中文摘要：

马传染性贫血病毒（EIAV）减毒疫苗是世界首例慢病毒疫苗,但其作用机理尚不明了.研究发现,EIAV疫苗株EIAVFDDV12的跨膜蛋白gp45在马体内发生高频率261W位点翻译终止突变,使该蛋白质C端出现154个氨基酸的截短.为了探讨该截短对EIAV疫苗株生物学特性的作用,以EIAV弱毒疫苗株感染性克隆为骨干,构建了gp45截短型感染性病毒株,检测该截短突变对EIAV疫苗株在体外培养的马外周血单核细胞由来的巨噬细胞（MDM）、驴MDM和驴胎皮细胞（FDD）中的复制.实验结果表明,gp45截短型毒株在马和驴MDM中复制能力比未截短型毒株显著降低（P〈0.01）,特别是在马MDM中此差异更明显.相反,截短型毒株在FDD中的复制能力则显著高于未截短型毒株（P〈0.01）.此外,结果显示gp45截短型毒株在马MDM中的低水平复制降低了EIAV对其靶细胞诱导的凋亡.以上结果提示,EIAV疫苗的gp45截短型毒株是适应在体外FDD细胞中传代致弱的变异,该变异导致疫苗株在EIAV体内主要靶细胞巨噬细胞中复制能力的降低,导致毒力进一步减弱.

英文摘要：

Equine infectious anemia virus （EIAV） vaccine is the first successfully applied lentiviral vaccine, but its mechanism on inducing protective immunity is not clear. Previous studies found that the EIAV vaccine strain EIAVFDDV12 transmembrane protein （gp45） had a high-frequent translational terminating mutation at the site of 261W, resulting in a truncation of 154 amino acid residues at the C-terminus. To explore the biological meaning of the gp45 truncation, a gp45-truncated molecular clone was constructed by using an infectious clone of EIAVFDDV12 as the backbone. Replications features of the gp45-truncated EIAV and its prototype virus were analyzed and compared in cultivated monocyte-derived macrophages （MDM） of equine and donkey and fetal donkey dermal cells （FDD）. Results showed that the replication capacity of the gp45-truncated EIAV in equine and donkey MDMs was significantly decreased compared to the untruncated gp45 EIAV（P 0.01）, especially in the horse macrophages. In contrast, the truncated EIAV replicated significantly faster than the untruncated EIAV in FDD cells （P 0.01）. In addition, the reduced replication of the gp45-truncated EIAV in equine MDM led to a significant decline of cytotoxicity of the host cells when compared with the gp45 untruncated EIAV （P 0.05）. These results suggest that the truncation of the 154-residue C-terminus of the EIAV gp45 glycoprotein was an adaptation to the attenuation of the EIAV vaccine strain in FDD cells. This truncated mutation reduces the replication of the vaccine strain in macrophages, the primary in vivo target cell of EIAV, which leads to a further attenuation of the vaccine.