重新评价G-480位点变异对Ⅰ型脊髓灰质炎疫苗病毒神经毒力的影响

在对分离于中国贵州省的9株Ⅰ型循环的疫苗衍生脊髓灰质炎病毒（cVDPVs）进行全基因组核苷酸序列分析后，发现已知最重要的决定病毒神经毒力的位点G-480和U-525并没有发生回复野生型突变；另外一些已知的神经毒力决定位点，如A-2438、A-2795、C-6203和G-7441等均已经发生了回复野生型突变。根据核苷酸序列的不同，从9株Ⅰ型cVDPVs毒株中选取5株病毒感染转人脊髓灰质炎病毒受体基因的小鼠进行神经毒力实验，发现它们的神经毒力都有所升高，其中CHN8184株和CHN8229-1．1株的神经毒力已经十分接近P1／Mahoney株，CHN8229-1．1株、CHN8229-2株和CHN8229-3株神经毒力依次递减，但仍处于较高水平，在它们的全基因组中分别只有7个和2个核苷酸的差异，而毒力却相差很多，提示有新的未鉴别的神经毒力决定位点的存在。对这些毒株5′非编码区（5′NCR）的第Ⅴ结构域进行二级结构预测，发现它们的二级结构很稳定。在G-480位点没有发生回复突变的情况下，部分毒株的神经毒力已经非常接近P1／Mahoney的水平，提示先前的研究中关于G-480突变对Ⅰ型脊髓灰质炎病毒神经毒力的作用可能被估计过高，G-480位点不是唯一重要的神经毒力决定位点，可能多个核苷酸联合突变才能达到减毒的效果。要真正全面了解P1／Sabin株的减毒机制，还需要进行更加深入的研究。

Reevaluate the Effect of G-480 Point Mutation that Determines the Neurovirulence of Type Ⅰ Vaccine Polioviruses

Whole genome sequencing of 9 type I circulating vaccine-derived polioviruses (cVDPVs) isolated in Guizhou Province in China revealed that reverse mutations did not occur in G-480 and U-525 which are known as the most important neurovirulence determinate sites, while other known neurovirulence determinate sites such as A-2438, A-2795, C-6203 and G-7441 did revert to Mahoney type. 5 type I cVDPVs were selected for neurovirulence test on PVR-Tg21 transgenic mice which express human poliovirus receptor gene based on their different nucleotide sequences, they all showed higher neurovirulence than P1/Sabin strain, and the neurovirulence of CHN8184 and CHN8229-1. 1 were comparable to that of wild type P1/Mahoney. The neurovirulence of CHN8229-1.1, CHN8229-2 and CHN8229-3 presented a trend of decreasing, but still laid in high level. There were 7 nucleotide mutations between CHN8229-1.1 and CHN8229-2, and only 2 between CHN8229-2 and CHN8229-3 in their whole genomes, but the neurovirulence among them were relatively different, showing that there must be some unknown neurovirulence determinate sites among these mutations. Computer predicted RNA secondary structure of stem-loop V of the poliovirus 5' NCR of Guizhou type I cVDPVs was relatively stable. In the situation that no reverse mutation occurred in G-480, some type I cVDPVs already showed high neurovirulence nearly equal to P1/Mahoney, it meant that the effect of G-480 point mutation that determined neurovirulence of P1/Sabin strain has been overestimated, G-480 was not the only important site to determine neurovirulence in P1/Sabin strain, others also may play the very important role. More details are needed to elucidate the mechanism of attenuation in type I polioviruses.