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Helicobacter pylori anti-CagA antibodies: DISCUSSION Part 2

DISCUSSIONImmunoblotting is a more sensitive serological test than ELISA for the diagnosis of H pylori infection and the detection of specified antigens. With immunoblot testing, no significant age difference in the response to CagA antigen between patients older than 45 years and those younger than 45 years of age was found, indicating that the prevalence of CagA-positive strains is not restricted to older age and that subjects in different age groups mount a good antibody response to the CagA antigen.
An increase in the prevalence of anti-CagA antibodies has been reported in patients with peptic ulcer disease and those with gastric cancer. There appears to be major geographic differences in the prevalence of CagA-positive strains. In Australia, the prevalence of antibodies to CagA in patients with duodenal ulcer was higher than that in those with nonulcer dyspepsia and in asymptomatic people, while in China, no significant difference in the prevalence of CagA antibodies between asymptomatic and gastric cancer groups was found. In another study, host and environmental factors were found to be more important in the development of the disease. In the present study, the detection of such antibodies in the sera of symptomatic and asymptomatic subjects indicates that CagA-positive H pylori strains prevailed in both groups. These results appeared to be in agreement with those of previously published reports. Rocha et al indicated that immunoblotting using the Helico-Blot kit is useful for the diagnosis of H pylori infection in children and that the frequency of immunoreactive bands to CagA antigen is higher in children with duodenal ulcer than in children without the disease. However, Mitchell et al reported in an earlier study that antibody to CagA is not a marker for specific disease in children. More recently, Figueiredo et al compared the Helico-Blot kit with two other noncommercially developed enzyme immunoassays and concluded that the detection of anti-CagA antibodies is strongly dependent on the test used. The limitations reported by Figueiredo et al in their interpretation of the results were due to several factors that included observer visual scoring, low intensity of some signals and variation between different strip batches that prevent accurate alignment. These limitations were overcome in our study by the use of Gel Doc and the Quantity One software program for imaging and analysis.

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