Description
Annexin V is used as a probe to detect cells that have expressed phosphatidylserine (PS) on the cell surface, an event found in apoptosis as well as other forms of cell death. The Annexin V affinity assay typically uses a conjugate of annexin V and a fluorescent or enzymatic label, biotin or other tags, or a radioelement, in a suitable buffer (Annexin V binding to PS is Ca2+ dependent). The assay combines Annexin V staining of PS membrane events with the staining of the cell nucleus with PI or AAD-7 to distinguish living cells from dead cells. Annexin V apoptosis detection is based on the observation that soon after initiating apoptosis, cells translocate the membrane phosphatidylserine (PS) from the inner (cytoplasmic-facing) leaflet of the plasma membrane to the cell surface. Once on the cell surface, PS can be easily detected by staining with a fluorescent conjugate of Annexin V, a protein that has a high affinity for PS. Detection can be analyzed by flow cytometry or by fluorescence microscopy