Necessity of adaptation of RNA viruses in host switching events between taxonomically distant reservoir animals

大多数新出现的传染病是由人畜共患的RNA病毒引起的，通常由蝙蝠、啮齿动物和鸟类传播。它们的高突变率允许快速适应新物种，增加了人畜共患宿主转变的风险。宿主防御机制，如先天免疫反应，在高等脊椎动物中是保守的，是病毒必须克服的主要障碍。作为先天免疫反应的一部分，干扰素系统是最早也是最有效的抗病毒防御机制之一，病毒已经进化出有效的对策(干扰素拮抗剂)来抑制干扰素的诱导和信号传递。因此，可以假设干扰素系统是决定病毒宿主转换事件的命运的。拟议项目的目的是分析病毒在宿主转换期间适应的必要性是否在定量尺度上与感兴趣宿主之间的系统发育距离相关。我们将重点研究病毒对不同宿主物种特异性干扰素诱导途径的拮抗能力。为此，我们想要量化已知的六种病毒(SARS冠状病毒、埃博拉病毒、尼帕病毒、狂犬病病毒、汉塔病毒和甲型流感病毒)的病毒抗干扰素蛋白在12种不同哺乳动物/鸟类的细胞培养中的活性。这将通过在各自的细胞培养中过度表达拮抗剂，然后刺激干扰素的诱导来实现。预测的自然宿主的细胞培养将作为参考。干扰素mRNA的表达将通过物种特异性实时RT-PCRS进行检测。干扰素的分泌将通过已建立的基于水泡性口炎病毒的已建立的校准泛物种生物测定来确定。体外干扰素实验的定量结果将直接与基于不同基因簇的宿主间的专利距离相关。后者应在由ML-和贝叶斯方法计算的单个和串联的基因树上表达。由于我们对先天免疫反应感兴趣，我们还将包括与干扰素反应相关的基因和启动子。作为一个长期目标，我们希望识别病毒家族或宿主间距离特定的模式，这将有助于在检测到新的水库传播病毒时立即进行风险评估。

The majority of emerging infectious diseases are caused by zoonotic RNA viruses often transmitted by bats, rodents and birds. Their high mutation rate allows fast adaptation to novel species increasing the risk for zoonotic host transitions. Host defense mechanisms like the innate immune response are conserved among higher vertebrates and represent a major obstacle that viruses have to overcome. The interferon (IFN) system as part of the innate immune response is among the first and most effective antiviral defense mechanisms and viruses have evolved efficient countermeasures (IFN antagonists) to inhibit the induction and signaling of IFN. It can thus be assumed that the IFN system is fate-determining for viral host switching events.The aim of the proposed project is to analyze if the necessity for viruses to adapt during host transition correlates on a quantitative scale with the phylogenetic distance between hosts of interest. We will focus our study on the ability of viruses to antagonize the species-specific IFN induction pathway of different hosts. To this end we want to quantify the activity of known viral anti- IFN proteins of six selected viruses (SARS-Coronavirus, Ebola-, Nipah-, Rabies-, Hanta- and Influenza A virus) in cell cultures from 12 different mammalian/avian species. This will be done by overexpressing the antagonists in the respective cell cultures followed by stimulation of the IFN induction. Cell cultures from the predicted natural hosts will be used as reference. The IFN mRNA expression will be measured by species-specific real-time RT-PCRs. The IFN secretion will be determined by an established calibrated pan-species vesicular stomatitis virus-based bioassay. Quantitative outcomes of the in-vitro IFN experiments will be directly correlated with inter-host patristic distances based on different gene clusters. The latter shall be expressed along single and concatenated gene trees calculated by ML- and Bayesian methods. Since we are interested in innate immune responses we will also include genes and promoters specifically involved in the IFN response.As a long-term goal we want to identify virus family- or inter-host distance-specific patterns that will facilitate risk assessment of novel reservoir-borne viruses immediately as they are being detected.