Objective To prepare a recombinant pneumococcal surface protein A clade 4 ( PspA4) and to analyze its immunogenicity.Methods The gene encoding PspA4 protein was synthesized and inserted into pET-20b to construct the recombinant expression plasmid.The transformed E.coli strains carrying expression plasmid were induced to express PspA4 protein.ELISA was performed to analyze the ti-ters of PspA4-specific IgG in a mouse model.Results The recombinant PspA4 protein of high purity ( 90%) was successfully prepared.The titers of PspA4-specific antibody in mice received PspA4 immuniza-tion were 106 times higher than those of the blank control group, suggesting that the expressed PspA4 protein had the advantage of high immunogenicity.Conclusion This study suggested that the PspA4 protein might be used as one of the candidate protein for the development of pneumovax and laid a foundation for further in-vestigation on pneumococcal protein based vaccine.

Objective To screen and prepare a broad-spectrum monoclonal antibody against Strep-tococcus pneumoniae ( S. pneumoniae) surface protein A ( PspA) and to evaluate its potential in clinical prac-tice. Methods Hybridoma cells were screened and inoculated into the abdominal cavities of BALB/c mice to prepare antibodies in ascites. Monoclonal antibodies were obtained by ammonium sulfate precipitation and protein A affinity chromatography and then identified by SDS-PAGE and Western blot. Their specificity, iso-forms and killing activities in vitro were analyzed. Results A broad-spectrum monoclonal antibody that rec-ognized PspA subclasses 2, 3 and 4 was obtained. Its in vitro killing rate against S. pneumoniae reached 40. 3％. Conclusions A broad-spectrum monoclonal antibody that could specifically bind to PspA was suc-cessfully prepared with a strong in vitro killing activity. This study provided reference for clinical diagnosis of S. pneumoniae-related diseases, quality assessment of S. pneumoniae vaccines and further research on mono-clonal antibody therapeutics.