Clinical relevance of CagA-specific antibodies related to CagA status of Helicobacter pylori isolates using immunofluorescence test and PCR

Background: The cagA (cytotoxin-associated gene A) protein is found in abou t 50% of Helicobacter pylon strains; its clinical relevance in gastroduoden al disease is uncertain. Patients and Methods: The frequency of IgG antibodies to cagA was studied b y using a commercial Western blot assay in sera of 189 patients with endosc opically and histologically confirmed gastroduodenal disease. In addition, 38 H. pylori strains isolated from biopsies were analyzed by immunofluoresc ence test (IFT) and PCR for detection of cagA protein and cagA gene sequenc es, respectively. Results: 54.3-60.0% of all patients with gastrointestinal diseases (chronic gastritis, gastric or duodenal ulcer and chronic duodenitis) and 28.6% wit h a normal mucosa were found to be positive for anti-cagA IgG antibodies. T here was no significant difference in anti-cagA IgG seroprevalence between the different clinical entities. CagA-positive (cagA(+)) H. pylori strains were detected in 44.7% and 50% of the 38 isolates by PCR and IFT, respectiv ely. 22 of 23 patients infected with cagA+ strains had anti-cagA antibodies . Using PCR as a gold standard, the sensitivity and specificity of the cagA IgG Western blot were 100.0% and 35.0%, respectively; the sensitivity and specificity of the cagA IFT were 76.5% and 71.4%, respectively. The inciden ce of the cagA+ H. pylori strains detected either by PCR or IFT was signifi cantly higher (p < 0.05 and p < 0.01, respectively) in patients with chroni c duodenitis, gastric or duodenal ulcer compared to patients with chronic g astritis (66.7%, 80% and 30.4%, respectively). Conclusion: In this study the cagA-specific serological status in H. pylori infections as diagnosed by IgG Western blot was of no predictive value for severity of disease. In contrast, the cagA status of H. pylori isolates, d iagnosed by IFT or PCR, was a predictive marker for severe disease and, the refore, also of clinical relevance in the assessment of the virulence of th e infecting strain.