CagA and cytotoxicity of Helicobacter pylori are not markers of peptic ulcer in Japanese patients

Frequencies of serum antibodies to Helicobacter pylori CagA and VacA in a Turkish population with various gastroduodenal diseases

Infection with Helicobacter pylori (H. pylori) strains secreting cytotoxin-associated gene A (CagA) and vacuolating cytotoxin A (VacA) proteins is associated with more severe gastroduodenal pathologies. However, this association varies among geographical regions and ethnic groups. We investigated the frequencies of antibodies to CagA and VacA proteins in 131 H. pylori-infected dyspeptic patients [40 duodenal ulcer (DU), 19 gastric ulcer (GU), 28 gastric cancer (GC), and 44 non-ulcer dyspepsia (NUD)] across 30 H. pylori-infected and endoscopically normal asymptomatic subjects (AS). Anti-CagA and anti-VacA antibodies were detected by Western blotting. The positivity rates of anti-CagA and anti-VacA antibodies were higher in patients with DU (92.5 and 75%), GU (89.5 and 84.2%) and GC (96.4 and 85.7%) than patients with NUD (70.5 and 50%) and AS (50 and 23.3%) (p < 0.05). CagA+ VacA+ phenotype was more frequent in patients with DU, GU and GC than patients with NUD and AS (75, 84.2, 85.7 vs. 47.7 and 20%, respectively) (p < 0.01). Our results showed that there is a significantly positive association between the presence of anti-CagA and anti-VacA antibodies and DU, GU and GC in our region.

Helicobacter pylori virulence factors in duodenal ulceration: A primary cause or a secondary infection causing chronicity

Reports from countries with a high prevalence of Helicobacter pylori (H pylori) infection do not show a proportionately high prevalence of duodenal ulceration, suggesting the possibility that H pylori cannot be a primary cause of duodenal ulceration. It has been mooted that this discrepancy might be explained by variations in the prevalence of virulence factors in different populations. The aim of this paper is to determine whether the published literature gives support to this possibility. The relevant literature was reviewed and analyzed separately for countries with a high and low prevalence of H pylori infection and virulence factors. Although virulent strains of H pylori were significantly more often present in patients with duodenal ulcer than without the disease in countries with a low prevalence of H pylori infection in the population, there was no difference in the prevalence of virulence factors between duodenal ulcer, non - ulcer dyspepsia or normal subjects in many countries, where the prevalence of both H pylori infection and of virulence factors was high. In these countries, the presence of virulence factors was not predictive the clinical outcome. To explain the association between virulence factors and duodenal ulcer in countries where H pylori prevalence is low, only two papers were found that give little support to the usual model proposed, namely that organisms with the virulence factors are more likely than those without them to initiate a duodenal ulcer. We offer an alternative hypothesis that suggests virulence factors are more likely to interfere with the healing of a previously produced ulcer. The presence of virulence factors only correlates with the prevalence of duodenal ulcer in countries where the prevalence of H pylori is low. There is very little evidence that virulence factors initiate duodenal ulceration, but they may be related to failure of the ulcer to heal.

Impact of Helicobacter pylori virulence factors and compounds on activation and maturation of human dendritic cells

Recently, we and others have shown that Helicobacter pylori induces dendritic cell (DC) activation and maturation. However, the impact of virulence factors on the interplay between DCs and H. pylori remains elusive. Therefore, we investigated the contribution of cag pathogenicity island (PAI) and VacA status on cytokine release and up-regulation of costimulatory molecules in H. pylori-treated DCs. In addition, to characterize the stimulatory capacity of H. pylori compounds in more detail, we studied the effect of formalin-inactivated and sonicated H. pylori, as well as secreted H. pylori molecules, on DCs. Incubation of DCs with viable or formalin-inactivated H. pylori induced comparable secretion of interleukin-6 (IL-6), IL-8, IL-10, IL-12, IL-1beta, and tumor necrosis factor (TNF). In contrast, IL-12 and IL-1beta release was significantly reduced in DCs treated with sonicated bacteria and secreted bacterial molecules. Treatment of sonicated H. pylori preparations with polymyxin B resulted in a significant reduction of IL-8 and IL-6 secretion, suggesting that H. pylori-derived lipopolysaccharide at least partially contributes to activation of immature DCs. In addition, the capacity of H. pylori-pulsed DCs to activate allogeneic T cells was not affected by cag PAI and VacA. Pretreatment of DC with cytochalasin D significantly inhibited secretion of IL-12, IL-1beta, and TNF, indicating that phagocytosis of H. pylori contributes to maximal activation of DCs. Taken together, our results suggest that DC activation and maturation, as well as DC-mediated T-cell activation, are independent of the cag PAI and VacA status of H. pylori.

