Molecular biology and spill-over potential of bat influenza A-like viruses

最近，在中美洲和南美洲蝙蝠物种中发现了两种新的流感亚型，暂时命名为H17N10和H18N11，这对先前对甲型流感病毒（IAV）宿主范围和多样性的理解提出了挑战。这两种亚型的表面糖蛋白分别缺乏常规血凝素（HA）和神经氨酸酶（NA）蛋白的典型受体结合和受体破坏活性。从感染蝙蝠中分离病毒或产生重组病毒失败，阻碍了对其致病性和人畜共患潜力的研究。我们可以证明蝙蝠嵌合病毒编码传统IAV的HA和NA不能与传统IAV重配。在第一个资助期，我们确定了这种重配不相容的潜在机制，这是由蝙蝠IAV核蛋白（NP）中高度保守的氨基酸引起的。我们还能够通过反向遗传学鉴定出允许这些病毒有效繁殖的高度易感细胞系，从而产生重组的两种亚型的蝙蝠IAV。此外，我们发现MHCII是H18和h17介导的细胞进入的进入受体，并且可以表明来自各种蝙蝠和其他物种（包括猪和人类）的MHCII分子介导细胞进入。最后，我们观察到H18N11病毒在多种物种中感染和复制，包括小鼠、雪貂和蝙蝠。然而，特别是在小鼠中，病毒生长与N11头部结构域的缺失有关。总之，我们现在想解决以下主要的开放性问题：(a)除了MHCII之外，h18介导的细胞进入和内体释放还需要其他细胞因子吗？ (b)非典型蝙蝠流感na蛋白的功能是什么？ (c)蝙蝠IAV感染其他物种的潜力如何？ (d)蝙蝠IAV是否受宿主先天免疫限制因子（如MxA）的控制？通过这些重要的研究，我们将能够回答我们非常成功的第一个资助期的新问题。我们希望阐明这些新发现的蝙蝠流感病毒的分子生物学，并估计它们的溢出潜力。

The previous understanding of the influenza A virus (IAV) host range and diversity has recently been challenged by the discovery of two novel influenza subtypes in Central and South American bat species, provisionally designated H17N10 and H18N11. The surface glycoproteins of both subtypes lack the canonical receptor-binding and receptor-destroying activities of conventional hemagglutinin (HA) and neuramindase (NA) proteins, respectively.Virus isolation from infected bats or generation of recombinant viruses failed, impeding studies of their pathogenicity and zoonotic potential. We could show that bat chimeric viruses encoding HA and NA of conventional IAV fail to reassort with conventional IAV. In the first funding period, we identified the underlying mechanisms for this reassortment incompatibility, which is caused by highly conserved amino acids in the nucleoprotein (NP) of bat IAV. We were also able to generate recombinant bat IAV of both subtypes by reverse genetics after identifying highly susceptible cell lines that allowed the efficient propagation of these viruses. Furthermore, we discovered MHCII as an entry receptor for H18- and H17-mediated cell entry and could show that MHCII molecules from various bat and other species, including swine and humans, mediate cell entry. Finally, we observed that H18N11 viruses infect and replicate in various species, including mice, ferrets and bats. However, especially in mice, viral growth is associated with a deletion of the N11 head domain. In conclusion, we want to address now the following major open questions: (a) Are other cellular factors besides MHCII required for H18-mediated cell entry and endosomal release, (b) what is the function of the atypical bat flu NA-protein, (c) what is the potential of bat IAV to infect other species, and (d) are bat IAV controlled by host restriction factors of the innate immune such as MxA? With these important studies we will be able to answer the new questions from our very successful first funding period. We want to shed light onto the molecular biology of these newly discovered bat influenza viruses and also estimate their spill-over potential.