Gu Jinyuan, Yan Yayao, Zeng Zixiong, Liu Dong, Hu Jiao, Hu Shunlin, Wang Xiaoquan, Gu Min, Liu Xiufan
Animal Infectious Disease Laboratory, College of Veterinary Medicine, Yangzhou University, Yangzhou, PR China; Shandong Engineering Research Center of Swine Health Data and Intelligent Monitoring, Dezhou University, Dezhou, PR China.
Animal Infectious Disease Laboratory, College of Veterinary Medicine, Yangzhou University, Yangzhou, PR China.
Poult Sci. 2025 Feb;104(2):104832. doi: 10.1016/j.psj.2025.104832. Epub 2025 Jan 18.
H7N9 avian influenza virus (AIV) first emerged in February 2013 in China, and early isolates were all low pathogenic (LP). After circulation for a few years in live poultry markets of China, LP H7N9 AIVs evolved into a highly pathogenic (HP) form in late 2016. Deduced amino acid sequence analysis of hemagglutinin (HA) gene revealed that all HP H7N9 AIVs have obtained four-amino-acid insertion at position 339-342 (H7 numbering), making the cleavage site from a monobasic motif (LP AIVs) to a polybasic form (HP AIVs). Notably, the polybasic cleavage site motifs are diversified, of which PEVPKRKRTAR↓GLF motif is prevalent. To elucidate the reasons accounting for its dominance, recombinant H7N9 virus carrying PEVPKRKRTAR↓GLF (rJT157-2) motif was generated based on LP H7N9 virus A/chicken/Eastern China/JT157/2016 (JT157). Besides, another two viruses containing PEVPKGKRTAR↓GLF (rJT157-1) and PEIPKRKRTAR↓GLF (rJT157-3) cleavage site motifs were also constructed as comparisons. We found that rJT157-2 showed better biological characterizations in vitro including replication kinetics, plaque size, thermal and acid stability. In addition, animal experiments demonstrated that rJT157-2 was more pathogenic to both chickens and mice with higher virus titers and induced more severe changes in the lungs. These results suggested that HP H7N9 viruses carrying PEVPKRKRTAR↓GLF motif in the HA cleavage site were most likely adaptive mutants during the evolution of H7N9 AIVs.
H7N9禽流感病毒（AIV）于2013年2月首次在中国出现，早期分离株均为低致病性（LP）。在中国活禽市场传播数年之后，LP H7N9 AIV于2016年末演变成高致病性（HP）形式。血凝素（HA）基因的推导氨基酸序列分析显示，所有HP H7N9 AIV在339-342位（H7编号）均获得了四个氨基酸的插入，使裂解位点从单碱性基序（LP AIV）变为多碱性形式（HP AIV）。值得注意的是，多碱性裂解位点基序具有多样性，其中PEVPKRKRTAR↓GLF基序最为普遍。为阐明其占主导地位的原因，基于LP H7N9病毒A/鸡/中国东部/JT157/2016（JT157）构建了携带PEVPKRKRTAR↓GLF（rJT157-2）基序的重组H7N9病毒。此外，还构建了另外两种含有PEVPKGKRTAR↓GLF（rJT157-1）和PEIPKRKRTAR↓GLF（rJT157-3）裂解位点基序的病毒作为对照。我们发现，rJT157-2在体外表现出更好的生物学特性，包括复制动力学、蚀斑大小、热稳定性和酸稳定性。此外，动物实验表明，rJT157-2对鸡和小鼠的致病性更强，病毒滴度更高，并在肺部引起更严重的变化。这些结果表明，HA裂解位点携带PEVPKRKRTAR↓GLF基序的HP H7N9病毒很可能是H7N9 AIVs进化过程中的适应性突变体。
