ABSTRACT
T he regulated death of a cell is important in a variety of biological situations. Cell death is utilized in the selection of immunologicaUy competent T-and B-lymphocytes, in the sculpting or complete removal of tissues during development, and in cytotoxic T lymphocyte (CTL) killing. It is critical, in these situations, that cells die without releasing their internal contents, a process that would result in an inflammatory response and damage to neighboring cells. Cells undergoing one type of programmed cell death, apoptosis, avoid this potential hazard because apoptosis is a process composed of a carefully regulated set of morphological changes. Changes that occur in an apoptotic cell include shrinkage of cell volume, plasma membrane blebbing, chromatin condensation, nuclear pore aggregation, and breakdown of nuclear lamins. The flipping of phosphatidylserine from the inner to the outer plasma membrane targets cells for consumption by phagocytes. The result of this process is that cells are dismantled completely and neatly without producing any adverse effect on surrounding cells. The self-containment displayed by a cell undergoing apoptosis is what makes this process such an important biological tool.
