Cell death: programmed, apoptosis, necrosis, or other?

There are at least two major types of active or physiological cell death. The most well-known form, apoptosis or Type I, involves early nuclear collapse, condensation of chromatin, generation of nucleosomal ladders, and cell fragmentation with little or no early alteration of lysosomes. It is most commonly seen in cells deriving from highly mitotic lines, and the cells are phagocytosed by neighboring cells or infiltrating macrophages. In metamorphosing or secretory cells, and under conditions where the majority of cells die, the bulk of the cytoplasm is consumed by expansion of the lysosomal system well before nuclear collapse is manifest. This form of cell death has been termed Type II cell death, and we revert to this terminology. The requirement for protein synthesis is more characteristic of Type II cell death in developmental situations than it is for Type I cell death. The variations seen force a reassessment of those aspects of physiological cell death that are truly universal, thereby focusing attention on the biology of the process. A better understanding of the biology and morphology of dying cells will help clarify the significance of the molecular and biochemical findings.