AIM： To study the immunological protective effect of H pylori vaccine with chitosan as an adjuvant and its mechanism. METHODS： Female BALB/c mice were randomly divided into seven groups and orally immunized respectively with PBS, chitosan solution, chitosan particles, H pylori antigen, H pylori antigen plus cholera toxin （CT）, H pylori antigen plus chitosan solution, Hpylori antigen plus chitosan particles once a week for four weeks. Four weeks after the last immunization, the mice were challenged twice by alive Hpylori （1 × 10^9 CFU/mL） and sacrificed. Part of the gastric mucosa was embedded in paraffin, cut into sections and assayed with Giemsa staining. Part of the gastric mucosa was used to quantitatively culture Hpylori. EUSA was used to detect cytokine level in gastric mucosa and anti- Hpylori IgG1, IgG2a levels in serum. RESULTS： In the groups with chitosan as an adjuvant, immunological protection was achieved in 60% mice, which was significantly higher than in groups with H pylori antigen alone and without H pylori antigen （P 〈 0.05 or 0.001）. Before challenge, the level of IFN and IL-12 in gastric mucosa was significantly higher in the groups with chitosan as an adjuvant than in the control group and the group without adjuvant （P 〈 0.05 or 0.005）. After challenge, the level of IFN and IL-12 was significantly higher in the groups with adjuvant than in the groups without adjuvant and antigen （P 〈 0.05 or 0.001）. Before challenge, the level of IL-2 in gastric mucosa was not different among different groups. After challenge the level of IL-2 was significantly higher in the groups with adjuvant than in the control group （P 〈 0.05 or 0.001）. Before challenge, the level of IL-10 in gastric mucosa was significantly higher in the groups with chitosan as an adjuvant than in other groups without adjuvant （P 〈 0.05 or 0.01）. After challenge, the level of IL-10 was not different among different groups. Before challenge, the level of IL-4 in gastric mucosa was significantly
