The construction of recombinant Lactobacillus casei expressing BVDV E2 protein and its immune response in mice

•Construction of Bovine Viral Diarrhea Virus (BVDV) E2 gene expressing pELX1-E2 system in L. casei.•Strong humoral, cellular and local immune responses was found in mice induced by the recombinant strain.•Intranasal administration was found most effective route of vaccination.•Active protection followed by viral challenge was found from viral load and neutralizing antibody detection.•Constructed recombinant L. casei may establish the ground for developing promising recombinant mucosal vaccine against BVD. Bovine viral diarrhea virus (BVDV) is the etiological agent of BVD causes substantial economic losses and endemic in world-wide cattle population. Mucosal immunity plays an important role in protection against BVDV infection and Lactobacillus casei is believed as an excellent live vaccine vector for expressing foreign genes. In this study, we have constructed a novel recombinant L. casei/pELX1-E2 strain expressing the most immunogenic E2 antigen of BVDV; using growth phage dependent surface expression system pELX1. The expression of E2 protein was verified by SDS-PAGE, Western blotting, and Immunofluorescence microscopic analysis. The immune responses triggered by the E2 producing recombinant L. casei were evaluated in BALB/c mice revealed that oral and intranasal (IN) administration of the recombinant strain was able to induce a significantly higher level of specific anti-E2 mucosal IgA and serum IgG as well as the greater level of cellular response by IFN-γ and IL-12 than those of intramuscular (IM) and control groups of mice. However, IN inoculation was found the most potent route of immunization. The ability of the recombinant strain to induce serum neutralizing antibody against BVDV and reduced viral load after viral challenge indicated better protection of BVDV infection. Therefore, this recombinant L. casei expressing E2 could be a safe and promising mucosal vaccine candidate against BVD.