Oral immunization of mice with attenuated Salmonella typhimurium expressing Helicobacter pylori urease B subunit.

OBJECTIVE

To establish attenuated Salmonella typhimurium producing Helicobacter pylori (H. pylori) urease subunit B (UreB) and determine whether it could be used as an oral vaccine against H. pylori.

METHODS

H. pylori (SS1 strain) UreB gene fragment amplified by PCR was cloned into the prokaryotic expression vector pTC01 after sequencing, and then transformed into attenuated Salmonella typhimurium SL3261 to acquire SL3261/pTC01-UreB. The expression of H. pylori UreB in SL3261 was detected by Western blot. Twelve weeks after oral immunization of mice, antibody responses were evaluated using serum and intestinal fluid by ELISA assay. Interferon-gamma (IFN-gamma) and interleukin-10 (IL-10) in the supernatant of spleen cells culture were also assessed by ELISA. In vitro stability of pTC01-UreB plasmid in SL3261 was confirmed by growing in Luria Broth (LB) medium to 80 generations.

RESULTS

The UreB gene fragment amplified by PCR was consistent with the sequence of the H. pylori UreB as evidenced by sequence analysis. Enzyme digestion revealed that the correct pTC01-UreB was obtained. Western blot showed that a 61kDa protein was expressed in SL3261/pTC01-UreB, which could be recognized by anti-H. pylori UreB antiserum. After 80 generations of continuous culture, the recombinant plasmid pTC01-UreB was stable in SL3261 and had no obvious toxicity. Multiple oral immunizations with SL3261/pTC01-UreB could significantly induce H. pylori-specific mucosal IgA response as well as serum IgG response. Moreover, there were significant increases of IFN-gamma and IL-10 in the SL3261/pTC01-UreB group. Finally, no obvious side effects for mice and no change in gastric inflammation were observed.

CONCLUSION

Attenuated Salmonella typhimurium expressing H. pylori UreB may be used as oral vaccine against H. pylori infection.