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!