中文摘要：

为研究猪繁殖与呼吸综合征病毒（PRRSV）在猪干扰素-β（swIFN-β）免疫压力下的分子变异情况，本研究将高致病性PRRSVJXAl株在添加适量swlFN-β的Marc-145细胞中连续传20代后，获得PRRSV-A1βf20株及正常传代对照株PRRSV-A1f20。序列分析结果显示：PRRSV-A1βf20与PRRSV-A1f20在NSP2、ORF3、ORF5和ORF6等基因中累计分别出现43个和14个核苷酸突变，并分别导致24个和6个氨基酸改变，有义突变与沉默突变比值（NS／S1分别为3和0．625，两者的氨基酸突变速率比为400％。PRRSV—A1βf20株的ORF5、NSP2、ORF3和ORF6的氨基酸突变率为4．5％、3．8％、2．3％和0．57％，NS／S比值为7、3．3、2和1，远高于PRRSV—Alf20株氨基酸突变率和NS／S比值。上述结果表明：在swIFN-β存在时，PRRSV变异显著加快，呈现明显的压力选择性交变；swIFN-β的选择压力对PRRSV的ORF5基因变异影响最大，NSP2次之，属于免疫突变正向效应，而对ORF3基因影响最小，对ORF6几乎无影响。推测PRRSV的NSP2和ORF5基因可能在PRRSV对swIFN—β的免疫逃逸中起重要作用。本研究首次报道了PRRSV在swlFNβ免疫压力下遗传变异加快的正向效应。

英文摘要：

In order to investigate the molecular variation of porcine reproductive and respiratory syndrome virus （PRRSV） treated with sw FN-β, PRRSV-A1βf20 was obtained by serial passage of the highly pathogenic PRRSV JXA1 adding swlFN-β in Marc-145 cell culturing, with the untreated PRRSV-Alf20 as control. Sequence analysis revealed that 43 and 14 nucleotide mutations were identified, also 24 and 16 amino acid were changed in NSP2, ORF3, ORF5, ORF6 genes of PRRSV-Alβf20 and PRRSV-Alf20, respectively. Amino acid mutations ratio was 400% between PRRSV-A1βf20 and PRRSV-Alf20, sense mutation/silent mutation ratio （NS/S） were 3 and 0.625, respectively. Amino acid mutations ratio and NS/S ratio of PRRSV-A1βf20 in ORF5, NSP2, ORF3, ORF6 were significantly greater than PRRSV-Alf20, which were 4.5%, 3.8%, 2.3%, 0.57% and 7, 3.3, 2, 1, respectively. These results indicated that PRRSV variation was remarkable accelerated and showed selective mutation in the presence of swlFN-β; selection pressure of swlFN-β was the most influence on ORF5, NSP2 took second place, while it had the least influence on ORF3 and had almost no effect on ORF6. Therefore, we speculated that NSP2 and ORF5 might play an important role in PRRSV toward immune escape of swlFN-β.