Assessment of Helicobacter pylori vacA and cagA Genotypes and Host Serological Response

Abstract

Helicobacter pylori strains can be distinguished by genotyping of virulence-associated genes, such as vacA and cagA. Because serological discrimination between strain types would reduce the need for endoscopy, 61 patients carrying H. pylori were studied by vacA and cagA genotyping of H. pylori in gastric biopsy specimens and by detection of specific serum antibodies. Serological responses to H. pylori were determined by Helicoblot (versions 2.0 and 2.1). Antibodies to CagA also were determined by a rapid anti-CagA assay (Pyloriset screen CagA) as well as by two noncommercially developed enzyme immunoassays, each using a recombinant CagA protein. Helicobacter pylori persistently colonizes the mucosa of the human stomach, causes chronic gastritis, and is an important risk factor for gastroduodenal diseases, such as peptic ulcers and gastric carcinoma (11). There is increasing evidence that distinct variants of H. pylori exist and that these may be associated with the pathogenicity of the bacterium (41); several virulence-associated genes have been identified (1,8).vacA encodes a vacuolating toxin that is released by H. pylori and injuries epithelial cells (9,21). vacA is present in all H. pylori strains, and includes two variable regions (1). The s region (encoding the signal peptide) is located at the 5Ј end of the gene and exists as an s1 or s2 allele. Within type s1, several subtypes (s1a, s1b, and s1c) can be distinguished (39). The m region (middle) occurs as an m1 or m2 allele. The mosaic combination of s-and m-region allelic types correlates with the production of the cytotoxin and is thereby associated with virulence of the bacterial strain (1).cagA (cytotoxin-associated gene) is considered a marker for the presence of the pathogenicity (cag) island of about 35 kbp (6). Carriage of cagA ϩ strains increases the risk for the development of atrophic gastritis and gastric cancer (4,19). Several studies have shown clinical relevance of specific antibodies to CagA using noncommercial assays (3,5,7,20,29,(33)(34)(35)44), whereas others failed to confirm these findings (14,17,18,23,27,45) H. pylori can be diagnosed by analysis of gastric biopsy specimens by urease tests, culture of the bacterium, histopathology, or detection of bacterial DNA by PCR. Noninvasive diagnostic methods include the urea breath test and serological assays measuring antibodies to H. pylori in the serum (15,22). The distinct vacA and cagA genotypes of H. pylori can best be identified by molecular methods, using cultured strains, or directly in gastric biopsy specimens, but this requires endoscopy. Therefore, serological typing methods analyzing specific antibodies to H. pylori if accurate, would be most suitable for routine clinical use. The present study assessed the relationship between the vacA and cagA genotypes of H. pylori and the presence of specific anti-Helicobacter antibodies, in particular, antibodies to CagA. MATERIALS AND METHODSPatients. Gastric (antral) biopsy specimens and serum samples were obtained from patients, undergoin...

Helicobacter pylori cagA and vacA genotypes in Cuban and Venezuelan populations

“…The mosaic combination of s and m region allelic types correlates with the production of the cytotoxin and is thereby associated with the virulence of the strain; the fact that the majority of the strains found in Cuban and Venezuelan patients are s1/m1, the most virulent type, is of importance to the regional health systems of both countries. These results are in accordance with several other studies (De Gusmão et al 2000, Figueiredo et al 2001, Chen et al 2005, Martins et al 2005, Garcia et al 2006.…”

Immunoblotting for the serodiagnosis of Helicobacter pylori infection in Brazilian patients with and without gastric carcinoma

“…In addition, as the antibodies react with defined antigens, the test allows the simultaneous detection of bacterium virulence factors. However, as there is a high degree of genetic heterogeneity among H. pylori strains and, consequently, in the proteins that are surface-exposed or secreted (Go et al 1996, Herbrink & van Doorn 2000, the assay must be validated for the population being studied (Mitchell et al 1996, Aucher et al 1998, Yamaoka et al 1998, Figueiredo et al 2001.…”

“…Commercial serological tests for H. pylori diagnosis have different performances in different populations, in part because of the variations in geographical distribution of the strains and in the antigenic preparations of the assays (Aucher et al 1998, Yamaoka et al 1998, Leung et al 2001, Figueiredo et al 2001. Thus, validating serological assays for each population in order to achieve more reliable results is recommended.…”

“…The presence of antibodies against H. pylori antigens can be evaluated by immunoblotting (Mitchell et al 1996, Aucher et al 1998, Yamaoka et al 1998, Figueiredo et al 2001, Park et al 2002. Although expensive and time-consuming, the test seems to be more sensitive than ELISA, especially when the levels of antibodies are low.…”

“…This is probably due to the fact that the individual bacterial proteins are better exposed, allowing antibodies to bind more easily (Nilsson et al 1997). The immunoblotting also allows the detection of antibodies to H. pylori virulence factors such as CagA and VacA (Yamaoka et al 1998, Figueiredo et al 2001, Park et al 2002.…”