The term 'apoptosis' describes the molecular and morphological processes leading to controlled cellular self-destruction and was first introduced in a publication by Kerr, Wyllie and Currie (Br. J. Cancer, 1972, 26: 239). 'Apoptosis' is of greek origin, having the meaning "falling off or dropping off", in analogy to leaves falling from trees or petals from flowers. By choosing this term, the authors might have intended to stress that this form of cell death is a natural phenomenon, an active and defined process which plays an important role in the regulation of the cell population in tissues upon physiological and pathological conditions. Apoptotic cell death can be induced by a variety of stimuli, such as ligation of cell surface receptors, starvation, growth factor/survival factor deprivation, heat shock, hypoxia, DNA damage, viral infection, and cytotoxic/chemotherapeutical agents. The apoptotic process is of widespread biological significance, and it was reported to be involved in embryogenesis, differentiation, proliferation/homoeostasis, removal of defect and therefore harmful cells, and especially in the regulation and function of the immune system. Thus, dysfunction or disregulation of the apoptotic program is implicated in a variety of pathological conditions, such as immunodeficiency, auto-immune diseases, neurodegenerative diseases, and cancer.
Apoptotic cells can be recognized by stereotypical morphological changes: the cell shrinks, shows deformation and looses contact to its neighbouring cells. Its chromatin condenses, and finally the cell is fragmented into compact membrane-enclosed structures, called 'apoptotic bodies' which contain cytosol, the condensed chromatin, and organelles. The apoptotic bodies are engulfed by macrophages and thus are removed from the tissue without causing an inflammatory response. This is in contrast to the necrotic mode of cell-death in which case the cells suffer a major insult, resulting in loss of membrane integrity, swelling and disrupture of the cells. During necrosis, the cell contents are released uncontrolled into the cell's environment what results in damage of surrounding cells and a strong inflammatory response in the corresponding tissue.
Frequently, the terms 'apoptosis' and 'programmed cell death' are used as synonyms. Programmed cell death was originally used in order to describe the locally and temporally defined cell death during embryogenesis. It was already in the middle of our century that cell death was recognized as a natural process in the development of organisms (Gluecksmann, 1951, Biol. Rev., 26: 59).

For a more detailed introduction to apoptotic cell death see the ApoReview - Introduction to Apoptosis!