Molecular Mechanisms for the High Pathogenicity of 1918 Influenza Virus

描述（由申请人提供）：我们的长期目标是了解大流行性流感病毒的出现，例如1918年流感病毒，该病毒导致有记录以来最具破坏性的传染病爆发。特别是，我们提出了两个问题：（i）出现与1918年病毒相当的大流行毒株的可能性有多大？及（ii）1918年病毒的空前毒力的分子特徴为何？我们的研究发现，编码1918病毒样蛋白的禽流感病毒基因在自然界中仍然存在，这表明未来可能会出现类似1918大流行的病毒。因此，在目标1中，我们将评估出现类似1918年流感大流行病毒的风险。为了评估这种风险，我们已经产生了一种1918样禽流感病毒，其包含编码1918样蛋白的禽流感病毒片段。我们将把1918个病毒氨基酸导入该病毒，以确定对致病性至关重要的变化。在一个平行的方法中，我们已经产生了突变的1918病毒，其中一个基因在一个时间被替换为其最接近的鸟类亲属（如由蛋白质同源性确定）。将1918个氨基酸引入“禽”基因/蛋白质将揭示对1918病毒致病性至关重要的氨基酸。我们和其他人已经确定HA基因是1918年流感病毒前所未有的毒力的重要决定因素。HA蛋白在病毒生命周期中执行两个关键功能-受体结合以及病毒和内体膜的融合。目前，尚不清楚1918 HA蛋白是否在其受体结合特性和/或融合动力学方面与当代人类病毒不同，以及是否潜在的差异导致了1918病毒的高毒力。因此，在目标2中，我们将测试1918 HA蛋白是否与当代人类病毒的受体结合特性不同。这些特征可能受到HA糖基化模式的影响，促使我们测试非典型1918 HA糖基化模式对毒力的意义。此外，我们将表征1918 HA蛋白的融合动力学，特别强调在1918 HA蛋白中被认为影响融合的先前未识别的组氨酸补丁的表征。除HA基因外，病毒复制复合物已被确定为宿主范围和致病性的决定因素。我们的初步数据还表明1918年病毒复制复合物在1918年病毒毒力中的作用。然而，复制复合物的组分对增加的毒力和潜在机制（包括对宿主细胞反应的影响）的确切贡献目前尚不清楚，我们建议填补目标3中的知识空白。总的来说，这些研究旨在解决流感病毒研究中的两个关键问题-为什么1918年的病毒具有高致病性，以及出现另一种1918年类似病毒的风险是什么？公共卫生相关性：我们的长期目标是了解类似1918年大流行性流感病毒出现的可能性，以及导致1918年大流行性流感病毒前所未有的毒力的机制。这些知识将帮助我们为未来的流感大流行做好准备，并迅速识别具有大流行潜力的流感病毒株。

DESCRIPTION (provided by applicant): Our long-term goal is to understand the emergence of pandemic influenza viruses, such as the 1918 influenza virus that caused the most devastating outbreak of an infectious disease on record. In particular, we are asking two questions: (i) how likely is the emergence of a pandemic strain comparable to the 1918 virus?; and (ii) what are the molecular features that accounted for the unprecedented virulence of the 1918 virus? Our studies have revealed that avian influenza virus genes that encode 1918 virus-like proteins still exist in nature, suggesting that 1918-like pandemic viruses may emerge in the future. In Aim 1, we will therefore assess the risk for the emergence of 1918 virus-like pandemic influenza viruses. To assess this risk, we have generated a 1918-like avian influenza virus comprising avian influenza viral segments that encode 1918-like proteins. We will introduce 1918 viral amino acids into this virus to identify changes that are critical for pathogenicity. In a parallel approach, we have generated mutant 1918 viruses in which one gene at a time is replaced with its closest avian relative (as determined by protein homology). The introduction of 1918 amino acids into the 'avian' gene/protein will reveal amino acids that are critical for 1918 virus pathogenicity. We and others have identified the HA gene as an important determinant of the unprecedented virulence of the 1918 influenza virus. The HA protein carries out two critical functions in the viral life cycle - receptor-binding and fusion of the viral and endosomal membranes. Currently, it is not known if the 1918 HA protein differs in its receptor-binding properties and/or fusion kinetics from contemporary human viruses, and if potential differences contributed to the high virulence of the 1918 virus. In Aim 2, we will therefore test whether the 1918 HA protein differs from that of contemporary human viruses in its receptor-binding properties. These features may be affected by the HA glycosylation pattern, prompting us to test the significance of the atypical 1918 HA glycosylation pattern for virulence. In addition, we will characterize the fusion kinetics of the 1918 HA protein, with particular emphasis on the characterization of a previously unrecognized histidine patch in the 1918 HA protein that is thought to affect fusion. In addition to the HA gene, the viral replication complex has been identified as a determinant of host range and pathogenicity. Our preliminary data also suggest a role for the 1918 virus replication complex in the virulence of the 1918 virus. However, the exact contributions of the components of the replication complex to increased virulence and the underlying mechanisms (including effects on host cell responses) are currently unknown, a gap in knowledge that we propose to fill in Aim 3. Collectively, these studies are designed to address two critical questions in influenza virus research - why was the 1918 virus highly pathogenic, and what is the risk for emergence of another 1918-like virus? PUBLIC HEALTH RELEVANCE: Our long-term goal is to understand the likelihood of the emergence of 1918-like pandemic influenza viruses, and the mechanisms that accounted for the unprecedented virulence of the 1918 pandemic influenza virus. Such knowledge will help us to prepare for future influenza pandemics and to quickly recognize influenza virus strains with pandemic potential.