PB2 and NP of North American H5N1 virus Drive Immune Cell Replication and Systemic infections

The 2022 North American outbreak of 2.3.4.4b H5N1 avian influenza virus revealed significant mammalian adaptation and pathogenicity, yet the mechanisms remain unclear. To address this knowledge gap, we investigated the North American H5N1 strain (GA/W22-145E/22), which demonstrated unique immune-cell mediated systemic dissemination, neuroinvasion, and 100% mortality in ferrets, unlike the non-lethal Eurasian strain (KR/W811/21). Genomic and reverse genetics studies identified PB2-478I and NP-450N mutations as key determinants of enhanced polymerase activity, immune cell tropism, and pathogenicity.Mutant GA/W22-145E/22 virus carrying PB2-478V/NP450-N showed complete survival without systemic dissemination. Furthermor, GA/W22-145E/22 demonstrated robust replication in human PBMCs and bovine mammary gland organoids, raising concerns about zoonotic spillover. These findings underscore PB2-478I and NP-450N as pivotal markers of pathogenicity, emphasizing the urgent need for enhanced surveilance and targeted interventions.

2022年北美暴发的2.3.4.4b分支H5N1禽流感病毒（H5N1 avian influenza virus）展现出显著的哺乳动物适应性与致病能力，但其致病机制仍未阐明。为填补这一研究空白，我们针对北美H5N1毒株GA/W22-145E/22展开研究：该毒株可通过免疫细胞介导全身性播散、发生神经侵袭，并在雪貂中引发100%致死率，这与仅导致非致死性感染的欧亚毒株KR/W811/21形成鲜明对比。基因组学与反向遗传学（reverse genetics）研究证实，PB2-478I与NP-450N突变是提升病毒聚合酶活性、增强免疫细胞嗜性与致病力的关键决定因素。携带PB2-478V/NP-450N的GA/W22-145E/22突变毒株，则可使受试雪貂完全存活且未出现全身性播散。此外，GA/W22-145E/22可在人外周血单个核细胞（peripheral blood mononuclear cells, PBMCs）与牛乳腺类器官（bovine mammary gland organoids）中实现高效复制，这引发了学界对其存在人畜共患病溢出（zoonotic spillover）风险的担忧。本研究结果明确PB2-478I与NP-450N是病毒致病力的关键标志物，凸显了加强相关监测与实施针对性干预措施的紧迫性。