猪圆环病毒Ⅱ型ORF3基因缺失突变毒株对仔猪的致病性及免疫原性研究

Study on Pathogenicity and Immunogenicity of ORF3 Gene Deleted Mutational Strain of Porcine Circovirus Type 2 to Piglets

15头28～30日龄健康仔猪分成A、B、C3组（5头／组），分别肌注接种PCV2ORF3基因缺失突变毒株mPCV2-C、亲本毒株PCV2-CD以及生理盐水。用PCR-RFLP和PCR方法，分别从A组和B组屠宰仔猪的腹股沟淋巴结中特异性检测到mPCV2-C和PCV2-CDDNA，发现mPCV2-C能够在仔猪体内复制增殖。组织病理学结果表明；A组和B组腹股沟淋巴结、肝细胞及肺泡壁上皮细胞呈现病变，其中B组病变较严重，证实ORF3基因缺失未改变PCV2的组织嗜性。外周血T淋巴细胞亚群含量动态检测结果表明：与C组相比，A组、B组外周血CD3^＋、CD4^＋细胞百分含量降低，而A组CD8^＋细胞于免疫后第14天回升，高于B组和C组，表明ORF3基因缺失使病毒对T淋巴细胞亚群的影响有所减弱，并有诱导仔猪细胞免疫应答的趋势。上述结果提示ORF3缺失致使病毒的致病力有降低的趋势。PCV2抗体动态检测发现：mPCV2-C明显诱导了仔猪的体液免疫，具有良好的免疫原性。mPCV2-C可作为PCV2基因缺失疫苗候选毒株。

Fifteen healthy piglets aged 28 to 30 day-old were divided into three groups at random（5 piglets per group）, and were inoculated intramuscularly with mPCV2-C（ORF3 gene deleted mutational strain of PCV2）, PCV2-CD（parent strain） and physiologic saline, respectively. By using the methods of PCR-RFLP and PCR, the DNA of mPCV2-C and PCV2-CD were found in the inguinal lymph nodes of slaughtered piglets from group A and B respectively, which proved that the mPCV2-C could replicate and proliferate in piglet body. Observation on histopathology showed that some pathological changes were found in the inguinal lymph nodes, liver cells and alveolar wall epithelium in slaughtered piglets of group A and B, in which that of group B was more serious, the results proved that the ORF3 gene deletion didn＇t change the tissue tropism of PCV2. The dynamic determination of T lymphocyte subgroups in peripheral blood showed that, compared with group C, the percent of CD3- and CD4^＋T lymphocyte subgroups of group A and B decreased, and the CD8^＋ cell of group A returned high above that values of group B and C, which indicated that ORF3 gene deletion weakened the influences of PCV2 on T lymphocyte subgroups, and mPCV2-C demonstrated the tendency to induce cellular immunologic response in piglets. The results mentioned above also indicated the decrease tendency of pathogenicity of the virus with ORF3 gene deletion. The dynamic determination of antibody against PCV2 proved that mPCV2-C induced the humoral immunity in piglets obviously, and had good immunogenicity, mPCV2-C is a candidate strain for gene deletion vaccine against PCV2.