Systemic cytokine profiles of mice vaccinated with naked DNAs encoding six open reading frame antigens of porcine circovirus type 2 (PCV2)

The objective of this study was to characterize the murine immune response to vaccination with DNAs encoding each of six porcine circovirus type 2 (PCV2) open reading frames (ORFs). After intramuscular vaccination with the naked DNAs, blood was taken on days post-infection (DPI) 7 and 35 and subjected to Bio-Plex cytokine assays. ORF3 elicited high levels of the pro-inflammatory cytokine TNF-α (P < 0.001) and decreased IL-12 levels (P < 0.001) on DPI 7, and was lethal for nine of the 15 vaccinated mice, which died on DPIs 4, 6, 9, and 10. The remaining six mice showed general prostration but then recovered. The clinical signs correlated with the systemic TNF-α and IL-12 levels. ORF1 vaccination elevated T-helper (Th)1 (IFN-γ; P < 0.001) and Th2 (IL-13; P < 0.05) cytokine levels on DPI 35, while ORF2 markedly elevated the expression of the humoral immunity- and Th-2-related cytokine IL-10 (P < 0.001) on DPI 35. These observations provide insights into the immune responses generated by each PCV2 ORF.