甲型副伤寒沙门菌h1a-spaO融合基因构建及其表达产物免疫保护作用

Construction of a fusion gene encoding h1a-spaO of Salmonella paratyphi A and analysis of immuno-protective effects of the recombinant protein

目的：构建甲型副伤寒沙门菌h1a-spaO融合基因及其原核表达系统，确定重组表达产物rH1a-SpaO免疫保护作用。方法采用柔性肽序列连接引物PCR构建并扩增h1a与spaO基因的融合基因h1a-spaO，T-A克隆后测序。采用常规基因工程方法构建h1a-spaO融合基因原核表达系统，SDS-PAGE检测其rH1a-SpaO表达情况。采用Westernblot鉴定rH1a-SpaO抗原性和免疫反应性，微量肥达试验确定rH1a-SpaO抗血清凝集甲型副伤寒沙门菌的能力。采用小鼠感染模型了解rH1a-SpaO对甲型副伤寒沙门菌致死性感染的保护作用并与等量单一重组表达蛋白H1a（rH1a）及SpaO（rSpaO）比较。结果所构建的h1a-spaO融合基因与单一h1a或spaO基因核苷酸和氨基酸序列相似性均为100％。h1a-spaO融合基因原核表达系统能高效表达rH1a-SpaO。rH1a-SpaO能与rH1a或rSpaO抗血清结合，rH1a-SpaO抗血清也能识别rH1a和rSpaO并经H抗原凝集甲型副伤寒沙门菌。100μgrH1a-SpaO对甲型副伤寒沙门菌感染小鼠的免疫保护率（93．3％）明显高于等量rH1a（60．0％）及rSpaO（53．3％）（P＜0．05）。结论重组融合蛋白抗原rH1a-SpaO免疫保护作用较等量单一rH1a或rSpaO更强，可作为甲型副伤寒两价基因工程疫苗或伤寒/副伤寒荚膜多糖-蛋白结合疫苗的有效抗原。

Objective To construct a fusion gene （h1a-spaO） encoding H1a-SpaO protein of Sal-monella paratyphi A （ S.paratyphi A） and to express it in prokaryotic expression system , then to further ana-lyze the immunoprotective effects of the expressed protein rH 1a-SpaO.Methods The h1a-spaO fusion gene formed from separate h1a and spaO genes was amplified by PCR using flexible peptide sequence-containing linking primers and then sequenced after T-A cloning.A prokaryotic expression system for expressing h1a-spaO fusion gene was constructed by using the genetic engineering technique .The expressed protein rH1a-SpaO was examined by SDS-PAGE.The antigenicity and immunoreactivity of rH1a-SpaO protein were deter-mined by Western blot assay .The ability of rH1a-SpaO antiserum agglutinating S.paratyphi A strains was detected by micro-Widal′s test.The immunoprotective effects of rH 1a-SpaO against the lethal dose challenge of S.paratyphi A strains were analyzed in a mouse model and that were compared with those by using equal dose of individual recombinant protein H1a and SpaO （rH1a and rSpaO） as the immunogens, respectively. Results The h1a-spaO fusion gene was 100%identical with the individual h1a or spaO gene in nucleotide and amino acid sequences .The constructed prokaryotic expression system could express the recombinant pro-tein rH1a-SpaO with an advantage of high efficiency .rH1a-SpaO protein was able to react with rH 1a or rSpaO antiserum.Moreover, rH1a-SpaO antiserum also could efficiently recognize rH 1a and rSpaO as well as agglutinate Salmonella paratyphi A strains by binding with H-antigen.The immunoprotective rate （93.3%） in mice pre-immunized with 100 μg of rH1a-SpaO protein was significantly higher than that in those pre-immunized with equal dose of rH1a （60.0%） protein or rSpaO protein（53.3%） （P〈0.05）.Conclusion The recombinant fusion protein rH 1a-SpaO showed more stronger immunoprotective function than the individ-ual rH1a or rSpaO protein , which could be used as an effective antigen for the development of bi -valent para-typhoid A vaccine or typhoid/paratyphoid capsular polysaccharide-protein combined vaccine .