Ren Jing-Qiang, Sun Wen-Chao, Lu Hui-Jun, Wen Shu-Bo, Jing Jie, Yan Fu-Long, Liu Hao, Liu Cun-Xia, Xiao Peng-Peng, Chen Xing, Du Shou-Wen, Du Rui, Jin Ning-Yi
Institute of Military Veterinary, Key Laboratory of Jilin Province for Zoonosis Prevention and Control, Academy of Military Medical Sciences, Changchun 130122, China.
BMC Vet Res. 2014 Jun 10;10:128. doi: 10.1186/1746-6148-10-128.
The European (EU) genotype of porcine reproductive and respiratory syndrome virus (Genotype-I PRRSV) has recently emerged in China. The coexistence of Genotype-I and -II PRRSV strains could cause seriously affect PRRSV diagnosis and management. Current vaccines are not able to protect against PRRSV infection completely and have inherent drawbacks. Thus, genetically engineered vaccines, including DNA vaccine and live vector engineered vaccines, have been developed. This study aimed to determine the enhanced immune responses of mice inoculated with a DNA vaccine coexpressing GP3 and GP5 of a Genotype-I PRRSV.
To evaluate the immunogenicity of GP3 and GP5 proteins from European-type PRRSV, three DNA vaccines, pVAX1-EU-ORF3-ORF5, pVAX1-EU-ORF3 and pVAX1-EU-ORF5, were constructed, which were based on a Genotype-I LV strain (GenBank ID: M96262). BALB/c mice were immunized with the DNA vaccines; delivered in the form of chitosan-DNA nanoparticles. To increase the efficiency of the vaccine, Quil A (Quillaja) was used as an adjuvant. GP3 and GP5-specific antibodies, neutralizing antibodies and cytokines (IL-2, IL-4, IL-10 and IFN gamma) from the immunized mice sera, and other immune parameters, were examined, including T-cell proliferation responses and subgroups of spleen T-lymphocytes. The results showed that ORF3 and ORF5 proteins of Genotype-I PRRSV induced GP3 and GP5-specific antibodies that could neutralize the virus. The levels of Cytokines IL-2, IL-4, IL-10, and IFN-γ of the experimental groups were significantly higher than those of control groups after booster vaccination (P < 0.05). The production of CD3+CD4+ and CD3+CD8+ T lymphocyte was also induced. T lymphocyte proliferation assays showed that the PRRSV LV strain virus could stimulate the proliferation of T lymphocytes in mice in the experimental group.
Using Quil A as adjuvant, Genotype-I PRRSV GP3 and GP5 proteins produced good immunogenicity and reactivity. More importantly, better PRRSV-specific neutralizing antibody titers and cell-mediated immune responses were observed in mice immunized with the DNA vaccine co-expressing GP3 and GP5 proteins than in mice immunized with a DNA vaccine expressing either protein singly. The results of this study demonstrated that co-immunization with GP3 and GP5 produced a better immune response in mice.
猪繁殖与呼吸综合征病毒的欧洲（EU）基因型（基因I型PRRSV）最近在中国出现。基因I型和II型PRRSV毒株的共存可能会严重影响PRRSV的诊断和防控。目前的疫苗不能完全预防PRRSV感染，且存在固有缺陷。因此，已经开发了包括DNA疫苗和活载体工程疫苗在内的基因工程疫苗。本研究旨在确定接种共表达基因I型PRRSV的GP3和GP5的DNA疫苗的小鼠的增强免疫反应。
为了评估欧洲型PRRSV的GP3和GP5蛋白的免疫原性，构建了三种基于基因I型LV毒株（GenBank ID：M96262）的DNA疫苗，即pVAX1-EU-ORF3-ORF5、pVAX1-EU-ORF3和pVAX1-EU-ORF5。BALB/c小鼠用这些DNA疫苗进行免疫；疫苗以壳聚糖-DNA纳米颗粒的形式递送。为了提高疫苗效率，使用了Quil A（皂树）作为佐剂。检测了免疫小鼠血清中的GP3和GP5特异性抗体、中和抗体和细胞因子（IL-2、IL-4、IL-10和IFN-γ），以及其他免疫参数，包括T细胞增殖反应和脾脏T淋巴细胞亚群。结果表明，基因I型PRRSV的ORF3和ORF5蛋白诱导产生了能中和病毒的GP3和GP5特异性抗体。加强免疫后，实验组的细胞因子IL-2、IL-4、IL-10和IFN-γ水平显著高于对照组（P<0.05）。还诱导了CD3+CD4+和CD3+CD8+T淋巴细胞的产生。T淋巴细胞增殖试验表明，PRRSV LV毒株病毒能刺激实验组小鼠T淋巴细胞的增殖。
以Quil A作为佐剂，基因I型PRRSV的GP3和GP5蛋白具有良好的免疫原性和反应性。更重要的是，与单独表达一种蛋白的DNA疫苗免疫的小鼠相比，用共表达GP3和GP5蛋白的DNA疫苗免疫的小鼠观察到更好的PRRSV特异性中和抗体滴度和细胞介导的免疫反应。本研究结果表明，GP3和GP5共同免疫在小鼠中产生了更好的免疫反应。
