Porcine circovirus type 2 (PCV2) is the causative agent of postweaning multisystemic wasting syndrome (PMWS), porcine dermatitis and nephropathy syndrome (PDNS), and reproductive failure and causes economic losses in the domestic swine industry. The decoy epitope (169–180 amino acid (aa)) of the PCV2 capsid (Cap) protein is an immunodominant epitope and diverts the immune response away from protective epitopes. The mixed infection of PCV2 and porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most common co-infections in the pig industry and shows more severe clinical symptoms. Linear B-cell antigenic epitopes of PRRSV GP3 epitope Ⅰ (61–72aa) and PRRSV GP5 epitope Ⅳ (187–200aa) efficiently elicited neutralizing antibodies against PRRSV. The recombinant baculovirus expressing the Cap protein (Bac-Cap) was modified by replacing the decoy epitope of the Cap protein with either the PRRSV GP3 epitope Ⅰ, the PRRSV GP5 epitope Ⅳ, or the PRRSV GP3 epitope Ⅰ- GP5 epitope Ⅳ to produce the recombinant baculoviruses Bac-Cap-GP3, Bac-Cap-GP5 and Bac-Cap-GP35. The four recombinant baculoviruses were successfully established and characterized as demonstrated with western blot analysis and immunofluorescence assay. Immunogenicities of the four recombinant baculoviruses in mice were tested in sera harvested at 21 and 42 days post-primary immunization. The titers of antibodies in the sera were determined by a PCV2-specific enzyme-linked immunosorbent assay (ELISA) and a serum neutralization assay. The serum IFN-γ levels were measured by indirect ELISA. The results showed that Bac-Cap-GP3, Bac-Cap-GP5, and Bac-Cap-GP35 elicited higher GP3/GP5 and Cap antibody titers than the Bac-Cap. Virus neutralization test also confirmed that the serum from the Bac-Cap-GP3 immunized mice had high levels of the both PCV2 and PRRSV neutralization antibodies. These findings collectively demonstrated that substituting the decoy epitope of the PCV2 capsid substituted with PRRSV epitopes could be developed into an effective vaccine against PCV2.

猪圆环病毒2型（PCV2）是断奶后多系统消耗综合症（PMWS），猪皮炎和肾病综合症（PDNS）以及生殖衰竭的病原体，并在国内养猪业中造成经济损失。PCV2衣壳（Cap）蛋白的诱饵表位（169-180个氨基酸（aa））是一种免疫优势表位，可将免疫应答从保护性表位转移出去。PCV2和猪繁殖与呼吸综合征病毒（PRRSV）的混合感染是养猪业中最常见的共同感染之一，并且表现出更严重的临床症状。PRRSV GP3抗原表位Ⅰ（61-72aa）和PRRSV GP5抗原表位Ⅳ（187-200aa）的线性B细胞抗原表位有效诱导了针对PRRSV的中和抗体。通过用PRRSV GP3表位Ⅰ，PRRSV GP5表位Ⅳ，PRRSV GP3表位Ⅰ-GP5表位Ⅳ替换Cap蛋白的诱饵表位来修饰表达Cap蛋白的重组杆状病毒（Bac-Cap）。重组杆状病毒Bac-Cap-GP3，Bac-Cap-GP5和Bac-Cap-GP35。成功构建了四种重组杆状病毒，并进行了Western印迹分析和免疫荧光分析所证实。在初次免疫后第21天和42天收集的血清中测试了四种重组杆状病毒在小鼠中的免疫原性。通过PCV2特异性酶联免疫吸附测定（ELISA）和血清中和测定来确定血清中抗体的效价。通过间接ELISA测量血清IFN-γ水平。结果显示Bac-Cap-GP3，Bac-Cap-GP5和Bac-Cap-GP35引起的GP3 / GP5和Cap抗体滴度高于Bac-Cap。病毒中和测试还证实，来自Bac-Cap-GP3免疫小鼠的血清中PCV2和PRRSV中和抗体水平都很高。这些发现共同表明，用PRRSV表位代替PCV2衣壳的诱饵表位可以被开发成针对PCV2的有效疫苗。