Identification of a dominant linear epitope on the VP2 capsid protein of porcine parvovirus and characterization of two monoclonal antibodies with neutralizing abilities.

Porcine parvovirus (PPV) is a major cause of reproductive failure in swine, and has caused huge losses throughout the world. The structural viral protein VP2, which is able to self-assemble into empty capsids, known as virus-like particles (VLPs), is crucial to induce PPV-specific neutralizing antibodies and protective immunity. In this study, twelve monoclonal antibodies (mAbs) against PPV were generated. The mAbs were characterized by indirect enzyme-linked immunosorbent assay (ELISA), western blotting (WB) and virus neutralization (VN) assay. Two mAbs were defined to be able to neutralize the standard PPV 7909 strain. Subsequently, peptide scanning was applied to identify linear epitopes. The peptide, ESGVAGQMV was defined as a precise linear epitope. Results from structural analysis showed that the epitope was exposed on the virion surface. Multiple sequence alignment analysis indicated that peptide ESGVAGQMV was not completely conserved, with a higher amino acid mutation rate at G, V and A position. Alanine-scanning mutagenesis further revealed that residues E, S, G, V and G were the core sites involved in antibody recognition. These findings may facilitate further understanding the function of the VP2 protein and development of diagnostic tools.