Although cell death is often seen as a pathological process, there are classically two types of cell death in biological systems, namely necrosis (accidental cell death) and apoptosis (programmed cell death). Although it was recognized from the early fifties that cell death was a natural process in normal tissue development and embryogenesis (1 ,2 ), the term apoptosis was first used by Wyllie et al. to describe a number of molecular and morphological processes in which individual cells actively undergo a programmed, genetically-regulated cell death (3 –5 ). The term, derived from a Greek word meaning “the dropping off of leaves from trees,” was thus introduced to distinguish this mode of death from the more familiar process of necrosis and to emphasize its physiological role (programmed cell death and apoptosis are often used interchangeably).
