Delayed clearance of apoptotic lymphoma cells allows cross-presentation of intracellular antigens by mature dendritic cells.

Single cells are deleted from the midst of living tissue during normal turnover and embryogenesis. This event is not associated with inflammation or autoimmunity. Little is known of the clearance of apoptotic cells during dangerous situations, accompanied by extensive cell death and tissue damage: when macrophages are overwhelmed by apoptotic cells, other phagocytes, including immature dendritic cells (DCs), may become involved. DCs efficiently present antigens derived from the processing of internalized apoptotic bodies to class I- and class II-restricted T cells. Antigen presentation results either in T cell activation or in their functional blockade. The outcome is influenced by pro-inflammatory maturative signals: efficient T cell cross-priming requires fully mature DCs. Here we discuss in vitro data suggesting that the number of apoptotic cells that die at a given time influences DC maturation and therefore their ability to uptake antigens from apoptotic cells and cross-activate T lymphocytes.