Cell Analysis 

Background information
The Annexin V conjugates selectively label apoptotic, necrotic, and dead cells through the specific binding of Annexin V to phosphotidylserine (PS). In most normal, viable eukaryotic cells, the negatively charged phospholipid PS is located in the cytosolic leaflet of the plasma membrane lipid bilayer.1 PS redistribution from the inner to the outer leaflet is an early and widespread event during apoptosis. However, in necrosis, PS becomes accessible due to the disruption of membrane integrity.2 Apart from necrosis and apoptosis, PS also becomes accessible in activated platelets, in certain cell anomalies like sickle cell anemia, in erythrocyte senescence, upon degranulation of mast cells, and in certain stages of B cell differentiation. PS exposure by apoptotic cells serves as a trigger for the recognition and removal by macrophages.
Annexin V is a 35 kDa phospholipid-binding protein and has a high affinity for PS in the presence of physiological concentrations of calcium (Ca2+).