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.     

Helicobacter pylori antibodies and gastric cancer: a gender-related difference

Helicobacter pylori has been proposed as a causative agent of gastric cancer. The aim of this study was to define serum antibodies response against different H. pylori antigens in patients with gastric cancer. Serum samples were collected from 115 Lithuanian patients with non-cardia gastric cancer and 110 age- and sex-matched controls without cancer. Heat-stable, low-molecular-mass, and outer membrane proteins were used as antigens to analyze serum IgG antibody response against H. pylori by enzyme-linked immunosorbent assay. Seroprevalence of H. pylori using low-molecular-mass antigen was significantly higher in gastric cancer patients, compared to controls (77% versus 57%, p<0.05). Significant differences in the prevalence of H. pylori infection between gastric cancer patients and controls were found in females using all three studied antigens: heat-stable (98% versus 84%, p<0.05), low-molecular-mass (88% versus 48%, p<0.05) and outer membrane proteins (78% versus 57%, p<0.05). In males, no significant differences were revealed between gastric cancer patients and controls. There may be other cofactors in addition to H. pylori that are important for the development of gastric cancer. H. pylori seems, however, to be a more important for development of gastric cancer in females than in males or males may have more confounding risk factors for gastric cancer than females.     

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.     

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.     

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.     

The accuracy of serologic diagnosis of Helicobacter pylori infection in school-aged children of mixed ethnicity

The present study evaluated two non-invasive diagnostic methods for H. pylori infection in children, i.e. an in-house ELISA using sonicated Campylobacter jejuni antigen for absorption of cross-reacting antibodies and an immunoblot kit (Helico Blot 2.0, Genelabs, Singapore). 13C -Urea breath test (13C-UBT) was used as reference METHOD: Sera and questionnaires were collected from 695/858 (81%) Swedish school children with mixed ethnic backgrounds within a cross-sectional, community-based study. Of 133 children with an ELISA OD value of > or = 0.1, all were screened with immunoblot and 107 made a 13C-UBT. The negative controls were 34/37 children from three school classes with an ELISA OD value of < 0.1 and volunteering for a 13C-UBT. An adjusted cut-off level for the ELISA of OD value 0.22 resulted in a sensitivity of 97.8%, a specificity of 95.8% and a concordance index of 97.2%. The Helico Blot 2.0 had a sensitivity of 97.8%, a specificity of 93.8% and a concordance index of 96.5%. The best concordance was seen for the 26.5 kDa (98.6%), 30 kDa (95.7%) and 19.5 kDa (91.5%) antigens. The corresponding concordance index for CagA was 78%, for VacA 73.8% and for the 35kDa antigen 68.8%. A significant difference in the distribution of the 19.5 and 26.5 kDa bands but not of CagA/VacA was noted by ethnic background. With an adjusted cut-off level for the enzyme-linked immunosorbent assay (ELISA), both non-invasive methods were found to have an adequate performance in a pediatric population. The differences in antibody response patterns by ethnic background represent a caveat in the interpretation of serological studies.     

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.     

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.     

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.     

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.     

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.     

Pathogenesis of Helicobacter pylori Infection

The clinical outcome of Helicobacter pylori infection is determined by a complex scenario of interactions between the bacterium and the host. The main bacterial factors associated with colonization and pathogenicity comprise outer membrane proteins including BabA, SabA, OipA, AlpA/B, as well as the virulence factors CagA in the cag pathogenicity island ( cag PAI) and the vacuolating cytotoxin VacA. The multitude of these proteins and allelic variation makes it extremely difficult to test the contribution of each individual factor. Much effort has been put into identifying the mechanism associated with H. pylori -associated carcinogenesis. Interaction between bacterial factors such as CagA and host signal transduction pathways seems to be critical for mediating the induction of membrane dynamics, actin-cytoskeletal rearrangements and the disruption of cell-to-cell junctions as well as proliferative, pro-inflammatory and antiapoptotic nuclear responses. An animal model using the Mongolian gerbil is a useful system to study the gastric pathology of H. pylori infection.     

