SAA2 and infection: Four infection patterns were observed: A(H7N9) virus infected cells expressing SAα2,3-Gal receptors only (Fig. 3A), SAα2,6-Gal receptors only (Fig. 3B), both SAα2,3- and SAα2,6-Gal receptors (Fig. 3C), and neither SAα2,3- nor SAα2,6-Gal receptors (Fig. 3D).