Objective To investigate the immunogenicity of DNA vaccine expressing pneumococcal surface adhesion A (PsaA)

and its effect against nasopharyngeal colonization of  Streptococcus pneumoniae in BALB/c mice.  Methods The genomic DNA of the standard Streptococcus pneumoniae strain D39 was isolated. PsaA gene open reading fragment was amplified by polymerase chain reaction (PCR) and cloned into the eukaryotic expression vector pcDNA3.1(+). Recombinant pcDNA3.1-PsaA was transfected into BHK

-21 cells using Lipofectamine

TM

2000

and the expression of PsaA protein was detected by Western blot.  Results RT-PCR and Western blot analysis of total cell extracts showed successful transcription and expression of PsaA in BHK-21 cells. The DNA vaccine pcDNA3.1-PsaA produced high levels of IFN-γ and high titers of serum IgG antibody in response to PsaA

and specific IgG2a isotype dominant responses (IgG1/IgG2a1). There were significantly fewer pneumococci in nasopharynx of mice immunized with the DNA vaccine pcDNA3.1-PsaA than those receiving plasmids pcDNA3.1(+) (P0.01).  Conclusion The DNA vaccine pcDNA3.1-PsaA induces specific humoral and cellular immunity in the immunized mice. The vaccine is effective in protecting mice against nasopharyngeal colonization of Streptococcus pneumoniae in BALB/c mice. The DNA vaccine encoding immunogenic protein of PsaA can be used as a candidate for novel vaccine design.