Influenza pandemic occurs when a new strain from other animal species overcomes the inter-species barriers and supports rapid human-to-human transmission. A critical prerequisite to this process is that hemagglutinin (HA) acquires a few key mutations to switch from avian receptors to human receptors. Previous studies suggest that H1 and H2/H3 HAs use different sets of mutations for the switch. This report shows that HA from the 1918 H1N1 pandemic virus (1918H1 HA) adopts the set of mutations used by H2/H3 HAs in receptor-preference switch when its 130-loop is made similar to those of H2/H3 HAs. Thus, the 130-loop appears to be the key determinant for the different mutations employed by pandemic H1 or H2/H3 HA. The correlation of the mutational routes and the 130-loop as unraveled in this study opens the door for efficient investigation of mutations required by other HA subtypes for inter-human airborne transmission.

当来自其他动物物种的新品系克服种间障碍并支持人与人之间的快速传播时，就会发生流感大流行。该过程的关键先决条件是血凝素（HA）需要获得一些关键的突变才能从禽类受体转换为人类受体。先前的研究表明，H1和H2 / H3 HA对开关使用不同的突变集。该报告显示，来自1918 H1N1大流行性病毒（1918H1 HA）的HA在其130环类似于H2 / H3 HA的情况下，在受体偏好开关中采用了H2 / H3 HA使用的一组突变。因此，130环似乎是大流行H1或H2 / H3 HA所采用的不同突变的关键决定因素。