Figure 1.

Diagram of influenza A virus infection of the cell. Free extracellular influenza A viruses (1) containing hemagglutinin on their envelopes bind sialylated glycoprotein receptors on the host cell surface (2). The virus enters the host cell by receptor‐mediated endocytosis (2,3). The resulting endosome becomes acidified by proton transport (3), allowing fusion of the host and viral membranes (4). Blocking acidification of the virion with small molecule drugs is one means of inhibiting viral replication. Fusion is required for metabolism of the nucleocapsid (uncoating) (5) and release of the viral ribonucleoprotein complex into host cell cytoplasm (6). The viral RNA and associated viral proteins (including three polymerases) are transported to the nucleus (7). From here, positive‐stranded mRNA templates with poly(A) tails are synthesized (with and without host splicing) at the expense of most host protein synthesis and exported to the cytoplasm for translation (8). Newly synthesized viral ribonucleoproteins are exported to the cytoplasm for eventual virion assembly (9). Influenza A virus assembles and buds from the cell surface in a polarized fashion (eg, from apical surface of epithelial cells).