Protective immunity against porcine circovirus 2 by vaccination with ORF2-based DNA and subunit vaccines in mice

The protective immune response against porcine circovirus 2 (1 infection in mice was characterized using flow cytometric analysis (FCM), assays of antibody (of different IgG isotypes) and viraemia, and histopathological examination. An open reading frame 2 plasmid (pORF2) and the capsid protein (Cap) of i were used as DNA and subunit vaccines, respectively. In FCM analysis, although pORF2 and Cap alone showed comparable efficacy in eliciting lymphoproliferative responses and Cap-specific CD4+ T cells, i was superior to the Cap protein in triggering CD8+ T cells. A virus neutralization assay showed that i evoked stronger recall virus-neutralizing (Vi antibody responses than the Cap protein on i challenge. Correspondingly, VIN antibody kinetics coincided with those of Cap-specific IgG2a, but not with the kinetics of IgG and IgG1. Following virus challenge, real-time i and histopathological analysis confirmed that only low viral DNA loads and mild microscopic lesions appeared in pORF2-immunized mice. These findings indicate that CD8' T cells and VN antibody responses correlating mainly with Cap-specific IgG2a play crucial roles in protecting against 1 infection, and that the protective immunity induced by the i plasmid is superior to that induced by the i Cap protein.