Abstract: The recombinant expression vector plasmid CpG-pVAX1-E was transfected into COS-7 cells by using lipofectamine methods.The ORF5 mRNA of transfected cells were detected by RT-PCR. The transient expression of PRRSV SD2 ORF5 nucleocapsid protein was detected by indirect immunofluorescence assay(IFA). In some transfected COS-7 cells, the green fluorescence was showed.The recombinant expression plasmid was inoculated into SPF mice.The antibody ies specific for E protein in serum were confirmed by ELISA. T lymphocyte proliferation test(MTT) were used to detect the number of CD4+ 、CD8 + and the T lymphocyte proliferation in peripheral blood of mice vaccinated. The results showed that the recombinant plasmid induced　CpG-pVAX1-E could induce higher response of cellular immune response and specific humoral immune responses in mice . CpG-ODN was effective adjuvant which could significantly enhance the immunogenicity of PRRSV SD2 ORF5 DNA vaccine.

Key words: Porcine reproductive and respiratory syndrome virus（PRRSV）SD2, Eukaryotic expression vector, E Gene, Immunogenicity