Serologic detection of Helicobacter pylori infection with cagA-positive strains in duodenal ulcer, gastric cancer, and asymptomatic gastritis.

CagA has been suggested as a marker for more virulent strains of Helicobacter pylori. Studies using purified proteins and an enzyme-linked immunosorbent assay (ELISA) method for serological detection of antibodies against CagA reported considerable discordance between the results of the ELISA and molecular detection of the cagA gene, with a tendency for estimation of the prevalence of cagA-positive H. Pylori to be higher by ELISA than by colony hybridization. It is not clear whether the discordance was either due to simultaneous infections with both cagA-positive and -negative strains or because of false-positive ELISA results. We correlated the presence of cagA-positive H. pylori by Polymerase chain reaction (PCR) with the presence of serum antibodies against the CagA protein from denatured H. pylori lysates. Gastric biopsies and sera were obtained from 75 patients from Korea; 25 each with gastric carcinoma, duodenal ulcer, and simple gastritis. Seventy-four of 75 isolates (98.6%) were cagA-positive by PCR and 70 sera were CagA antibody-positive by Western blotting. The cagA gene is common in H. pylori isolates from Korea regardless of the underlying disease. The presence of cagA is almost always associated with antibody to the CagA protein as determined by Western blotting. Western blotting may be the preferred method for serological detection of infection with cagA-positive H. pylori.