Immunogenicity and protective efficacy of orally administered recombinantLactobacillus plantarumexpressing VP2 protein against IBDV in chicken

To develop an effective oral vaccine against the very virulent infectious bursal disease virus (vvIBDV), we generated two recombinant Lactobacillus plantarum strains (pPG612‐VP2/LP and pPG612‐T7g10‐VP2/LP, which carried the T7g10 translational enhancer) that displayed the VP2 protein on the surface, and compared the humoral and cellular immune responses against vvIBDV in chickens. We genetically engineered the L. plantarum strains pPG612‐VP2/LP and pPG612‐T7g10‐VP2/LP constitutively expressing the VP2 protein of vvIBDV. We found that the T7g10 enhancer efficiently upregulates VP2 expression in pPG612‐T7g10‐VP2/LP. Orally administered, pPG612‐T7g10‐VP2/LP exhibited significant levels of protection (87·5%) against vvIBDV in chickens, indicating improved immunogenicity. Chickens in the pPG612‐T7g10‐VP2/LP group produced higher levels of interferons (IFN‐γ) and interleukins (IL‐2 and IL‐4) than those in the pPG612‐VP2/LP group. CD8+ and CD4+ lymphocyte counts indicated greater stimulation in the pPG612‐T7g10‐VP2/LP group (13·3 and 21·0% respectively) than in the pPG612‐VP2/LP group (10·4 and 14·0% respectively). Thus, pPG612‐T7g10‐VP2/LP could induce strong humoral and cellular immune responses against vvIBDV. The recombinant L. plantarum that expresses pPG612‐T7g10‐VP2 is a promising candidate for oral vaccine development against vvIBDV. The recombinant Lactobacillus delivery system provides a promising strategy for vaccine development against vvIBDV in chickens.