Fusion between cell membrane and liposomes containing the glycoproteins of influenza virus

Glycoproteins of influenza virus strains were incorporated into liposomes by a dialysis procedure, using octylglucoside as detergent. Liposomes containing either the cleaved or uncleaved hemagglutinin of the virus were tested for fusion activity with cellular membranes. Electron microscopic examination as well as microinjection studies revealed that liposomes containing the cleaved hemagglutinin could fuse with cell membranes. In contrast, liposomes containing the uncleaved hemagglutinin were merely adsorbed to the cell surface and fusion occurred only after treatment with trypsin. Native virus particles with the cleaved hemagglutinin could be shown to fuse with liposomes containing cellular receptors of influenza virus. From these results and the known correlation existing between cleavage of hemagglutinin and infectivity of influenza virus, it is suggested that fusion may be an important step in penetration of the nucleocapsid of influenza virus into host cells.