不同部位、分化和起源胃癌中H.pylori、CagA基因的探讨

目的通过检测不同部位和不同组织类型中胃癌组织中幽门螺杆菌(H.pylori)和细胞毒素相关基因(CagA基因),探讨H.pylori、CagA基因与胃癌的关系,以及H.pylori、CagA基因导致胃癌的可能机制。方法应用快速尿素酶试验和组织切片革兰染色及血清H.pylori CagA抗体检测胃癌患者H.pylori,应用PCR检测胃癌组织中H.pylori CagA基因。结果胃癌组织中随活检部位不同,H.pylori检出率也不同,以胃窦部检出率最高为76.9%,与胃体大弯侧、胃角和贲门相比差异均有非常显著性(P0.005),胃体大弯侧、胃角与贲门相比差异均有非常显著性(P0.005),胃底与贲门相比差异无显著性(P0.05)。胃窦部癌的CagA检出率(85.6%)最高,与其他部位相比差异均有非常显著性(P0.005),胃角胃癌CagA检出率显著高于胃体大弯侧和贲门胃癌(P0.005)。高分化胃癌H.pylori检出率为73.1%,低分化胃癌H.pylori检出率为44.1%,二者相比差异均有非常显著性(P0.01)。肠型胃癌H.pylori检出率为76.7%,弥漫型胃癌H.pylori检出率为33.3%,二者相比差异有显著性(P0.05),高分化胃癌CagA检出率为26.3%,低分化胃癌CagA检出率为80.0%,二者相比差异均有非常显著性(P0.01)。肠型胃癌CagA检出率为80.4%,弥漫型胃癌CagA检出率为57.1%,二者相比差异无显著性(P0.05)。结论不同部位和不同组织类型中胃癌组织中H.pylori和CagA基因的表达存在一定差异性,对探讨胃癌的发生及胃癌的防治有一定的指导意义。     

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.     

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.     

External membrane vesicles from Helicobacter pylori induce apoptosis in gastric epithelial cells

The Helicobacter pylori infection of gastric mucosa is one of the most common infectious diseases and is associated with a variety of clinical outcomes, including peptic ulcer disease and gastric cancer. Helicobacter pylori-induced damage to gastric mucosal cells is controlled by bacterial virulence factors, which include VacA and CagA. Outer membrane vesicles are constantly shed by the bacteria and can provide an additional mechanism for pathogenicity by releasing non-secretable factors which can then interact with epithelial cells. The present report shows that external membrane vesicles are able to induce apoptosis not mediated by mitochondrial pathway in gastric (AGS) epithelial cells, as demonstrated by the lack of cytochrome c release with an activation of caspase 8 and 3. Apoptosis induced by these vesicles does not require a classic VacA+ phenotype, as a negative strain with a truncated and therefore non-secretable form of this protein can also induce cell death. These results should be taken into account in future studies of H. pylori pathogenicity in strains apparently VacA-.     

Lewis epitopes on outer membrane vesicles of relevance to Helicobacter pylori pathogenesis

BACKGROUND: Helicobacter pylori extrudes protein- and lipopolysaccharide-enriched outer membrane vesicles from its cell surface which have been postulated to act to deliver virulence factors to the host. Lewis antigen expression by lipopolysaccharide of H. pylori cells has been implicated in a number of pathogenic roles. The aim of this study was to further characterize the expression of lipopolysaccharide on the surface of these outer membrane vesicles and, in particular, expression of Lewis antigens and their association with antibody production in the host. MATERIALS AND METHODS: H. pylori strains were examined for outer membrane vesicle production using transmission electron microscopy and Lewis antigen expression probed using immunoelectron microscopy. Sera from patients were analyzed for cross-reacting anti-Lewis antibodies and, subsequently, absorbed using outer membrane vesicle preparations to remove the cross-reacting antibodies. RESULTS: The formation of outer membrane vesicles by H. pylori was observed in both in vitro and in vivo samples. Furthermore, vesicles were produced following culture in either liquid or solid medium by all strains examined. Moreover, we observed the presence of Lewis epitopes on outer membrane vesicles using immunoelectron microscopy and immunoblotting. Circulating anti-Lewis antibodies were found in the sera of gastric cancer patients but not in the sera of H. pylori-negative control subjects. Absorption of patient sera with outer membrane vesicles decreased the levels of anti-Lewis autoantibodies. CONCLUSIONS: Our results demonstrate the ability of H. pylori to generate outer membrane vesicles bearing serologically recognizable Lewis antigens on lipopolysaccharide molecules which may contribute to the chronic immune stimulation of the host. The ability of these vesicles to absorb anti-Lewis autoantibodies indicates that they may, in part, play a role in putative autoimmune aspects of H. pylori pathogenesis.     

