Studies on the Immune Responses Induced by the CpG-enhanced Plasmid DNA Vector Encoding Hantavirus Nucleiocapsid Protein

Bacterial and synthetic DNA containing CpG dinucleotides in specific sequence contexts are being tested as immune adjuvants in many disease settings. To study the immune responses induced by the CpG-enhanced plasmid DNA vector encoding hantavirus nucleiocapsid protein. BALB/c mice were immunized three times by intramuscular inoculations of the recombinant eukaryotic expression vector pcDNA3.1+S(ISS) at 2-wk intervals. To evaluate the humoral and cellular immune responses, antigen-specific lymphocyte proliferation and antibody production were assayed by MTT method and ELISA,respectively. In addition,the level of interleukin-4 and interferon-γ in the splenic lymphocytic cultured supernatant were detected with ELISA kit at various times. We found that the group immunized with pcDNA3.1+S(ISS) had more Ab response against NP compared with the control group over the period, specially at 35d and 42d,after the primary immunization. The antibody mean titre of the group immunized with pcDNA3.1+S(ISS) was increased to about 1:90 at 42d,significantly higher than that of the group immunized with pcDNA3.1+S alone, in which the mean titre was about 1:70. The stimulation index of the groups immunized with pcDNA3.1+S (ISS), pcDNA3.1+S and pcDNA3.1 were 1.67,1.43 and 0.797,respectively. The recombinant plasmid pcDNA3.1+S (ISS) markedly increased the production of IFN-γ but had no influence on the production of IL-4 compared with pcDNA3.1+S alone. These data indicated that CpG-enhanced plasmid induced augmented immune responses and could be used to vaccinate against pathogens requring a strong cellular response for protection.