Virus-Induced Apoptosis

Apoptosis of virus-infected cells may be important to block the spread of some virus infections in the host organism. Thus, virus-induced apoptosis can be a protective host defense mechanism. However, other viruses appear to thrive in apoptotic cells. In these circumstances, virus-induced apoptosis may also be harmful to the host—for example, when the virus itself does not kill the cell or when the virus infects a cell population that cannot be replenished. Thus, virus-induced programmed cell death also can contribute to the pathogenesis of disease. The striking morphologic changes and biochemical events that occur during virus-induced apoptosis do not significantly differ from those observed during apoptosis induced by other stimuli. Although viruses generally leave additional marks on the cell, cells dying by virus-induced apoptosis exhibit severe chromatin condensation around the periphery of the nucleus that is detectable with DNA stains and by electron microscopy. This chapter reviews the role of apoptosis in viral pathogenesis, the mechanisms by which viruses induced apoptosis, and the viral gene product that inhibit apoptosis. The chapter first describes the viral products that inhibit apoptosis as these are most familiar.