The role of CagA status in gastric and extragastric complications of Helicobacter pylori.

Two major markers of virulence have been described in H. pylori. The first is a secreted protein (VacA) that is toxic to human cells in tissue culture. This cytotoxin causes vacuolation of epithelial cells in vitro and induces epithelial cell damage in mice. The second is a 40-Kb pathogenicity island for which the gene cagA (cytotoxin-associated gene A) is a marker. Approximately 60% of H. pylori isolates in Western countries are cagA+. The protein encoded by cagA+ has a molecular weight of 120-140 kDa and exhibits sequence heterogeneity among strains isolated from Western and Eastern countries. Although no specific function has been identified for CagA, there is increasing evidence that cagA+ strains are associated with increased intensity of gastric inflammation and increased mucosal concentration of particular cytokines including interleukin 8. Inactivation of picB (Hp 0544) or any of several other genes in the cag island ablates the enhanced IL-8 secretion of human gastric epithelial cells in tissue culture. Furthermore, persons colonized with cagA+ strains have an increased risk of developing more severe gastric diseases such as peptic ulcer and distal (non-cardia) gastric cancer than those harboring cagA- strains. We investigated the role of cagA status in both gastroduodenal and extragastroduodenal disease with H. pylori. Among the diseases limited to the antrum and body of the stomach and the duodenum, we demonstrated a correlation between CagA seropositivity and peptic ulcer disease. We also showed correlation between distal gastric cancer rated and CagA prevalence in populations in both developed and developing countries. In addition, we found that for several Asian populations, the relationship between CagA seropositivity and gastroduodenal diseases was complex. For extragastroduodenal diseases, our results confirmed previous reports that demonstrated that CagA status did not play a role in diseases such as rheumatoid arthritis and hyperemesis gravidarum. However, we found a clear negative association between the presence of a positive response to CagA and esophageal diseases. Therefore, CagA seropositivity (and thus gastric carriage) is associated with increased risks of certain diseases (involving the lower stomach and duodenum) and decreased risks of GERD and its sequelae. This apparent paradox can best be explained by differences in the interaction of cagA+ and cagA- strains with their hosts.     

Sequence Analysis of East Asian cagA of Helicobacter pylori Isolated from Asymptomatic Healthy Japanese and Thai Individuals

CagA, especially East Asian type, is one of the most important virulence factors of Helicobacter pylori, which is believed to contribute to the gastric cancer development. There is extreme sequence heterogeneity on 3' region of cagA gene, demonstrated by the sequence analysis of cagA of H. pylori strains isolated from gastric disease patients. However, whether such heterogeneity of the cagA gene sequence is related to the pathogenicity of H. pylori in the gastric cancer development is not certain. Therefore, in this study, the 3' region of cagA sequences isolated from asymptomatic healthy individuals in Japan and Thailand, which show high and low gastric cancer prevalence, respectively, were analyzed and compared with those from patients with gastric cancer. The CagA sequences analysis in 21 and 12 H. pylori DNA samples obtained from Japanese and Thai individuals, respectively, by the molecular phylogenetic method showed that the sequences were more conserved in the Thai individuals (concordance rates among Thai sequences, 93.9-100%) than in the Japanese individuals (concordance rates among Japanese sequences, 82.8-100%) as shown by unrooted neighbor-joining (N-J) consensus trees constructed with the sequence between Asn869 and Ala967 in CagA. CagA sequences in gastric cancer patients were obtained from published data; analysis of these sequences revealed that CagA sequences from almost all Thai individuals were concentrated in one branch. In contrast, CagA sequences from Japanese individuals were uniformly distributed throughout the N-J consensus tree. These results suggest that the difference in the CagA sequences between asymptomatic healthy Japanese and Thai individuals may be linked to the incidence of gastric cancer in Japan and Thailand.