Intragastric Administration of Lactobacillus casei Expressing Bovine Rotavirus VP7 Protein Induced Specific Antibody Production

The aim of this study is to explore the mucosal and systemic antibody immune responses induced by recombinant L.casei expressing the major immunoprotective antigen VP7 of bovine rotavirus (BRV). Two inducible expression vectors containing the antigenic dominant region of VP7 gene, pPG-1-VP7 (cell-surface expression vector) and pPG-2-VP7 (secretory vector), were constructed and electrotransformed into L. casei 393 to obtain positive recombinant bacteria designated rLc::pPG-1-VP7 or rLc::pPG-2-VP7. The expressions of VP7 protein induced by 2% lactose in MRS media were confirmed by western blot and indirect immunofluorescent staining using anti-VP7 antibody. Oral immunization of mice with the recombinant strains significantly increased anti-VP7 sIgA level in mouse vaginal lavages and feces samples, and anti-VP7 IgG level in serum compared with empty plasmid transformed bacteria. Results of neutralization assay clearly indicated that serum antibodies induced by oral vaccination have neutralization activity against BRV in vitro. The neutralizing titers are 1:62.9 and 1:50.6 for rLc::pPG-1-VP7 and rLc::pPG-2-VP7, respectively. Our results demonstrated that Lactobacillus casei expressing rBRV-VP7 have application potentials in producing oral vaccine against BRV.