ABSTRACT
In the adaptive immune response, virus-specific cytotoxic T lymphocytes are generated during the primary immune response to the virus and specifically kill infected cells through the release of cytotoxic granules similar to those of NK cells. Naive virus-specific CD8 T cells are activated to their effector status as cytotoxic T cells through engagement of the T-cell antigen receptor, which interacts with a complex of antigen-derived peptide and major histocompatibility complex (MHC) class I molecule at the surface of a cell presenting viral antigens. For naive CD8 T cells, however, engagement of T-cell receptors, although necessary, is not sufficient for activation. Strong co-stimulation by antigen-presenting dendritic cells together with co-stimulatory help from activated CD4 T cells are usually required to activate naive cytotoxic T cells.
