Gastritis in urease-immunized mice after Helicobacter felis challenge may be due to residual bacteria.

Oral immunization with recombinant Helicobacter pylori urease (rUre) coadministered with a mucosal adjuvant protects mice against challenge with Helicobacter felis. In this study, the duration of protection and gastritis after challenge were characterized at sequential time intervals up to 1 year. Outbred Swiss-Webster mice were orally immunized with rUre plus adjuvant and examined for the presence of H. felis infection and leukocyte infiltration into the gastric mucosa. When defined by gastric urease activity, 70%-95% of rUre-immunized mice were protected for between 2 and 57 weeks. Challenge with H. felis increased the inflammatory response in the gastric mucosa of rUre-immunized mice, which also had elevated CD4+ and CD8+ T cells. The CD8+ cells represented a population of gastric intraepithelial cells, which expressed the mucosal alpha E-integrin. Epithelial changes consisting of parietal cell loss and hyperplasia of the epithelium occurred in approximately 20% of the mice. Antimicrobial triple therapy significantly decreased the degree of gastritis and epithelial alteration in the stomach. These results indicate that oral immunization of mice with rUre produces a long-lasting inhibition of H. felis infection but that residual bacteria may produce a persistent lymphocytic infiltration under these experimental conditions.