含变链菌SBR基因的双启动子质粒pCN-SSIE的构建及其免疫原性检测

Construction of a dual-promoter DNA expression plasmid pCN-SSIE harboring gene encoding SBR of Streptococcus mutans and verification of its immunogenicity as DNA vaccine

目的:构建含有编码变形链球菌致龋毒力因子SBR基因的双启动子防龋DNA疫苗pCN-SSIE,以减毒沙门菌为载体进行高效黏膜免疫。方法:通过PCR扩增编码变形链球菌表面蛋白抗原的唾液结合区段(SBR)基因和增强型绿色荧光蛋白(EGFP)基因,将SBR基因插入到双启动子表达载体pCMVnir中,在SBR基因上游和下游依次插入人工合成的tPA信号肽基因序列、核糖体内部进入位点(IRES)基因和EGFP基因,构建质粒pCN-SSIE。通过DNA测序和酶切分析证明,双启动子表达质粒pCN-SSIE构建成功后,再用该质粒转化减毒沙门菌SL3261和转染CHO细胞,检测SBR在原核细胞和真核细胞中的表达状况,最后用pCN-SSIE裸质粒通过肌内注射免疫小鼠,检测其血清中的抗SBR特异抗体。结果:DNA测序和酶切分析均证明,构建的双启动子表达质粒pCN-SSIE开放读码框架正确;质粒在原核和真核细胞中均能正常表达;在免疫小鼠的血清中检测到了高水平的抗SBR特异IgG。结论:构建成功双启动子表达质粒pCN-SSIE,在体外真核和原核细胞中均能正常表达,用其作为DNA疫苗免疫动物,可诱导明显的免疫应答。

PURPOSE： To construct a dual-promoter expression plasmid that harbors the target gene encoding SBR of Streptococcus mutans and can be applied as DNA vaccine especially suitable for using attenuated Salmonella as delivery vector to elicit effective mucosal immune responses because of its advantage of possessing dual-promoter. METHODS： Genes encoding SBR and green fluorescence protein gene （EGFP） were amplified by PCR and inserted to the proper sites of vector pCMVnir. Then IRES sequence was inserted between the genes coding for SBR and EGFP. Furthermore, a DNA fragment encoding tissue-type plasminogen activator （tPA） signal peptide was fused to the 5＇ end of target gene. Thereby, construction of the dual-promoter expression plasmid pCN-SSIE was completed and then the plasmid was analyzed with DNA sequencing and endonuclearase digestion mapping. The expressions of SBR protein by attenuated Salmonella SL3261 and CHO cell transformed or transfer＇ted by the plasmid were tested respectively. Finally, BALB/c mice were immunized through injecting intramuscularly with plasmid pCN-SSIE and anti-SBR specifie IgG in serum was tested. RESULTS： Both DNA sequencing and endonuclearase digestion mapping showed that the construction of pCN-SSIE was successful with its open reading frame being correct. The expressions of SBR protein in transformed attenuated Salmonella SL3261 and transfected CHO were detected, and anti-SBR specific IgG levels in serum of immunized mice were markedly higher than the control. CONCLUSION： The construction of the dual-promoter expression plasmid pCN-SSIE was successful and the plasmid can express in prokaryocyte and eukaryocyte and elicit dramatic immune response when applied as DNA vaccine in experimental animal. Supported by National Natural Science Foundation of China （Grant No. 30171010）.