Proteomic characterization of Helicobacter pylori CagA antigen recognized by child serum antibodies and its epitope mapping by peptide array.

Serum antibodies against pathogenic bacteria play immunologically protective roles, and can be utilized as diagnostic markers of infection. This study focused on Japanese child serum antibodies against Helicobacter pylori, a chronically-infected gastric bacterium which causes gastric cancer in adults. Serological diagnosis for H. pylori infection is well established for adults, but it needs to be improved for children. Serum samples from 24 children, 22 H. pylori (Hp)-positive and 2 Hp-negative children, were used to catalogue antigenic proteins of a Japanese strain CPY2052 by two-dimensional electrophoresis followed by immunoblot and LC-MS/MS analysis. In total, 24 proteins were identified as candidate antigen proteins. Among these, the major virulence factor, cytotoxin-associated gene A protein (CagA) was the most reactive antigen recognized by all the Hp-positive sera even from children under the age of 3 years. The major antigenic part of CagA was identified in the middle region, and two peptides containing CagA epitopes were identified using a newly developed peptide/protein-combined array chip method, modified from our previous protein chip method. Each of the epitopes was found to contain amino acid residue(s) unique to East Asian CagA. Epitope analysis of CagA indicated importance of the regional CagA antigens for serodiagnosis of H. pylori infection in children.

Diagnostic accuracy of urine-based kits for detection of Helicobacter pylori antibody in children.

BACKGROUND: Rapid urine-HpAb is reported to be a reliable test of Helicobacter pylori infection in adults, but there are no data on the application of the test in children. The aim of this study was to evaluate the accuracy of a urine-based enzyme-linked immunosorbent assay (urine-HpELISA) and immunochromatography (rapid urine-HpAb) kit for anti-H. pylori immunoglobulin G antibody in children. We compared its sensitivity and specificity in reference to the (13) C-urea-breath test (UBT) and H. pylori stool antigen test (HpSA). METHODS: In total, 101 Japanese children without significant upper-abdominal symptoms were included (mean age, 7.1 years; range 2-15 years). Their sensitivity and specificity were evaluated in reference to the UBT and HpSA. RESULTS: Thirty-seven children were judged H. pylori-positive and 64 negative by the UBT and HpSA. No discrepancy in the results was observed between UBT and HpSA. Urine-HpELISA showed 91.9% sensitivity and 96.9% specificity with an accuracy of 95.0%. Rapid urine-HpAb showed 78.4% sensitivity and 100% specificity with an accuracy of 92.1%. Seven false negative results for rapid urine-HpAb were from children aged younger than 10 years, and their antibody titers of urine-HpELISA were lower than true positives. CONCLUSIONS: For the diagnosis of H. pylori infection in Japanese children, both tests are non-invasive, inexpensive, reliable and easy-to-perform methods giving satisfactory accuracy, although the sensitivity of the rapid urine-HpAb kit was inferior to that of the urine-HpELISA kit, especially in children aged younger than 10 years, showing relatively low titer of H. pylori antibody.