Anti-viral strategies of cytotoxic T lymphocytes are manifested through a variety of granule-bound pathways of apoptosis induction

Cytotoxic T cells and natural killer cells together constitute a major defe nce against virus infection, through their ability to induce apoptotic deat h in infected cells. These cytolytic lymphocytes kill their targets through two principal mechanisms, and one of these, granule exocytosis. is essenti al for an effective in vivo immune response against many viruses. In recent years, the authors and other investigators have identified several distinc t mechanisms that can induce death in a targeted cell. In the present artic le, it is postulated that the reason for this redundancy of lethal mechanis ms is to deal with the array of anti-apoptotic molecules elaborated by viru ses to extend the life of infected cells. The fate of such a cell therefore reflects the balance of pro-apoptotic (immune) and anti-apoptotic (viral) strategies that have developed over eons of evolutionary time.