Cell Death: The Significance of Apoptosis

Abstract

1. It is feasible to categorize most if not all dying cells into one or the other of two morphologically distinct modes: necrosis and apoptosis. What is known of the incidence and mechanism of these processes supports the conclusion that they are fundamentally different phenomena. 2. Necrosis involves cellular dissolution following collapse of internal homeostasis. The mechanisms underlying apoptosis are less clear but differ from those in necrosis in that (a) the process is frequently triggered by physiological stimuli, (b) depletion of cellular energy supply is not necessary, and (c) in the cell systems for which information is available, a step involving macromolecular synthesis is essential. 3. Because apoptosis occurs in vivo in single cells surrounded and outnumbered by viable neighbors, most studies have been restricted to its morphology. The process is of widespread incidence and apparently great biological significance, however, and merits more intensive investigation of its mechanisms. 4. Promising cell culture systems now exist in which apoptosis can be generated in numbers of cells sufficiently large for biochemical study. Such systems are likely to provide information on the requirement for new gene expression in initiation of apoptosis, the properties of the endonuclease whose activation is associated with the chromatin condensation, the mechanisms underlying the cytoplasmic contraction, and the recognition of apoptotic cells by phagocytes. © 1980, Academic Press Inc.