Evaluation of the anti-East Asian CagA-specific antibody for CagA phenotyping

Abstract

The determination of the cagA genotype is generally based on sequencing the variable 3' region of the cagA gene. In a previous study, we successfully generated an anti-East Asian CagA-specific antibody (anti-EAS Ab) immunoreactive only with the East Asian CagA and not with the Western CagA. In a small number of Japanese patients, anti-EAS Ab appeared to be a useful tool for phenotyping CagA immunohistochemically. The present study was conducted to validate the anti-EAS Ab immunohistochemistry method in a larger number of patients from Vietnam and Thailand. A total of 385 Vietnamese and Thais were recruited. Helicobacter pylori status was determined by a combination of three methods, including culture, histology, and immunohistochemistry with anti-H. pylori antibody. The sensitivity, specificity, and accuracy of the anti-EAS Ab immunohistochemistry method for the diagnosis of CagA phenotype were calculated based on the results of the cagA sequencing as the gold standard. The sensitivity, specificity, and accuracy of our immunohistochemistry method were 96.7%, 97.9%, and 97.1%, respectively. Moreover, anti-EAS Ab was not cross-reactive with noninfected gastric mucosa. In conclusion, immunohistochemistry with anti-EAS Ab appears to be a good method for determination of CagA phenotype.

FIG. 1.

Scheme of the study.

FIG. 2.

Lack of cagA expression due to deletion of its promoter region. In seven H. pylori strains, HC25, HC58, HC61, HC143, HC148, HN91, and HN146 (lanes 3 to 9, respectively), absence of the cagA promoter region was detected by PCR with CagAP-Set1 primers (A) and confirmed by dot blot analysis (B). These strains did not produce CagA protein, as revealed by Western blotting (C).

FIG. 3.

Diagnosis of cagA genotype by immunohistochemistry. Sections from gastric biopsy specimens VA49 (A and B) and VB84 (C and D) were subjected to immunohistochemistry with anti-H. pylori antibody (α-HpAb) (A and C) and anti-East Asian-specific antibody (α-EAS Ab) (B and D). Sample VA49, which was infected by East-Asian CagA-producing H. pylori, was stained with anti-EAS Ab (B), whereas VB84, infected with Western CagA-producing H. pylori, was not (D). The presence of H. pylori in both specimens was confirmed by positive immunoreactivity with anti-H. pylori Ab (A and C). Original magnification, ×100.