Potent neutralization activity against type O foot-and-mouth disease virus elicited by a conserved type O neutralizing epitope displayed on bovine parvovirus virus-like particles

In this study, ten sites on the N terminus and different surface variable regions (VRs) of the bovine parvovirus (BPV) VP2 capsid protein were selected according to an alignment of its sequence with that of the BPV-1 strain HADEN for insertion of the type O foot-and-mouth disease virus (FMDV) conserved neutralizing epitope 8E8. Ten epitope-chimeric BPV VP2 capsid proteins carrying the 8E8 epitope were expressed in Sf9 cells, and electron micrographs demonstrated that these fusion proteins self-assembled into virus-like particles (VLPs) with properties similar to those of natural BPV virions. Immunofluorescence assay (IFA) and Western blot analysis demonstrated that each of the ten epitope-chimeric VLPs reacted with both anti-BPV serum and anti-type O FMDV mAb 8E8. These results indicated that insertions of the 8E8 epitope at these sites on the BPV VP2 protein did not interfere with the immunoreactivity of VP2 or VLP formation, and that the exogenous epitope 8E8 was correctly expressed in BPV VLPs. In addition, anti-BPV IgG antibodies were induced in mice by intramuscular inoculation with each of the ten chimeric VLPs, indicating that the immunogenicity of the chimeric VLPs was not disrupted. Importantly, potent anti-FMDV viral neutralizing (VN) antibodies, which exhibited the highest titre of 1 : 176, were induced by two chimeric VLPs, rBPV-VLP-8E8(391) and rBPV-VLP-8E8(395), in which the 8E8 epitope was inserted into positions 391/392 and 395/396, respectively, in the VR VIII of BPV VP2. Our results demonstrated that the 391/392 and 395/396 positions in the VR VIII of the BPV VP2 protein can effectively display a foreign epitope, making this an attractive approach for the design of nanoparticle-vectored and epitope-based vaccines.