Department of Microbiology, Mount Sinai School of Medicine, 1 Gustave Levy Place, New York, NY 10029-6574, USA.
J Virol. 2010 May;84(9):4442-50. doi: 10.1128/JVI.02717-09. Epub 2010 Feb 24.
Unlike previous pandemic viruses, the 2009 H1N1 pandemic influenza virus does not code for the virulence factor PB1-F2. The genome of the 2009 H1N1 virus contains three stop codons preventing PB1-F2 expression; however, PB1-F2 production could occur following genetic mutation or reassortment. Thus, it is of great interest to understand the impact that expression of the PB1-F2 protein might have in the context of the 2009 pandemic influenza virus, A/California/04/2009 (Cal/09). We have addressed this question by generating two Cal/09 viruses with productive PB1-F2 open reading frames containing either an asparagine at position 66 of PB1-F2 (66N) or a serine at position 66 (66S): this N66S change has previously been shown to be associated with increased virulence in mice. We used these viruses to investigate the effect on virulence conferred by expression of the 66N or the 66S PB1-F2 protein in both in vitro and in vivo systems. Our results show enhanced replication of the 66S virus in A549 cells, while studies of BALB/c and DBA/2 mice and ferrets revealed no significant differences in symptoms of infection with wild-type Cal/09 versus the 66N or 66S virus variant. Also, coinfection of mice with Streptococcus pneumoniae and the different viruses (recombinant wild-type [rWT] Cal/09 and the 66N and 66S viruses) did not result in significant differences in mortality. Mice infected with either PB1-F2-expressing virus did demonstrate altered protein levels of proinflammatory cytokines; differences were observed to be greater in infection caused by the 66S virus. In summary, our study demonstrates that PB1-F2 expression by the Cal/09 virus modulates the immune response to infection while having a minimal effect on virus virulence in two mammalian models.
与以往的大流行病毒不同，2009 年 H1N1 大流行流感病毒不编码毒力因子 PB1-F2。2009 年 H1N1 病毒的基因组包含三个终止密码子，阻止 PB1-F2 的表达；然而，PB1-F2 的产生可能是由于遗传突变或重配。因此，了解 PB1-F2 蛋白的表达可能对 2009 年大流行流感病毒 A/加利福尼亚/04/2009（Cal/09）产生的影响非常重要。我们通过生成两种具有生产性 PB1-F2 开放阅读框的 Cal/09 病毒来解决这个问题，这些开放阅读框包含 PB1-F2 第 66 位的天冬酰胺（66N）或丝氨酸（66S）：先前的研究表明，这种 N66S 变化与在小鼠中增加的毒力有关。我们使用这些病毒在体外和体内系统中研究表达 66N 或 66S PB1-F2 蛋白对毒力的影响。我们的结果显示，66S 病毒在 A549 细胞中的复制增强，而对 BALB/c 和 DBA/2 小鼠和雪貂的研究表明，与野生型 Cal/09 相比，感染 66N 或 66S 病毒变体的症状没有显著差异。此外，用肺炎链球菌和不同病毒（重组野生型[ rWT ] Cal/09 和 66N 和 66S 病毒）对小鼠进行共感染不会导致死亡率有显著差异。感染表达 PB1-F2 的病毒的小鼠确实表现出促炎细胞因子的蛋白水平改变；观察到由 66S 病毒引起的感染差异更大。总之，我们的研究表明，Cal/09 病毒的 PB1-F2 表达调节了感染引起的免疫反应，而在两种哺乳动物模型中对病毒毒力的影响最小。
