingestion. Cutoff of delta over baseline (DOB) was 4.0 per thousand and urea hydrolysis rate 10 microg/minute. RESULTS: Fifteen of 68 (22.1%) patients were H. pylori infected. Sensitivity was 93.3% (95% CI; 86.8%-99.7%) and specificity was 96.2% (95% CI; 93.6%-98.8%), and these values were equal for DOB and urea hydrolysis rate. Negative DOB values in noninfected patients ranged from -1.5 per thousand to 2.6 per thousand and positive DOB values ranged from 10.8 per thousand to 105.5 per thousand. There was no relationship between DOB values and age. Conclusion. 13C-UBT performed with infrared spectroscopy proved to be a reliable and accurate noninvasive diagnostic tool for H. pylori infection detection in children aged up to 6 years. Results far from cutoff value can clearly distinguish positive from negative 13C-UBT results in children up to 6 years old.     

Importance of EGF receptor, HER2/Neu and Erk1/2 kinase signalling for host cell elongation and scattering induced by the Helicobacter pylori CagA protein: antagonistic effects of the vacuolating cytotoxin VacA

Helicobacter pylori is the causative agent of gastric pathologies ranging from chronic gastritis to peptic ulcers and even cancer. Virulent strains carrying both the cag pathogenicity island ( cag PAI) and the vacuolating cytotoxin VacA are key players in disease development. The ca gPAI encodes a type IV secretion system (T4SS) which forms a pilus for injection of the CagA protein into gastric epithelial cells. Injected CagA undergoes tyrosine phosphorylation and induces actin-cytoskeletal rearrangements involved in host cell scattering and elongation. We show here that the CagA-induced responses can be inhibited in strains expressing highly active VacA. Further investigations revealed that VacA does not interfere with known activities of phosphorylated CagA such as inactivation of Src kinase and cortactin dephosphorylation. Instead, we demonstrate that VacA exhibits inactivating activities on the epidermal growth factor receptor EGFR and HER2/Neu, and subsequently Erk1/2 MAP kinase which are important for cell scattering and elongation. Inactivation of vacA gene, downregulation of the VacA receptor RPTP-α, addition of EGF or expression of constitutive-active MEK1 kinase restored the capability of H. pylori to induce the latter phenotypes. These data demonstrate that VacA can downregulate CagA's effects on epithelial cells, a novel molecular mechanism showing how H. pylori can avoid excessive cellular damage.     

Standardization of ELISA IgM and IgA for immunodiagnosis of human trichinosis

An ELISA test for trichinosis using as antigen a larvae soluble fraction from Trichinella spiralis was carried out for the detection of IgM and IgA specific antibodies in 45 serum samples from patients confirmed or suspected to have trichinosis by strong clinical and epidemiological evidences. All the patients had positive serology detected by precipitin test, bentonite floculation test, indirect hemagglutination test and ELISA IgG test. The cut-off value was determined using two criteria. Criterion A was determined in each plate, using three positive controls and two negative ones; the average of the negative controls and the weakest positive control, multiplied by a 1.2 factor was, considered the cut-off value. Criterion B was determined using the average plus three standard deviations from 64 apparently healthy persons serum samples. In both cases, three serum dilutions (1:10, 1:100 and 1:500) were used. The sensitivity of ELISA IgM was 100.0, 93.3 and 82.2% using serum dilutions of 1:10, 1:100 and 1:500 respectively (criterion A) and 100.0, 97.8 and 95.6% for the same dilutions (criterion B), whereas the values for ELISA IgA were: 100.0, 91.1 and 86.7% (criterion A) and 100.0, 100.0 and 91.1% (criterion B). In order to find out the specificity of ELISA IgM and ELISA IgA, additional 118 serum samples from individuals with other parasitoses, such as cysticercosis (18) hydatidosis (39), fascioliasis (12), toxocariasis (30), Chagas' disease (12) and individuals with non-specific eosinophilia (7), were also tested. ELISA IgM presented a specificity of 92.3, 93.4 and 97.3% (criterion A) and 96.2, 97.8 and 97.8% (criterion B) whereas the results for ELISA IgA were 97.8, 98.9 and 99.4% (criterion A) and 98.4% for the 1:10 and 1:100 dilutions and 100.0% for the 1:500 dilution (criterion B). The positive predictive values of ELISA IgM were 76.3, 77.8 and 88.1% (criterion A) and 86.5, 91.7 and 91.5% (criterion B) whereas the negative ones were 100.0, 98.3 and 95.7% (criterion A) and 100.0, 99.4 and 98.9% (criterion B). The positive predictive values of ELISA IgA were 91.8, 95.3 and 97.5% (criterion A) and 93.8, 93.8 and 100.0% (criterion B) whereas the negatives ones were: 100.0, 97.8 and 96.8% (criterion A) and 100.0, 100.0 and 97.8% (criterion B). The use of ELISA IgM and ELISA IgA in the immunodiagnosis of trichinosis is discussed.     

