Helicobacter pylori Omp18 and its application in serologic screening of infection.

Helicobacter pylori (Hp) is a major risk factor for gastrointestinal disorders including gastric cancer. We evaluated host serum antibody responses toward outer membrane protein18 in comparison with Urease A and B subunits. omp18 and ureA-ureB gene fragments were PCR amplified, cloned, and expressed in E. coli expression system. The expressed proteins were visualized on SDS-PAGE and confirmed by immuno-blotting. Purified proteins were applied in western blotting assays in comparison with local and foreign ELISA kits. ROC curve analysis identified the optimum cut-off points for each protein. rOmp18 represented the highest rates of sensitivity (94%), specificity (89%), PPV (97.4%), NPV (77.4%), and accuracy (93.2%) in comparison with urease A and B subunits. These immunologic indices were in "substantial" agreement (Κ = 0.7) with the gold standard tests for Hp detection. This study recommends Hp conserved Omp18 as a reliable serologic marker for accurate detection of Hp infection particularly for application in population screening approaches.