[Programmed death of cells (apoptosis)]

Apoptosis is a mode of cell death defined by characteristic morphological, biochemical and molecular changes. It was first described as a "shrinkage necrosis", and then this term was replaced by apoptosis to emphasize its role opposite mitosis in tissue kinetics. During apoptosis the cell decrease in size, loose contact with neighboring cells, and loose specialized surface elements such as microvilli and cell-cell junctions. A shift of fluid out of the cells causes cytoplasm condensation, which is followed by convolution of the nuclear and cellular outlines. In later stages of apoptosis the entire cell becomes fragmented, forming a number of plasma membrane-bounded apoptotic bodies which contain nuclear and or cytoplasmic elements. The ultrastructural appearance of necrosis is quite different, the main features being mitochondrial swelling, plasma membrane breakdown and cellular disintegration. Apoptosis occurs in many physiological and pathological processes. It plays an important role during embryonal development as programmed cell death and accompanies a variety of normal involutional processes in which it serves as a mechanism to remove "unwanted" cells. Apoptosis is associated with prostate atrophy after castration or atrophy of the adrenal cortex and thymus after administration of glucocorticoids. Apoptosis is involved in elimination of CD4 T lymphocytes in the course of HIV infection. The interest in apoptosis in oncology stems from the fact that it occurs in tumors, spontaneously as well as triggered by different antitumor drugs, radiation or after withdraw of growth factors. Spontaneous apoptosis may play a role in evolution of tumor malignancy.(ABSTRACT TRUNCATED AT 250 WORDS)