Immune protection and mechanism of plasmid DNA encoding Gglycoprotein of respiratory syncytial virus(RSV)
Objective To construct a plasmid DNA encoding G glycoprotein of respiratory syncytial virus(RSV) and investigate the protective immune response against RSV infection. Methods Recombinant plasmid DNA of pcDNA3.1~G was constructed by standard RT-PCR based cloning procedure. The immunogenicity of recombinant G protein transiently expressed in HEK293 cells was detected by Western blot. BABL/c mice were intramuscularly immunized with pcDNA3.1~G. Samples of lung, sera, bronchoalveolar lavage fluid(BALF) were collected before and after RSV challenge; virus titer in lung was detected by viral titration; sections of paraffin embedding lung tissues were stained by haematoxylin and eosin(HE) for histological analyses; sera anti-RSV IgG levels were examined by ELISA; Th1/Th2 cytokine were detected by ELISA kit, the T lymphocyte subsets of BALF was determined by immunefluorescence staining followed by flow cytometry. Results Plasmid DNA of pcDNA3.1~G was successfully constructed. The expressed target protein possesses immunogenicity. After challenge, pcDNA3.1~G immunized mice presented relieved pathological changes in lung as well as reduced lung viral titers. The RSV specific IgG was detected in sera of immunized mice. There was significantly increased number of CD25~+CD4~+ T cells in mice BALF. Conclusion We constructed a pcDNA3.1~G plasmid DNA vaccination which can induce evident protective cellular immunity against RSV infection in mice with the increased number of CD25~+CD4~+ T cell subpopulation. 
 
Key words: 
Respiratory syncytial virus;  G glycoprotein;  Recombinant plasmid;  T lymphocyte