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 Helicobact er pylori. Studies using purified proteins and an enzyme-linked immunosorbe nt assay (ELISA) method for serological detection of antibodies against Cag A reported considerable discordance between the results of the ELISA and mo lecular detection of the cagA gene, with a tendency for estimation of the p revalence of cagA-positive H. Pylori to be higher by ELISA than by colony h ybridization. It is not clear whether the discordance was either due to sim ultaneous infections with both cagA-positive and -negative strains or becau se of false-positive ELISA results. We correlated the presence of cagA-posi tive H. pylori by Polymerase chain reaction (PCR) with the presence of seru m antibodies against the CagA. protein from denatured H. pylori lysates. Ga stric 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 anti body-positive by Western blotting. The cagA gene is common in H. pylori iso lates from Korea regardless of the underlying disease. The presence of cagA is almost always associated with antibody to the CagA protein as determine d by Western blotting. Western blotting may be the preferred method for ser ological detection of infection with cagA-positive H. pylori.