AIM:To construct a recombinant prokaryotic expressionvector inserted with Helicobacter pylori vacA gene andidentify the immunity of the expressed recombinant protein,and to determine prevalence of vacA-carrying/VacAexpressing H pylori isolates and seroprevalence of specificant-VacA antibody in H pylori infected patients.METHODS:Polymerase chain reaction technique was usedto amplify complete vacA gene of H pylori strain NCTC11637and to detect vacA gene in 109 H pylori isolates.Theamplification product of the complete vacA gene wassequenced after T-A cloning.A recombinant expressionvector inserted with a complete vacA gene fragment,namedas pET32a-vacA,was constructed.Expression of the targetrecombinant protein VacA (rVacA) was examined by SDS-PAGE.Western blot using commercial antibodies againstwhole cell of H pylori and an immunodiffusion assay usingself-prepared rabbit anti-rVacA antibody were applied todetermine immunoreaction and antigenicity of rVacA.TwoELISA methods were established to detect VacA expressionin H pylori isolates and the specific anti-VacA antibody insera from 125 patients infected with H pylori.RESULTS:In comparison with the reported correspondingsequences,homologies of nucleotide and putative aminoacid sequences of the cloned vacA gene were 99.82% and100%,respectively.The constructed recombinant prokaryoticexpression system efficiently produced rVacA,rVacA wasable to combine with the commercial antibodies againstwhole cell of H pylori and to induce the immunized rabbit toproduce specific antibody with an immunodiffusion titer of1:4.All tested H pylori isolates carried vacA gene,but only66.1% expressed VacA protein.Of the serum samples tested,42.4% were positive for specific anti-VacA antibody.CONCLUSION:A prokaryotic expression system of H pylorivacA gene was successfully constructed.The expressedrVacA can be used to detect specific anti-VacA antibody inhuman and to prepare antiserum in animals.The highfrequency of vacA gene in H pylori isolates,but with a lowfrequency of VacA expression and specific anti-VacA antibody in H pylori infected patients implies that VacA is not an idealantigen for H pylori vaccine. AIM: To construct a recombinant prokaryotic expression vector inserted with Helicobacter pylori vacA gene andidentify the immunity of the expressed recombinant protein, and to determine prevalence of vacA-carrying / VacAexpressing H pylori isolates and seroprevalence of specificant-VacA antibody in H pylori infected patients. METHODS : Polymerase chain reaction technique was used to amplify complete vacA gene of H pylori strain NCTC11637 and to detect vacA gene in 109 H pylori isolates. The product of the complete vacA gene was sequenced after TA cloning. A recombinant expression vector inserted with a complete vacA gene fragment, named as pET32a-vacA, was constructed. Expression of the target recombinant protein VacA (rVacA) was examined by SDS-PAGE. Western blot using commercial antibodies againstwhole cell of H pylori and an immunodiffusion assay using self-prepared rabbit anti-rVacA antibody were applied todetermine immunoreaction and antigenicity of rVacA.Two ELISA methods were establishe d to detect VacA expressionin H pylori isolates and the specific anti-VacA antibody insera from 125 patients infected with H pylori .RESULTS: In comparison corresponding sequences, homologies of nucleotide and putative aminoacid sequences of the cloned vacA gene were 99.82% and 100% , respectively. The constructed recombinant prokaryoticexpression system efficiently produced rVacA, rVacA was able to combine with the commercial antibodies against whole cell of H pylori and to induce the immunized rabbit toproduce specific antibody with an immunodiffusion titer of 1: 4.All tested H pylori isolates carried vacA gene , but only 66.1% expressed VacA protein. Of the serum samples tested, 42.4% were positive for specific anti-VacA antibody. CONCLUSION: A prokaryotic expression system of H pylorivacA gene was successfully constructed. The expressedrVacA can be used to detect specific anti -VacA antibody inhuman and to prepare antiserum in animals. The high frequency of vacA gene in H pylori isolates, but with a low frequency of VacA expression and specific anti-VacA antibody in H pylori infected patients implies that VacA is not an idealant for H pylori vaccine.