Scull Margaret A, Gillim-Ross Laura, Santos Celia, Roberts Kim L, Bordonali Elena, Subbarao Kanta, Barclay Wendy S, Pickles Raymond J
Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
PLoS Pathog. 2009 May;5(5):e1000424. doi: 10.1371/journal.ppat.1000424. Epub 2009 May 15.
Transmission of avian influenza viruses from bird to human is a rare event even though avian influenza viruses infect the ciliated epithelium of human airways in vitro and ex vivo. Using an in vitro model of human ciliated airway epithelium (HAE), we demonstrate that while human and avian influenza viruses efficiently infect at temperatures of the human distal airways (37 degrees C), avian, but not human, influenza viruses are restricted for infection at the cooler temperatures of the human proximal airways (32 degrees C). These data support the hypothesis that avian influenza viruses, ordinarily adapted to the temperature of the avian enteric tract (40 degrees C), rarely infect humans, in part due to differences in host airway regional temperatures. Previously, a critical residue at position 627 in the avian influenza virus polymerase subunit, PB2, was identified as conferring temperature-dependency in mammalian cells. Here, we use reverse genetics to show that avianization of residue 627 attenuates a human virus, but does not account for the different infection between 32 degrees C and 37 degrees C. To determine the mechanism of temperature restriction of avian influenza viruses in HAE at 32 degrees C, we generated recombinant human influenza viruses in either the A/Victoria/3/75 (H3N2) or A/PR/8/34 (H1N1) genetic background that contained avian or avian-like glycoproteins. Two of these viruses, A/Victoria/3/75 with L226Q and S228G mutations in hemagglutinin (HA) and neuraminidase (NA) from A/Chick/Italy/1347/99 and A/PR/8/34 containing the H7 and N1 from A/Chick/Italy/1347/99, exhibited temperature restriction approaching that of wholly avian influenza viruses. These data suggest that influenza viruses bearing avian or avian-like surface glycoproteins have a reduced capacity to establish productive infection at the temperature of the human proximal airways. This temperature restriction may limit zoonotic transmission of avian influenza viruses and suggests that adaptation of avian influenza viruses to efficient infection at 32 degrees C may represent a critical evolutionary step enabling human-to-human transmission.
尽管禽流感病毒在体外和离体条件下可感染人类气道的纤毛上皮，但禽流感病毒从禽类传播给人类的情况却很罕见。利用人类纤毛气道上皮（HAE）的体外模型，我们证明，虽然人类和禽流感病毒在人类远端气道温度（37摄氏度）下能有效感染，但禽流感病毒而非人类流感病毒在人类近端气道较低温度（32摄氏度）下的感染受到限制。这些数据支持了以下假说：通常适应禽类肠道温度（40摄氏度）的禽流感病毒很少感染人类，部分原因是宿主气道区域温度存在差异。此前，已确定禽流感病毒聚合酶亚基PB2中第627位的一个关键残基赋予了在哺乳动物细胞中的温度依赖性。在此，我们利用反向遗传学表明，第627位残基的禽源化会减弱人类病毒的活性，但无法解释32摄氏度和37摄氏度下不同的感染情况。为了确定禽流感病毒在32摄氏度时在HAE中受到温度限制的机制，我们构建了具有禽源或类禽源糖蛋白的、基于A/维多利亚/3/75（H3N2）或A/PR/8/34（H1N1）基因背景的重组人类流感病毒。其中两种病毒，即血凝素（HA）和神经氨酸酶（NA）具有来自A/鸡/意大利/1347/99的L226Q和S228G突变的A/维多利亚/3/75，以及含有来自A/鸡/意大利/1347/99的H7和N1的A/PR/8/34，表现出接近完全禽流感病毒的温度限制。这些数据表明，带有禽源或类禽源表面糖蛋白的流感病毒在人类近端气道温度下建立有效感染的能力降低。这种温度限制可能会限制禽流感病毒向人类的传播，并表明禽流感病毒适应在32摄氏度下的有效感染可能是实现人际传播的关键进化步骤。
