In this study, we demonstrate a novel mechanism for hemagglutinin (HA) activation in a naturally occurring H7N6 avian influenza A virus strain, A/mallard duck/Korea/6L/2007 (A/Mdk/6L/07). This novel mechanism allows for systemic infection of chickens, ducks, and mice, and A/Mdk/6L/07 can replicate in vitro without exogenous trypsin and exhibits broad tissue tropism in animals despite the presence of a monobasic HA cleavage motif (PEIPKGR/G). The trypsin-independent growth phenotype requires the N6 neuraminidase and the specific recognition of glycine at the P2 position of the HA cleavage motif by a thrombin-like protease. Correspondingly, viral growth is significantly attenuated by the addition of a thrombin-like protease inhibitor (argatroban). These data provide evidence for a previously unrecognized virus replication mechanism and support the hypothesis that thrombin-mediated HA cleavage is an important virulence marker and potential therapeutic target for H7 influenza viruses.IMPORTANCE The identification of virulence markers in influenza viruses underpins risk assessment programs and the development of novel therapeutics. The cleavage of the influenza virus HA is a required step in the viral life cycle, and phenotypic differences in viruses can be caused by changes in this process. Here, we describe a novel mechanism for HA cleavage in an H7N6 influenza virus isolated from a mallard duck. The mechanism requires the N6 protein and full activity of thrombin-like proteases and allows the virus to cause systemic infection in chickens, ducks, and mice. The thrombin-mediated cleavage of HA is thus a novel virulence determinant of avian influenza viruses.

中文翻译：

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一种新型的神经氨酸酶依赖性血凝素裂解机制使H7N6禽流感病毒得以系统传播。

在这项研究中，我们证明了天然存在的H7N6禽流感A病毒株A /野鸭/韩国/ 6L / 2007（A / Mdk / 6L / 07）中血凝素（HA）激活的新机制。这种新颖的机制可对鸡，鸭和小鼠进行全身感染，尽管存在一元HA裂解基序（PEIPKGR / G），A / Mdk / 6L / 07仍可在没有外源胰蛋白酶的情况下在体外复制，并在动物体内表现出广泛的组织嗜性。 ）。胰蛋白酶非依赖性生长表型需要N6神经氨酸酶和凝血酶样蛋白酶在HA切割基序的P2位置对甘氨酸的特异性识别。相应地，通过添加凝血酶样蛋白酶抑制剂（argatroban），病毒的生长显着减弱。这些数据为以前无法​​识别的病毒复制机制提供了证据，并支持了以下假设：凝血酶介导的HA裂解是H7流感病毒的重要毒力标志物和潜在治疗靶标。新疗法的发展。流感病毒HA的切割是病毒生命周期中的必要步骤，病毒的表型差异可能是由该过程的变化引起的。在这里，我们描述了从野鸭中分离出的H7N6流感病毒中HA裂解的新机制。该机制需要N6蛋白和凝血酶样蛋白酶的完全活性，并允许病毒在鸡，鸭和小鼠中引起全身感染。