Molecular Cloning of Immunodominant Antigen Epitopes of Helicobacter pylori for Development of a Specific ELISA to Diagnose H. pylori Infection

Helicobacter (Campylobacter) pylori has been implicated in the etiology of gastritis and peptic ulcer disease. H. pylori infection is normally diagnosed by microscopy and culture of biopsy samples. However, this is not only invasive but is time consuming and expensive. Various noninvasive serological techniques have been developed for diagnosing infection and ELISA is the most commonly used test. ELISAs that are based on H. pylori whole cells, sonicates or crude extracts have levels of sensitivity and specificity of 70%–90% [4]. A slight improvement has generally been reported by using acid cell extracts [7]. However, all these preparations contain antigens that cross-react with other bacterial species and cause false-positive reactions [5]. Adjusting the cut-off value only increases the number of false negatives. Second-generation ELISA systems have been developed which are based on high molecular weight conserved H. pylori specific purified antigens [4, 5]. They have high sensitivity and specificity and contain urease as the major antigenic component. High molecular weight fractionated antigens of H. pylori have also been isolated from SDS-PAGE gels [6] and these preparations may also be used for a H. pylori specific ELISA system. Molecular cloning of H. pylori immunodominant polypeptides can provide a useful, quick, high yield of H. pylori antigens that can be standardised and used for a specific diagnostic ELISA. We have previously reported the cloning of genes encoding 66 and 31 kDa immunodominant polypeptides of H. pylori in E.coli [3]. These antigens were demonstrated to be conserved, H. pylori-specific subunits of the H. pylori urease enzyme [2].