Dendritic cells resurrect antigens from dead cells.

Antigens that do not normally access the cytoplasm of antigen-presenting cells, such as certain tumor and viral antigens, become targets of cytotoxic T lymphocytes (CTLs). Over the past 25 years, substantial evidence has emerged for an 'exogenous' pathway for loading MHC class I molecules. Dendritic cells are potent stimulators of T-cell responses and can induce CD8(+) CTLs by phagocytosis of dead tumor or virus-infected cells. Here, Marie Larsson and colleagues discuss the role of dendritic cells in stimulating MHC class I-restricted T-cell responses by exogenous routes.