Budding virion release

Once the mature virion has been assembled, it is ready for release from the cell. The release of certain viruses (c.g. poliovirus) is accompanied by lysis of the ho.st cell membrane and cell death. Some of the enveloped viruses, however. are released by budding m exocyloyis. a process involving fusion between the viral envelope and the cell mcmbiaiK This process is nearly a reversal nf the entry process the host cell membrane remains intact under these cxinditioos and the cell may survive. 

Rather uniquely, ICAM-1 is also subverted as receptor by human pathogens in at least three different ways. Major group rhinoviruses and A-type coxsackieviruses use ICAM-1 to release their RNA into the host cell cytoplasm. Erythrocytes infected by the malarial parasite Plasmodium falciparum, are able to bind ICAM-1 in the surface of endothelial cells (Berendt et al., 1992 Ockenhouse et al., 1992), and use this cytoadherence to sequester themselves in deep vascular beds, including the brain, minimizing exposure of the parasite to immune surveillance. Finally, human immunodeficiency virus-1 (HIV-1), uses ICAM-1 as a coreceptor (Bastiani et al., 1997 Fortin et al., 1997 Rizzuto and Sodroski, 1997). HIV-1 acquires several host cell membrane proteins when it buds from infected cells, making it possible for ICAM-1 to be incorporated into the envelope of the virions. This results in an increase of subsequent virus-cell interactions, enhancement of virus infectivity, and extension of the host cell range. 

A EXPERIMENTAL FIGURE 4-42 Progeny virions of enveloped viruses are released by budding from infected cells. In this transmission electron micrograph of a cell infected with measles virus, virion buds are clearly visible protruding from the cell surface. Measles virus is an enveloped RNA virus with a helical nucleocapsld, like rabies virus, and replicates as illustrated in Figure 4-41. [From A. Levine, 1991, Viruses, Scientific American Library, p. 22.]... 

Lymphocryptovirus (Epstein-Barr viruses). Rhadinovirus (saimiri-ateles-like virus). Enveloped, polyhedral, and dsDNA. Synthesis and maturation occur in the host cell nucleus, with budding through the nuclear envelope. Although most herpesviruses cause persistent infections, virions can be released by rupture of the host cell plasma membrane. 

---