A positive assay for identification of cagA negative strains of Helicobacter pylori

A new PCR protocol was developed for the positive identification of cagA negative Helicobacter pylori strains. Amplification of a portion of the genome across the insertion point of the cag pathogenicity island (the ES-"empty site") generated a 106-bp fragment, which produces a positive signal for cagA negative strains. Combined with the results of the cagA assay, the signals for ES allowed the complete characterization of the patients' cagA status. DNA sequencing analysis confirmed the identity of the ES fragment. The new protocol and cagA assay were applied to 22 DNA preparations isolated from stools from H. pylori infected adult patients and to 21 DNA preparations isolated from stools from H. pylori infected children. The same analysis was also performed on nine colonies of H. pylori derived from gastric biopsies of nine of the adult patients. The total number of cagA positive cases from adult patients was 14 or 63.6% (11 mono- and 3 mixed) and of the cagA negative cases (or ES positive) was 9 or 40.9% (6 mono- and 3 mixed). Of the 21 stool DNA samples from children, 6 (28.6%) were cagA positive, 12 (57.1%) were cagA negative and 3 (14.3%) were positive for cagA and for the ES simultaneously. The proportions of mixed cagA positive and cagA negative H. pylori infections were almost equal in adults and children (13.6% and 14.3%, respectively). No reaction products of the proper fragment sizes for cagA or the empty site (ES) were obtained from any of the stool DNA samples of 10 H. pylori uninfected subjects (100% specificity). This noninvasive assay discriminates consistently cagA negative cases from cagA positive strains and from amplification failures. It can be a useful tool for clinical and epidemiological studies of H. pylori infection.

Comparison of genotyping of Helicobacter pylori cagA and vacA virulence genes from gastric biopsies and stool specimens

BACKGROUND

We compared results of genotyping of Helicobacter pylori cagA and vacA virulence genes in DNA from gastric biopsies, both paraffin-embedded and frozen, and from stool samples, in order to evaluate the comparative sensitivity of the stool assay.

METHODS

Genomic DNA from paraffin-embedded biopsies, unfixed frozen biopsies, and stool samples of the same 20 patients was amplified for the cagA gene, an empty site (which provides a positive signal for cagA negative strains) and for the s and m alleles of the vacA gene. Composite genotypes were determined by combining data from analysis of all three materials.

RESULTS

Analysis of none of the materials taken singly showed all of the genotypes revealed by all three materials taken together, probably because of sampling error. Analysis of paraffin biopsies revealed 83.5%, that of frozen biopsies revealed 74.7% and that of stools revealed 75.9% of the genotypes. There was no significant difference in the percentage of the H. pylori genotypes identified from the three materials. Analysis of combinations of frozen biopsies and stools revealed 89.9% of the composite genotypes, and that of paraffin biopsies and stools revealed 96.2% of the composite genotypes. Evidence of multiple genotypes was found in 10 of 20 (50%) of the cases.

CONCLUSIONS

Any one of the investigated biological materials can be used for detection of cagA and vacA genes, but no single assay provided a complete genotype. The use of a combination of two materials may generate a more accurate representation of H. pylori genotypes in each individual.

Association of CagA and VacA presence with ulcer and non-ulcer dyspepsia in a Turkish population

AIM: The mostly known genotypic virulence features, of H. pylori are cytotoxin associated gene A (CagA) and Vacuolating cytotoxin gene A (VacA). We investigated the association of these major virulence factors with ulcer and non-ulcer dyspepsia in our region.

METHODS: One hundred and forty two dyspeptic patients were studied (average age 44.8 ± 15.9 years, range 15-87 years, 64 males and 78 females). Antral and corpus biopsies were taken for detecting and genotyping of H. pylori. 107 patients who were H. pylori positive by histological assessment were divided into three groups according to endoscopic findings: Duodenal ulcer (DU), gastric ulcer (GU) and non-ulcer dyspepsia (NUD). The polymerase chain reaction (PCR) was used to detect CagA and VacA genes of H. pylori using specific primers.

