CUTTING EDGE - BYSTANDER APOPTOSIS TRIGGERS DENDRITIC CELL MATURATIONAND ANTIGEN-PRESENTING FUNCTION

Physiologic cell death via apoptosis occurs without inflammation or au toimmunity. Here, we investigated the outcome of the interaction of ap optotic cells with dendritic cells (DCs), which are potent professiona l APCs, DCs internalized apoptotic cells and processed them for presen tation to both MHC class I- and class II-restricted T cells with an ef ficiency that was dependent upon the number of apoptotic cells. The la tter event was accompanied by the autocrine/paracrine secretion of IL- 1 beta and TNF-alpha, with eventual DC maturation. High numbers of apo ptotic cells, mimicking a failure of their in vivo clearance, are ther efore sufficient to trigger DC maturation and the presentation of intr acellular Ags from apoptotic cells, even in the absence of exogenous ' 'danger'' signals.