Recombinant Lactobacillus casei Expressing Capsid Protein VP60 can Serve as Vaccine Against Rabbit Hemorrhagic Disease Virus in Rabbits

Wang, Li; Xia, Tian; Guo, Tiantian; Ru, Yi; Jiang, Yanping; Cui, Wen; Zhou, Han; Qiao, Xinyuan; Tang, Lijie; Xu, Yigang; Li, Yijing

An effective oral vaccine should induce both systemic and mucosal immune responses. Thus, we evaluated the immunogenicity of orally administered pPG-eGFP-VP60/LC393 in rabbits. The multiple immunization procedure of recombinant Lactobacillus was employed in this study was due to the amounts of recombinant Lactobacillus adhered to the intestinal mucosa were decreased with the time [57] . The immune effect of the multiple immunization procedure of recombinant Lactobacillus has been confirmed in the previous studies [31, 35] . The rabbits were immunized with inactivated vaccine according to the instruction. Serum-derived IgG can appreciably contribute to immune defense by reducing the ability of pathogens to cross intestinal mucosa, thereby limiting the systemic spread of invasive organisms [58] . We detected substantially increased levels of anti-RHDV IgG in rabbits orally immunized with pPG-eGFP-VP60/LC393; these levels increased rapidly following booster immunization. sIgA, a major immunoglobulin in mucosal immune responses, protects against pathogen invasion at mucosal sites [59] . Therefore, sIgA levels can be used to evaluate the protective efficacy of vaccines [60] . In the present study, we detected high levels of antigen-specific mucosal sIgA in the nasal washes, vaginal lotions, tears, and feces of rabbits orally immunized with pPG-eGFP-VP60/LC393. Recombinant L. casei pPG-eGFP-VP60/LC393 induced a higher level of sIgA compared with that induced by the inactivated virus vaccine, indicating that L. casei pPG-eGFP-VP60/LC393 was more efficient at eliciting mucosal immune responses, and there were almost no significant differences of sIgA and IgG antibody levels in the experimental animals administered with pPG/L. casei 393 and PBS, which have been confirmed in our previous studies [31, 35, 51] . Previous studies also have shown that oral vaccines elicit stronger mucosal immune responses than do injected vaccines [46] . In our present study, we have shown that oral vaccination with recombinant L. casei pPG-eGFP-VP60/LC393 can strongly induce anti-RHDV systemic and mucosal immune responses.