Immune responses generated by Lactobacillus as a carrier in DNA immunization against foot-and-mouth disease virus

To exploit Lactobacillus acidophilus as a carrier in DNA immunization against foot-and-mouth disease virus (FMDV), a recombinant eukaryotic expression plasmid (pRc/CMV2-VP1-Rep. 8014) harboring pRc/CMV2 vector, the FMDV VP1 gene, and a replication origin from Lactobacillus plantarum ATCC 8014 strain was constructed. To detect the VP1 protein, pRc/CMV2-VP1-Rep. 8014 was expressed in PK 15 cells and transfected into a L. acidophilus SW1 strain (L. acidophilus SFMD-1). To evaluate the immunization effect of L. acidophilus SFMD-1, anti-FMDV VP1 antibody, T-cell proliferation, antigen-specific delayed-type hypersensitivity (DTH), and tissue distribution were investigated using intramuscular, intraperitoneal, intranasal, and oral administration delivery routes. The results showed that L. acidophilus SFMD-1 was able to elicit a detectable antibody level on day 21. The VP1 antibody levels induced by L. acidophilus SFMD-1 and commercial inactivated FMDV vaccine rose rapidly to 0.84 and 0.70, respectively, by day 42, then sustained a high level by day 49. The route of administration had an impact on the magnitude of the systemic antigen-specific IgG responses, with intramuscularly applied L. acidophilus SFMD-1 generating the greatest FMDV VP1 antibody response, followed by intraperitoneal, intranasal, and oral administration delivery routes. Using the T-cell proliferation assay, the stimulation index of a group immunized with L. acidophilus SFMD-1 reached 2.78 versus 5.08 in a group immunized with pRc/CMV2-VP1-Rep. 8014 plasmid. Mice immunized with L. acidophilus SFMD-1 were able to induce T-cell-mediated antigen-specific DTH. In addition, the VP1 gene was detected in the muscle, kidney, spleen, and heart, but not in the liver. The results demonstrate clearly that Lactobacillus as a carrier is a promising approach of DNA vaccination, and is a potentially guard against FMDV.