Department of Viroscience, Erasmus MC, Rotterdam, The Netherlands.
Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, USA.
J Virol. 2018 Feb 12;92(5). doi: 10.1128/JVI.02063-17. Print 2018 Mar 1.
Exchange of gene segments through reassortment is a major feature of influenza A virus evolution and frequently contributes to the emergence of novel epidemic, pandemic, and zoonotic strains. It has long been evident that viral diversification through reassortment is constrained by genetic incompatibility between divergent parental viruses. In contrast, the role of virus-extrinsic factors in determining the likelihood of reassortment has remained unclear. To evaluate the impact of such factors in the absence of confounding effects of segment mismatch, we previously reported an approach in which reassortment between wild-type (wt) and genetically tagged variant (var) viruses of the same strain is measured. Here, using wt/var systems in the A/Netherlands/602/2009 (pH1N1) and A/Panama/2007/99 (H3N2) strain backgrounds, we tested whether inoculation of parental viruses into distinct sites within the respiratory tract limits their reassortment. Using a ferret () model, either matched parental viruses were coinoculated intranasally or one virus was instilled intranasally whereas the second was instilled intratracheally. Dual intranasal inoculation resulted in robust reassortment for wt/var viruses of both strain backgrounds. In contrast, when infections were initiated simultaneously at distinct sites, strong compartmentalization of viral replication was observed and minimal reassortment was detected. The observed lack of viral spread between upper and lower respiratory tract tissues may be attributable to localized exclusion of superinfection within the host, mediated by innate immune responses. Our findings indicate that dual infections in nature are more likely to result in reassortment if viruses are seeded into similar anatomical locations and have matched tissue tropisms. Genetic exchange between influenza A viruses (IAVs) through reassortment can facilitate the emergence of antigenically drifted seasonal strains and plays a prominent role in the development of pandemics. Typical human influenza infections are concentrated in the upper respiratory tract; however, lower respiratory tract (LRT) infection is an important feature of severe cases, which are more common in the very young, the elderly, and individuals with underlying conditions. In addition to host factors, viral characteristics and mode of transmission can also increase the likelihood of LRT infection: certain zoonotic IAVs are thought to favor the LRT, and transmission via small droplets allows direct seeding into lower respiratory tract tissues. To gauge the likelihood of reassortment in coinfected hosts, we assessed the extent to which initiation of infection at distinct respiratory tract sites impacts reassortment frequency. Our results reveal that spatially distinct inoculations result in anatomical compartmentalization of infection, which in turn strongly limits reassortment.
通过重配交换基因片段是甲型流感病毒进化的一个主要特征，经常导致新的流行、大流行和人畜共患病株的出现。长期以来，人们已经明显认识到，通过重配实现病毒多样化受到不同亲代病毒之间遗传不相容性的限制。相比之下，病毒外在因素在决定重配可能性方面的作用仍不清楚。为了在没有片段不匹配的混杂效应的情况下评估这些因素的影响，我们之前报告了一种方法，即在同一株的野生型（wt）和遗传标记的变异（var）病毒之间进行重配。在这里，我们使用 A/Netherlands/602/2009（pH1N1）和 A/Panama/2007/99（H3N2）株的 wt/var 系统，测试了将亲代病毒接种到呼吸道的不同部位是否会限制它们的重配。使用雪貂（）模型，将匹配的亲代病毒经鼻腔同时接种或仅经鼻腔接种一种病毒，而另一种病毒经气管内接种。两种病毒经鼻腔同时接种导致两种株背景的 wt/var 病毒的重配非常强烈。相比之下，当感染同时在不同部位开始时，观察到病毒复制的强烈分隔，并且检测到最小的重配。在上呼吸道和下呼吸道组织之间观察到的病毒传播缺乏可能归因于宿主中局部排除超感染，这是由先天免疫反应介导的。我们的发现表明，如果病毒接种到类似的解剖位置并且具有匹配的组织嗜性，那么在自然界中双重感染更有可能导致重配。甲型流感病毒（IAV）之间通过重配进行的基因交换可以促进抗原漂移的季节性株的出现，并在大流行的发展中发挥重要作用。典型的人类流感感染集中在上呼吸道；然而，下呼吸道（LRT）感染是严重病例的一个重要特征，在非常年幼、年老和有基础疾病的人中更为常见。除了宿主因素外，病毒特征和传播方式也会增加 LRT 感染的可能性：某些人畜共患 IAV 被认为有利于 LRT，通过小飞沫传播可以直接将病毒种子播种到下呼吸道组织中。为了评估在合并感染宿主中重配的可能性，我们评估了在不同呼吸道部位开始感染对重配频率的影响程度。我们的结果表明，空间上的不同接种导致感染的解剖学分隔，这反过来又强烈限制了重配。
