Prevalence of cytotoxin-producing Helicobacter pylori (Hp) strains detected by the anti-CagA Assay (ACAA) among patients with peptic ulcer disease and controls

Abstract

Background ELISA detecting anti-CagA protein antibody was previously shown to yield a sensitivity of 96.2% and a specificity of 96.6% for confh'mation of cytotoxin-producing (CT +) Hp infection. The ACAA was performed in this study to document the prevalence of CT+ Hp infection among the Chinese ulcer patients and controls in Hong Kong. Materials & methods A cohort of lip+ duodenal ulcer (DIY), gastric ulcer (GU) or asymptomatic normals (N) were selected for this study. Sera from patients with DU (155 males [m] & 42 females [fl, mean age 41.7 yrs), GU (57 m & 9 f, mean age 52.7 yrs), or N (52 m & 48 f, mean age 34.9 yrs) were used for ACAA. CagA (recombinant fragment) protein (1.25 ug/ml in carbonate buffer [pH 9.6]) was coated onto ELISA wells overnight at 4°C. The wells were then quenched by PBS (pH7.4)/Tween 20 (0.1%) with 1$ BSA for 1 hr at room temperature (RT). Diluted serum (1 in 75) in duplicates were added for incubation for 2 hr at RT. The wells were washed and further incubated in peroxidase-tagged goat anti-buman IgG antibody (1 in 2000) for 90 minutes at RT. The bound 2nd antibody was identified by p-Nitrophenylphosphate. Finally, the plates were read at 405rim. 100 sera from the N and documented Hp- were used to determine the cut off level (mean + 2SD). Repeat assays on 6 negative and 6 positive controls were performed to test the reproducibility. Results The percentage of ACAA+ in these subjects were: DU (n=197) GU (n=66) N (n=100) p value ACAA+ 84 77.3 29.0 *<0.01 (*DU vs N and GU vs N). The ACA.A was highly reproducible (92%). Conclusions CT+/-/p is present in both DU and GU patients significantly more frequent than the N controls. These results would support CT+ lip strains to be more ulcerogenic and that the CT must have played one of the major direct or indirect offensive roles in the gastroduodenal mucosae.