PREPARATION, PROPERTIES, AND APPLICATIONS OF RECONSTITUTED INFLUENZA-VIRUS ENVELOPES (VIROSOMES)

This chapter discusses the preparation, properties, and applications of reconstituted influenza virus envelopes (virosomes). Enveloped viruses utilize a membrane fusion strategy to introduce their genome into the cytoplasm of the host cell. This infectious entry, in principle, can occur through direct fusion of the viral envelope with the cell plasma membrane, or it may occur from within endosomes after cellular uptake of intact virions through receptor-mediated endocytosis. In the latter route of entry, the target membrane for fusion of the viral envelope is the limiting membrane of the endosomal cell compartment. The expression of the fusion activity of the virus is strictly dependent on a mildly acidic pH, precluding direct fusion of the viral envelope with the plasma membrane. After endocytic uptake, the virus encounters an acidic environment in the lumen of the endosomes, activating its fusion capacity. In addition, the membrane fusion activity of influenza virus is mediated solely by the major envelope glycoprotein, hemagglutinin (HA). HA represents the best-characterized membrane fusion protein. © 1993, Elsevier Inc. All rights reserved.