Expression of helicobacter pylori alpA gene in lactococcus lactis and its immunogenicity analysis

AIM To express Helicobacter pylori (Hp) alpA gene in a live delivery vehicle of lactococcus lactis (L. lactis) and assay the efficacy of the L. lactis-alpA oral vaccine in recipient mice. METHODS The alpA gene of Hp was amplified by PCR and cloned into the prokaryotic expression vector pNICE: sec. The recombinant vector pNICE: sec-alpA was transformed into Lactococcus lactis strain NZ9000. Then the engineered strain was induced to express recombinant alpA as shown by SDS-PAGE and Western blot. Female ICR mice (CV Grade) were randomly divided into 4 groups and administrated orally with PBS, L. lactis pNICE: sec, L. lactis pNICE: sec-alpA, and the inactivated Hp, respectively. After immunized seven times, the mice were detected for their alpA-specific IgG and IgA. RESULTS The alpA gene was obtained and successfully cloned into the vector pNICE: sec. The recombinant alpA protein (56,000) was accumulated in L. lactis after the induction of the nisin, accounting for 9.6% of the total bacterial protein. Western bolt confirmed that the alpA protein could be recognized specifically by the anti-Hp serum. The titer of anti-alpA IgG in the pNICE: sec-alpA group, comparable to that in the inactivated Hp group, was higher than that in the pNICE: sec group. The titer of anti-alpA IgA in the pNICE: sec-alpA group was higher than all other groups (P<0.05). CONCLUSION The oral administration of the engineered alpA-expressing L. lactis induced protective immunity against Hp. Our study provides a certain experimental basis for the use of L. lactis as an antigen-delivering vehicle for the development of Hp oral vaccines.