Analysis of Apoptosis by Laser-Scanning Cytometry

One of the major goals in applications of cytometry in analysis of apoptosis is to identify and quantify dead cells and often to discriminate between apoptosis and necrosis. Recognition of dead cells relies on the presence of a particular biochemical or molecular marker that is characteristic for apoptosis, necrosis, or both. A variety of methods have been developed, especially for the identification of apoptotic cells (see reviews in refs. 1 –3 ). These methods were initially designed to be used by flow cytometry. The drawback of flow cytometric methods stems from the fact that identification of apoptotic or necrotic cells relies on a single attribute that is assumed to represent a characteristic feature (hallmark) of apoptosis or necrosis. However, this attribute may often be absent, particularly in the case of “atypical apoptosis,” which is common in the case of cells of epithelial or fibroblast lineage (e.g., refs. 4 –6 ). The apoptotic attribute may also be absent when apoptosis is induced by the agents that directly or indirectly suppress the appearance of this attribute. The characteristic changes in cell morphology (7 ), therefore, still remain the gold standard for recognition of apoptotic cell death.