Characterization and potential use of truncated PCV2 capsid protein and its polyclonal antibody for diagnosis of PCV2 infections

Abstract:

As porcine circovirus 2 (PCV2) ORF2 encodes the major structural protein (capsid) that is closely related to the pathogenesis, the capsid (Cap) protein could be used as a target antigen for serological analysis. The immunoactivities of the truncated capsid proteins containing immunogenic epitopes of PCV2 (Cap2s) or PCV1 (Cap1s) expressed in Escherichia coli were described, as well as the characteristic of their polyclonal antibodies in diagnosis of PCV2 infection. Western blot analysis revealed that both Cap2s and Cap1s gave strong signals on nitrocellulose membranes to their corresponding polyclonal antibody. Furthermore, either PCV2-positive sera from PMWS cases or PCV1-positive swine sera could only recognize its relative polyclonal antibody. There was also no cross-reactivity between the two polyclonal antibodies when reacted with natural Cap proteins of viral particles on cells by immunofluorescence assay (IFA). Thus, an ELISA was then developed using PCV2 Cap as coating antigen to evaluate the sero-prevalence of PCV2 infection in pigs. The PCV2-positive rate ranged from 48.28% to 100% among different herds (n=13) with an average of 80.69% (209/259). These results indicate that Cap2s was type-specific and could be used as a discriminative antigen for monitoring PCV2 antibody in serum. The polyclonal antibodies were also useful for differential identification of PCV1 and PCV2 infection by immunohistochemistry.