Apoptosis or Programmed Cell Death (PCD) is an active, energy dependent process of cell death which occurs during development, in response to certain physiologic stimuli, and secondary to cell injury and stress (reviewed by Wyllie 1980, Arends and Wyllie 1991, Ellis et al. 1991,Wyllie 1992). This type of cell death occurs via controlled deletion of discrete cells within a tissue and plays a role in embryonic development and normal tissue homeostasis. It differs from necrotic cell death in that the cells eliminated by PCD die and are processed without initiation of an inflammatory response.