BPIV3 NP蛋白的原核表达及其对BPIV3灭活疫苗免疫增强作用的研究

Prokaryotic Expression of BPIV3 NP Protein and Its Immunoenhancing Effect on the BPIV3 Inactivated Vaccine

【目的】验证牛副流感病毒3型(Bovine parainfluenza virus type 3,BPIV3)NP蛋白对BPIV3灭活疫苗的免疫效果是否有增强作用。【方法】利用生物信息学软件对NP基因编码的蛋白进行抗原性分析,筛选出抗原性区域,采用PCR方法扩增BPIV3截短的NP基因序列,连接至pET-32a(+)质粒上,通过大肠杆菌原核表达系统和Ni亲和层析的方法获得了较高纯度的BPIV3 NP蛋白,经Western blotting验证其反应原性。将BPIV3用0.3%甲醛灭活后与弗氏佐剂1∶1混合制备灭活疫苗。8只新西兰白兔随机分为4组:灭活疫苗组、NP蛋白组、灭活疫苗和NP蛋白混合组及对照组,每组2只。免疫前及免疫后每7 d采集血液分离血清,采用间接ELISA方法和病毒中和试验测定并比较4组新西兰白兔特异性抗体和中和抗体的水平。【结果】经DNAStar分析,NP蛋白第193-368位氨基酸处的平均抗原指数在0.4~1.7之间,亲水指数为0~1.5,证明该区域抗原性和亲水性较强;通过PCR扩增得到NP基因,并构建重组表达载体,通过基因测序证明该重组表达载体与预期结果一致;SDS-PAGE结果显示,NP蛋白表达量较高,蛋白分子质量为50 ku且以包涵体形式表达;Western blotting结果表明,所表达的蛋白具有较强的反应原性;ELISA结果显示,在免疫后28 d,对照组的特异性抗体效价为0,灭活疫苗组、NP蛋白组及灭活疫苗和NP蛋白混合组的特异性抗体效价分别达到1∶2^(11)、1∶2^(17)和1∶2^(18)。病毒中和试验结果显示,在免疫后28 d,对照组中和抗体效价为0,灭活疫苗组、NP蛋白组及灭活疫苗和NP蛋白混合组的中和抗体效价分别为1∶2^(3.32)、1∶2^(4.48)和1∶2^(4.98)。【结论】BPIV3 NP蛋白可增强BPIV3灭活疫苗的免疫效果,在灭活疫苗中加入NP蛋白可作为BPIV3灭活疫苗的新型接种方法。

【Objective】This study was aimed to verify whether the NP protein of Bovine parainfluenza virus type 3(BPIV3)could enhance the immune effect of BPIV3 inactivated vaccine【Method】The antigenicity of the protein encoded by NP gene was analyzed by bioinformatics softwares,and the antigenic region was screened.The truncated NP gene sequence of BPIV3 was amplified by PCR and connected to pET-32 a(+)plasmid.Then the high-purity BPIV3 NP protein was obtained by E.coli prokaryotic expression system and Ni affinity chromatography.It was confirmed by Western blotting.BPIV3 was inactivated with 0.3%formaldehyde and mixed with Freund’s adjuvant 1∶1 to prepare inactivated vaccine.Eight New Zealand White rabbits were randomly divided into four groups with two rabbits in each group,including inactivated vaccine group,NP protein group,inactivated vaccine and NP protein mixed group and control group.Blood samples were collected before and every 7 days after immunization.The levels of specific antibodies and neutralizing antibodies in New Zealand White rabbits of the four groups were measured and compared by indirect ELISA and virus neutralization test.【Result】DNAStar analysis showed that the average antigen index of amino acid region 193-368 of NP protein was 0.4-1.7,and the hydrophilic index was 0-1.5,which proved that this region had strong antigenicity and hydrophilicity.The NP gene was amplified by PCR and the recombinant expression vector was constructed.Gene sequencing showed that the recombinant expression vector was consistent with the expected results.The results of SDS-PAGE showed that NP protein was highly expressed with a molecular weight of 50 ku and expressed in the form of inclusion body.Western blotting showed that the expressed protein had strong reactivity.The results of ELISA showed that 28 days after immunization,the specific antibody titer of the control group was 0,and the specific antibody titers of inactivated vaccine group,NP protein group and inactivated vaccine and NP protein mixed group reached 1∶2^(11),1∶2^(17) and 1∶2^(18),respectively.The results of virus neutralization test showed that 28 days after immunization,the neutralizing antibody titer of the control group was 0,and the neutralizing antibody titers of inactivated vaccine group,NP protein group and inactivated vaccine and NP protein mixed group were 1∶2^(3.32),1∶2^(4.48) and 1∶2^(4.98),respectively.【Conclusion】BPIV3 NP protein could enhance the immune effect of BPIV3 inactivated vaccine.Adding NP protein to the inactivated vaccine could be used as a new vaccination method of BPIV3 inactivated vaccine.