The most important changes are cell shrinkage, chromatin condensation, formation of cytoplasmic blebs and apoptotic bodies, and phagocytosis of apoptotic cells or bodies. A critical distinction, contrasting with necrosis, is the lack of inflammation. The DNA breaks down in a characteristic fashion yielding large pieces composed of 50-300 kilobases. These are further broken down as cellular enzymes known as endonucleases cleave the DNA into multiples of 180-200 bases. Finally, alterations of the cellular plasma membrane permit early recognition of these cells by macrophages, without the usual recruitment of inflammatory cells.
Apoptosis is associated with numerous disease states.
The following are the most well-researched examples. These complicated and sequential changes are orchestrated by a series of molecular events that are still being discovered. As of this writing, the following pathways have been elucidated. Transmembrane signals include binding to receptors for growth factors, cytokines, and hormones. Apoptosis initiated by intracellular signals include binding of glucocorticoids to nuclear receptors, physical agents such as heat, radiation, and hypoxia, and viral infections.