RESULTS: H. pylori was isolated from 75.4% (107/142) of the patients. Of the 107 patients, 66 (61.7%) were CagA-positive and 82 (76.6%) were VacA-positive. CagA gene was positively associated with DU and GU (P < 0.01, P < 0.02), but not with NUD (P > 0.05). Although VacA positivity in ulcer patients was higher than that in NUD group, the difference was not statistically significant (P > 0.05).

CONCLUSION: There is a significantly positive association between CagA genes and DU and GU. The presence of VacA is not a predictive marker for DU, GU, and NUD in our patients.

cagA and vacA in strains of Helicobacter pylori from ulcer and non-ulcerative dyspepsia patients

BACKGROUND

The cytotoxin associated gene A (cagA), and the vacuolating cytotoxin gene A (vacA) of Helicobacter pylori have been associated to phenotypic characteristics of virulence. The objectives of this study were to detect the presence of cagA and to characterize the allelic variants of vacA in 63 strains of H. pylori isolated from colonized individuals with different clinical outcomes.

METHODS

38 strains were isolated from patients with non-ulcerative dyspepsia (NUD) and 25 were isolated from colonized individuals with peptic ulcers. The genotypic characterization was carried out utilizing PCR methodology. The presence of the cagA gene was detected using two set of primers from the middle conservative region of the cagA, and primers for the signal and middle region were used for the genotyping of vacA.

RESULTS

The presence of cagA showed similar rates in strains from peptic ulcers (60%) and NUD patients (55%). Also similar was the prevalence of the allelic form s1 of vacA between the strains obtained from ulcers or NUD patients. However, the combination cagA+/vacA s1m1 was found more frequently among the H. pylori strains from peptic ulcer patients (52%) than among strains isolated from NUD patients (26%), this difference was statistically significant (p = 0.035).

CONCLUSIONS

The presence of either cagA or the allelic variant s1 vacA alone do not have a predictive value as as a risk markers of severe gastric pathologies in the Chilean population. However, being infected by a H. pylori strain with the genotype cagA+/vacA s1m1 may be associated to an increased risk of acquiring a peptic ulcer disease.

Prevalence of Helicobacter pylori in Sri Lanka as determined by PCR

Fifty-seven Sinhalese patients were investigated for the presence of Helicobacter pylori by PCR. A prevalence of 70.1%, with 47.5% positive for cagA, was demonstrated. The most common vacA allele was s1am1. There was no significant association between either the s1 allele or the cagA allele and severe gastroduodenal disease. There was an association between the s1 allele and the cagA locus.

Molecular epidemiology of Helicobacter pylori in England: prevalence of cag pathogenicity island markers and IS605 presence in relation to patient age and severity of gastric disease

The cagA gene is a key marker for the Helicobacter pylori cag pathogenicity island (PAI), which may vary in composition in different strains with insertion sequence mediated interruptions and deletions of genes. While presence of cagA has been associated with increased risk for peptic ulcer disease and gastric cancer, the precise link with virulence is controversial. We investigated H. pylori from dyspeptics in one location in England (mid-Essex) with reference to the prevalence and distribution by age cohort of different cag PAI forms to determine if presence of the insertion element IS605 had a modifying effect on the severity of associated disease. H. pylori isolated from gastric biopsies over a 4-year period were screened by specific PCR assays for the presence of cagA, cagD, cagE and virD4 genes in the cag PAI, and for the presence of IS605 in the PAI and elsewhere in the genome. Most (68%) of the 166 isolates of H. pylori contained a PAI based on detection of cagA whereas 29% had no detectable PAI using multiple loci. The cagA+ genotype frequencies were similar in the peptic ulcer and non-ulcer dyspepsia-gastritis groups (79% vs. 74%) whereas frequencies in the NUD-oesophagitis and normal mucosa groups were lower (58%) but not significantly different (P>0.41). Genomic IS605 inserts were present at an overall frequency of 32% and were widely distributed with respect to patient age and disease severity. The combined cagA+/IS- strain genotype was common but not significantly associated with PUD compared to endoscopically normal mucosa (P> or =0.807). We concluded that presence of the IS605 element, whether in cagA+ or cagA- strains of H. pylori, did not systematically modify the severity of associated disease in the study population.