A candidate DNA vaccine encoding a fusion protein of porcine complement C3d-P28 and ORF2 of porcine circovirus type 2 induces cross-protective immunity against PCV2b and PCV2d in pigs

Fig. 1. Construction of the plasmids PVAX1-ORF2 and PVAX1-ORF2-C3d-P28.3 (a) Top: the ORF2 construct that was used as a vaccine insert; Bottom: the ORF2-C3d-P28.3 construct that was used as a vaccine insert. Linkers composed of two repeats of four glycines and a serine [(G4S)2] were fused at the junctures of ORF2 and C3d and between each C3d repeat. b Restriction digest of PVAX1-ORF2 and PVAX1-ORF2-C3d-P28.3. Lane 1: DL2000 marker; lane 2: PVAX1-ORF2 digested with Nhe I/Hind III; lane 3: PVAX1-ORF2-C3d-P28.3 digested with Nhe I/Hind III; lane 4: DL5000 marker

Fig. 2. In vitro expression of DNA vaccine constructs. DNA vaccine constructs were transfected into PK-15 cells and then stained with rabbit polyclonal anti-Cap of PCV2 followed by FITC-labelled goat anti-rabbit antibody. a negative control; (b) pVAX1-ORF2; (c) pVAX1-ORF2-C3d-P28.3

Fig. 3. Production of PCV2 antibodies in pigs after vaccination and infection with PCV2b or PCV2d viruses. Pigs in each of seven groups (n = 5 per group) were vaccinated on day 0, boosted on day 21, and infected with PCV2 on day 35. The mean sample-to-positive (S/P) ratio of each group at different days post vaccination were measured weekly by PCV2 ELISA as an indication of the host response. Different superscripts (a,b,c,d,e) indicate significant differences among groups. (p < 0.05)

Fig. 4. PCV2 DNA in sera after vaccination and infection of pigs with PCV2b or PCV2d. The PCV2b or PCV2d genomic copies in serum were measured at days 7, 14, and 21 after virus challenge and were expressed as the mean log10 quantities of 5 pigs per group. No DNA was detected prior to viral challenge. Different superscripts (a,b,c,d) indicate significant differences among groups. (p < 0.05)

Fig. 5. PCV2-specific cell-mediated immune responses to PCV2b and PCV2d are stimulated by vaccination. The numbers of PCV2-specific interferon-γ secreting cells (IFN-γ-SC)/106 peripheral blood mononuclear cells (PBMC) were assessed weekly after vaccination (on day 0 and 21) and PCV2 infection (on day 35). Different superscripts (a,b,c,d,e) indicate significant differences among groups. (p < 0.05)