Expression of PCV2d Capsid Protein in Escherichia coli and its Evaluation for Serodiagnosis of Porcine Circovirus Infection

Abstract

The porcine circovirus 2 (PCV2) is one of the most economically significant swine pathogens, causing PCVAD as well as impaired reproductive efficiency, stillbirth, and weight loss in infected pig populations. The PCV2 ORF2 gene encodes capsid protein (cap protein), which has 233 amino acids (AA) in PCV2a/2b and an additional lysine residue at the C-terminus in PCV2d. In this study, we created a PCV2d capsid sequence (ORF2) for expression in Escherichia coli. His tag chromatography method was used to purify the protein, and western blot was used to detect protein expression. In this study, an indirect enzyme-linked immunosorbent assay (I-ELISA) based on the PCV2d ORF2 protein was developed. The best antigen, serum, and goat anti-porcine IgG conjugate dilutions were 1:1500 (3.245 µg/ml), 1:320, and 1:1600, respectively. The estimated cut-off value was 0.9885, and its analytical sensitivity was 1:2400. Except for PCV2a, PCV2b, and PCV2d antisera, the results of specific evaluation revealed that these antisera did not cross-react with any other common porcine viral pathogens, indicating that this method can be used to detect porcine circovirus infection in pig.