Helicobacter pylori cagA and vacA cytotoxin genes in Changsha, China

Low frequency of cagA-positive Helicobacter pylori strains isolated from Iranian patients with MALT lymphoma

Helicobacter pylori is predominantly involved in the etiology of digestive diseases. The aim of our study is to determine the relationship of cagA frequency with less investigated gastroduodenal disorders such as MALT (mucosal associated lymphoid tissue) lymphoma and gastric cancer. One hundred-twenty eight H. pylori-positive patients including: gastritis (n = 74), gastric cancer (n = 26) and MALT lymphoma (n = 28) were entered in our study. Antral biopsy specimen transport, bacterial culture and cagA detection were performed based on standard protocols. In brief, biopsies from positive H. pylori patients were investigated for presence of cagA gene by polymerase chain reactions (PCR) method. Of 128 consecutive Iranian patients with gastroduodenal disorders examined in our study, we identified 84 (65.6%) cagA-positive strains. However, six patients were excluded because of negative culture for identification of H. pylori. Prevalence of cagA in each categorized groups are following: 63/74 (85.1%) of gastritis patients, 16/28 (57.1%) and 5/26 gastric cancer (19.2%) of MALT lymphoma, respectively. Current findings reveal that the presence of cagA is not a reliable marker for prediction of digestive disorders caused by H. pylori infection. All our patients with gastric cancer were diagnosed as adenocarcinoma. The low rate of cagA among gastric cancer and MALT lymphoma groups was not statistically significant, possibly due to the small number of patients enrolled in the study. We suggest that a study with a high number of patients is needed for making more definitive assessment of the correlation between cagA-positive H. pylori and gastric cancer and MALT lymphoma.

Distinctiveness of the cagA genotype in children and adults with peptic symptoms in South China

BACKGROUND

Helicobacter pylori infection is different between children and adults, not only in infection rate but also in virulence genotypes. However, the 3' region of CagA, important in stomach carcinogenesis, still remains unclear in children. The present study aims to compare the frequency of cagA and the distribution of its subtypes between children and adults in South China.

MATERIALS AND METHODS

One hundred and twenty-eight children and 99 adults with peptic symptoms were enrolled in our research. Histology, rapid urease test, and real-time polymerase chain reaction (PCR) assay were used to diagnose H. pylori infection. vacA s1 was detected by real-time PCR, and EPIYA motifs in the 3' region of CagA by conventional PCR and DNA sequencing.

RESULTS

H. pylori infection was diagnosed in 53 children and 62 adults. vacA s1 was identified in 90.6% and 91.9% of infected children and adults, respectively. Furthermore, cagA was identified in 73.6% and 82.3% of infected children and adults, respectively. No patient with multiple cagA subtypes was observed. A higher prevalence of more virulent cagA genotype was found in children compared to adults (p < .05). Thirty-eight of 39 (97.4%) cagA-positive children were found to have EPIYA-ABD and only one (2.6%) with EPIYA-ABC. In adults, four types of EPIYA motifs--ABC (29.4%), ABD (64.7%), ABAB (2%), and AAD (3.9%)--were identified, and the ABD type was found more commonly in severe diseases, such as atrophic gastritis (53.3%) and gastric cancer (71.4%).

CONCLUSION

cagA genotypes in children and in adults are different, and EPIYA-ABD may have potential clinical implication in the development of gastric cancer in South China.

Geographical conservation of short inserts in the signal and middle regions of the Helicobacter pylori vacuolating cytotoxin gene

Short nucleotide sequence inserts within the signal (s) and mid (m) regions of the vacuolating cytotoxin gene (vacA) of Helicobacter pylori provide the basis for defining the allelic forms widely used for strain typing and as markers for toxin functionality and severity of interactions with host gastric epithelial cells. Here 484 signal region and 411 mid-region sequences (new and from public databases) from 32 countries were analysed to determine the effect of geographical location on insert diversity, which is currently undefined. Short (27 bp) inserts of 52 mol% G+C from 201 sequences (98 %) of the s2 allelic family encoded a highly conserved nine amino acid sequence irrespective of geographical origin. The longer (75 bp) mid-region insert of 38 mol% G+C in 255 sequences of the m2 allelic family was more diverse and represented by 23 peptide variants, with one predominant sequence (MRI type 4) representing 62 % of inserts. Mid-region inserts were widespread throughout European/North American (Western) sequences in the dataset whereas a lower insert frequency was a geographical feature of East Asian sequences. Each insert was preceded by an associated conserved motif that provided a marker of the insertion sites within vacA, and facilitated identification of the Chinese m2b genotype. It is concluded that the observed sequence conservation supports the continued global use of vacA genotyping, and that inserts could have a functional significance in the mature protein, particularly the s2 form of the toxin, as the same combination of signal and mid-region insert type and preinsert motif was highly conserved.

Detection of H pylori antibody profile in serum by protein array

AIM: To detect multiple H pylori antibodies in serum samples of individuals who carryH pylori by protein array.

METHODS: Recombinant H pylori antigens, urease B subunit (UreB), vacuolating toxin A (VacA) and cytotoxin associated gene A protein (CagA), were prepared and immobilized in matrixes on nitrocellulose membrane by robotics to bind the specific immunoglobulin G (IgG) antibodies in serum. Staphylococcus protein A (SPA) labeled by colloid gold was used to integrate the immuno-complex and gave red color signal. The scanner based on charge-coupled device (CCD) could collect the image signal and convert it into digital signal.

RESULTS: When human IgG was printed on the membrane in increasing concentrations and incubated with immunogold, a linear dose response curve was obtained and the detection limit for IgG was about 0.025 ng. The cutoff values, which were defined as the mean grey level plus 3 times of standard deviation, were 27.183, 28.546 and 27.402, for anti-UreB IgG, anti-CagA IgG and anti-VacA IgG, respectively, as 400 human serum samples with negative H pylori antibodies were detected by the protein array. When 180 serum samples from patients in hospital were employed for detection of IgG against UreB, CagA and VacA, the sensitivity of the protein array was 93.4%, 95.4%, 96.0%, and the specificity was 94.8%, 94.4% and 97.5%, respectively, as compared with the results obtained by ELISA. The assay also showed high reproducibility, uniformity and stability, and the results were available within 30 min.

CONCLUSION: The protein array is a very practical method for rapid detection of multiple antibodies in serum samples. It is especially useful for large scale epidemiological investigation of the infection of H pylori.