The Helicobacter pylori's protein VacA has direct effects on the regulation of cell cycle and apoptosis in gastric epithelial cells

In this study, we have evaluated the effects on cell cycle regulation of VacA alone and in combination with other two Helicobacter pylori proteins, cytotoxin-associated protein (CagA) and HspB, using the human gastric epithelial cells (AGS). Our results indicate that VacA alone was able to inhibit the G1 to S progression of the cell cycle. The VacA capacity of inhibiting cell progression from G1 to S phase was also observed when cells were co-transfected with CagA or HspB. Moreover, VacA over-expression caused apoptosis in AGS cells through activation of caspase 8 and even more of caspase 9, thus indicating an involvement of both the receptor-mediated and the mitochondrial pathways of apoptosis. Indeed, the two pathways probably can co-operate to execute cell death with a prevalence of the mitochondrial pathways. Our data taken together provide additional information to further enhance our understanding of the molecular mechanism by which H. pylori proteins alter the growth status of human gastric epithelial cells.     

Helicobacter pylori CagA containing ITAM-like sequences localized to lipid rafts negatively regulates VacA-induced signaling in vivo

Background. Helicobacter pylori CagA is injected into the host cell and tyrosine‐phosphorylated. We examined tyrosine‐phosphorylation sites of CagA, as well as the function of CagA proteins in vivo and in vitro. Methods. After proteolytic digestion of CagA with lysyl endopeptidase, CagA tyrosine‐phosphorylation sites were determined using quadropolar time‐of‐flight (Q‐TOF) mass spectrometry analysis. Specific anti‐pY CagA polyclonal and anti‐CagA monoclonal antibodies were used to examine gastric mucosal biopsy specimens from H. pylori infected patients. Results. Mass spectrometry identified five crucial tyrosine‐phosphorylation sites of CagA at Tyr893, Tyr912, Tyr965, Tyr999, and Tyr1033 within the five repeated EPIYA sequences of H. pylori (NCTC11637)‐infected AGS cells. CagA protein also had an immuno‐receptor tyrosine‐based activation motif (ITAM)‐like amino acid sequences in the 3′ region of the cagA, E PIY ATI x₂₇EIY ATI , which closely resembled the ITAM. CagA proteins: (i) were localized to the 1% TritonX‐100 resistant membrane fraction (lipid rafts); (ii) formed a cluster of phosphorylated CagA protein complexes; (iii) associated with tyrosine‐phosphorylated GIT1/Cat1 (G protein‐coupled receptor kinase‐interactor 1/Cool‐associated tyrosine‐phosphorylated 1), substrate molecules of receptor type protein‐tyrosine phosphatase (RPTPζ/β), which is the receptor of VacA; and (iv) were involved in a delay and negative regulation of VacA‐induced signal. Furthermore, immunohistochemical staining of gastric mucosal biopsy specimens provided strong evidence that tyrosine‐phosphorylated CagA is found together with CagA at the luminal surface of gastric foveola in vivo. Conclusion. These findings suggest an important role for CagA containing ITAM‐like sequences in the pathogenesis of H. pylori‐related disease.     

Interaction of Helicobacter pylori with host cells: function of secreted and translocated molecules

Secreted proteins are of general interest from the perspective of bacteria-host interaction. The gastric bacterial pathogen Helicobacter pylori uses a set of secreted and translocated proteins--including outer membrane adhesins, secreted extracellular enzymes and translocated effector proteins--to adapt to its extraordinary habitat, the gastric mucosa. Two major virulence factors of H. pylori are the vacuolating cytotoxin (VacA) and the cag type-IV secretion system and its translocated effector protein, cytotoxin-associated antigen A (CagA). VacA targets not only epithelial cells, but also cells of the immune system and induces immunosuppression. CagA has been shown to interact with a growing set of eucaryotic signaling molecules in phosphorylation-dependent and -independent ways.     

Presumptive mechanisms of peptic ulceration by Helicobacter pylori VacA involving mucoprotease and CagA.

Helicobacter pylori vacuolating toxin (VacA) appears to be unusually stable, not only against extreme pH conditions or high temperatures, but also against common organic solvents or detergents. Under acidic conditions, its activity was markedly increased in the manner of temperature-independent, suggesting a spontaneous activation. A similar finding was also observed under alkaline conditions, however, it should have an appropriate temperature. From these observations, the mechanisms of VacA activation were suggested to be so redundant that either the case of acidic or basic amino acid residues could be involved in the VacA activation. Separately, we also found that the VacA production by H. pylori was pH-dependent: Its production was increased at a low pH region with a broad range (1.0-5.0), and at a high pH region with a narrow range (8.0-9.0). Astonishingly, a highly immunogenic CagA did not appear to be expressed under the acidic conditions. Its expression, however, was shown to be enhanced when the surrounding pH of this bacterium was raised. In contrast, mucoproteolytic activity in the H. pylori membrane was found to be increased at acidic conditions. Considering these observations, together with the stomach and duodenal pH of humans, two presumptive mechanisms of H. pylori VacA-associated ulceration may be deduced; namely, an acid- and an alkali-dependent type, involving mucoprotease and CagA, respectively.