Binding of the influenza virion to the host cell

Influenza viruses bind via their surface HA (hemagglutinin) to sialic acid in alpha 2,3 or alpha 2,6 linkage with galactose on the host cell surface. Sialic acid in 2,6 linkages is characteristic of human cells while 2,3 linkages are characteristic of avian cells. The specificity of influenza HA for sialic acid in alpha 2,6 or alpha 2,3 linkages is a feature restricting the transfer of influenza viruses between avian species and humans. This species barrier can be overcome, however. Notably, passaged viruses adapt to their host through mutation in the receptor binding site of the viral HA gene.

流感病毒通过其表面的血凝素（HA）与宿主细胞表面上的唾液酸以α2,3或α2,6的连接方式结合，在连接的半乳糖上。2,6连接的唾液酸是人类细胞的特征，而2,3连接则是禽类细胞的特点。流感病毒血凝素对α2,6或α2,3连接唾液酸的特殊亲和力构成了限制流感病毒在禽类与人类之间传播的物种屏障。然而，这种物种屏障是可以被克服的。值得注意的是，经过传代的病毒通过其血凝素基因受体结合位点的突变来适应宿主。