Epitope screening of the PCV2 Cap protein by use of a random peptide-displayed library and polyclonal antibody

Capsid protein (Cap), the only structural protein of porcine circovirus 2 (PCV2), is involved in the host protective response and is a target for vaccine development. To find a rapid and easy way to fully map the antigenic epitopes of Cap, purified Cap-specific polyclonal antibodies were used to screen a random heptapeptide phage display library. After three rounds of screening, twenty phage clones that had binding activity to Cap-specific antibodies (tested by phage ELISA) were sequenced. When the inserted amino acid sequences were aligned with the Cap protein sequence, eight core regions in Cap (50SRTFGYT56, 62VRTPSW67, 68AVDMMR73, 79FLPPGG84, 86SNPRSVPF93, 102KVEFWP107, 119GSSXXXLDDN128 and 229PPLNP233) were identified, three of which (50SRTFGYT56, 86SNPRSVPF93 and 102KVEFWP107) for the first time. Nine phagetopes representing the eight regions were chosen to immunize Kunming mice. All except minotopes 50SRTFGYT56 and 229PPLNP233 induced antibodies against PCV2 when injected into Kunming mice.