Characterizing antigenic determinants in Helicobacter pylori CagA capable of detecting serum antibodies in children

Helicobacter pylori can persistently colonize the mucosa of the human stomach, resulting in gastric disorders. Endoscopic biopsy for rapid urease test and histopathologic examination are considered as the most accurate diagnostic methods for H. pylori infection. Serological methods are recommended for children because of invasiveness of the diagnosis mentioned above. Here, the cytotoxin-associated gene A protein (Cag A), as an immunodominant antigen, was subdivided to determine which regions harbor antigenicity for humans. CagA was divided into 17 overlapping fragments of similar to 400 bp, which were used for the analysis of antigenic determinants. The partial proteins were subjected to immunoblot analysis using pooled serum samples from children with gastric symptoms. A partial recombinant CagA protein containing epitope regions (683-749 amino acids), which were identified in this study, was produced and used for the detection of anti-CagA antibodies and further investigated its serodiagnostic value for determination of H. pylori infection in children. The serum IgG reactivities from children with gastric symptoms were significantly three times more than that of serum samples from children with non-gastric symptoms (P < 0.005). Moreover, the serum IgG reactivities from children showing strong urease activity of gastric biopsies were significantly higher than those with moderate and weak urease activities (P < 0.05). Hence, the partial CagA is a candidate antigen for diagnosis of H. pylori infection.