CELL-SURFACE PROTEINS OF HELICOBACTER-PYLORI AS ANTIGENS IN AN ELISA AND A COMPARISON WITH 3 COMMERCIAL ELISA

Cell surface proteins of Helicobacter pylori were solubilized by extraction with acidic glycine buffer, N-octyl-glucoside, lithium chloride, and distilled water, and by sonication. The preparations were evaluated as antigens in ELISA to detect serum IgG responses in patients and healthy subjects. SDS-PAGE analyses of the preparations from a type strain (NCTC 11637) and of acidic glycine extracts of 4 clinical isolates showed multiple protein bands. The sera were classified as HP+ve and HP-ve by culture of biopsy and immunoblotting. Sera were considered positive for H. pylori if they detected the specific 120kD antigen or 4-5 other bands. 49 sera were HP+ve; the 51 HP-ve sera did not react in immunoblotting. 35/44 sera (80%) that reacted with the 120kD antigen demonstrated high titers in ELISA with all antigen preparations, and the remaining 9(20%) sera gave discordant results. 4/5 HP+ve sera that did not react with the 120kD antigen, demonstrated high ELISA titers with all 5 antigen preparations. Glycine extracts of 3 isolates did not exhibit the 120kD protein, but were equally sensitive in ELISA. The role of 120kD antigen in our ELISA was not clear. Immunoblotting demonstrated that the 5 antigen preparations share similar antigenic components. All preparations were similarly high in sensitivity and specificity, indicating that surface antigens could be satisfactorily used in our ELISA. Our ELISA using the glycine extract was compared with commercial H. pylori ELISAs developed by Bio-Rad Laboratories, USA (GAP ELISA), Roche, Switzerland (EIA 2G), and Whittaker Bioproducts, USA (Pyloristat). The HP+ve sera demonstrated high titers in commercial tests. 33/39 HP-ve sera were negative in Lund, Roche and Whittaker, while only 14 sera were detected negative in Bio-Rad. The remaining 6 HP-ve sera gave discordant results. All tests were high in sensitivity and specificity but Bio-Rad, using a purified antigen, had a specificity of only 56%.