A novel linear B cell epitope of the porcine circovirus type 3 capsid protein identified by phage display technology

Porcine circovirus type 3 (PCV3) is endemic in swine worldwide and causes reproductive disorders, dermatitis and nephrotic syndrome, and multi-organ inflammation. PCV3 capsid protein (Cap) can self-assemble into virus-like particles (VLPs), and is an ideal candidate for vaccines and diagnostic reagents.In this study, the recombinant PCV3 Cap protein was successfully expressed in E. coli by deleting the nuclear localization sequence (NLS). The PCV3 VLPs were observed by transmission electron microscopy, and its immunogenicity was evaluated in six-week-old female BALB/c mice. A monoclonal antibody was named mAb 2D6, and demonstrated strong reactivity and specificity to PCV3 Cap. The purified mAb 2D6 was further used for bio-panning to select phage expressing specific epitopes from phage-displayed 7 mer-peptide library. A novel linear B-cell epitope, recognized by mAb 2D6, was identified at the amino acid region 47-53 of Cap. The phage peptide sequences were analyzed using multiple sequence alignment and evaluated by peptide ELISA. These results provide insights for developing diagnostic tools and potential vaccines for PCV3.