Apoptosis in leukocytes.

All cells of the hematopoietic system have finite life spans, shorter by far than that of the host. They end their lives by committing a form of cellular suicide or programmed cell death. The morphology of this process is considerably different from that of necrosis and is called apoptosis. Apoptotic cells undergo a stereotyped sequence of changes, including shrinkage and nuclear collapse. The cell is quickly recognized and eaten by a phagocyte, without the elicitation of an inflammatory response. Although most cells have specific triggers of apoptosis, the killer T cell seems able to induce apoptosis in any cell it recognizes. The process of apoptosis is regulated by cytokines, and may be modulated both in vitro and in vivo.