AIM: To investigate the frequencies of the expression of main protein antigens of Helicobacter pylori(H pylori)isolates, such as UreB, VacA, CagA1, HpaA, NapA, FlaA and FlaB and the production of specific antibodies in sera from H pylori-infected patients, and to understand the correlations among the different clinical types of chronic gastritis and peptic ulcer and the infection and virulence of H pylori.METHODS: H pylori strains in biopsy specimens from 157patients with chronic gastritis and peptic ulcer were isolated and serum samples from the patients were also collected.The target recombinant proteins rUreB, rVacA, rCagA1,rHpaA, rNapA, rFlaA and rFlaB expressed by the prokaryotic expression systems constructed in our previous studies were collected through Ni-NTA affinity chromatography.Rabbit antisera against rUreB, rVacA, rCagA1, rHpaA,rNapA, rFlaA and rFlaB were prepared by using routine subcutaneous immunization. By using ultrasonic lysates of the isolates as coated antigens, and the self-prepared rabbit antisera as the first antibodies and commercial HRP-labeling sheep anti-rabbit IgG as the second antibody,expression frequencies of the seven antigens in the isolates were detected by ELISA. Another ELISA was established to detect antibodies against the seven antigens in sera of the patients by using the corresponding recombinant proteins as coated antigens, and the sera as the first antibody and HRP-labeling sheep anti-human IgG as the second antibody respectively. Correlations among the different clinical types of chronic gastritis and peptic ulcer and the infection and virulence of H pylori were statistically analysed.RESULTS: In the 125 isolates of H pylori, the positive rates of UreB, VacA, CagA1, HpaA, NapA, FlaA and Flab were 100%, 65.6%, 92.8%, 100%, 93.6%, 100% and 99.2%respectively. In the 125 serum samples from the H pyloriinfected patients, the positive rates of antibodies against recombinant UreB, VacA, CagA1, HpaA, NapA, FlaA and Flab were 100%, 42.4%, 89.6%, 81.6%, 93.6%, 98.4%and 92.8% respectively. H pylori strains were isolated from 79.6% (125/157) of the biopsy specimens, but no close correlations among the H pylori infection frequencies and different types of chronic gastritis and peptic ulcer could be found (P＞0.05, x2 = 0.01-0.87). The VacA positive rate (82.40%) in the strains isolated from the specimens of patients with peptic ulcer and the anti-VacA positive rate (54.3%) in the sera from the patients were significantly higher than those (51.5%, 32.3%) from the patients with chronic gastritis (P＜0.01, x2 = 13.19; P＜0.05, x2 = 6.13).When analysis was performed in the different types of chronic gastritis, the VacA in the strains isolated from the specimems of patients with active gastritis showed a higher expression frequency (90.0%) than those from superficial (47.9%) and atrophic gastritis (30.0%) (P＜0.05, x2 = 5.93;P＜0.01,x2 = 7.50). While analysis was carried out in the strains isolated from the specimens with superficial (93.8%) and active gastritis (100%), NapA showed a higher expression frequency compared to that from atrophic gastritis (60.0%) (P＜0.01, x2 = 8.88; P＜0.05,x2= 5.00).CONCLUSION: The types of chronic gastritis and peptic ulcer and their severity are not associated with H pylori infection frequency but closely related to the infection frequency of different virulent H pylori strains. The optimal antigens for developing vaccine and diagnostic kit are UreB,FlaA, HpaA, FlaB, NapA and CagA1, but not VacA.