Cellometer Annexin V-FITC / PI Apoptosis

Apoptosis, or programmed cell death, is a natural process of cellular self-destruction. Apoptosis is a part of routine cell turnover and tissue homeostasis, prevalent in epithelial cells, erythrocytes, and other cell
types genetically programmed to have a limited life span. It is also important in embryogenesis, maintenance of immune tolerance, and development of the nervous system. Apoptosis can be induced either by a stimulus, such as irradiation or toxic drugs, or by removal of a repressor agent. The cells
disintegrate into membrane-bound particles that are then eliminated by phagocytosis. Problems with the regulation of apoptosis are thought to be linked to many cancers, degenerative diseases, and autoimmune diseases, making apoptosis a key target in many fields of clinical research.

Necrosis is the death of cells or tissues from severe injury or disease, especially in a localized area of the body. Causes of necrosis include inadequate blood supply (as in infarcted tissue), bacterial infection,
traumatic injury, and hyperthermia.

Annexin V and propidium iodide are used to measure apoptosis and necrosis. Annexin V is a member of the annexin family of intracellular proteins that binds to phosphatidylserine (PS) in a calciumdependent manner. PS is normally only found on the intracellular leaflet of the plasma membrane in healthy cells, but during early apoptosis, PS translocates to the external leaflet. Fluorochrome-labeled Annexin V can then be used to specifically target and identify the PS on the surface of apoptotic cells.
Annexin V binding alone cannot differentiate between apoptotic and necrotic cells. Propidium Iodide (PI) solution is a membrane-exclusion dye that permeates cells with compromised cell membranes and binds to DNA. Early apoptotic and healthy cells with intact membranes will exclude PI, while late-stage apoptotic and necrotic cells with compromised membranes are stained. The use of both Annexin V-FITC and PI allows researchers to characterize a cell population based on % normal, % apoptotic, and % necrotic /very late-stage apoptotic cells.