During the early stages of apoptosis, cells loose their phospholipid membrane symmetry and expose phosphatidylserine at the cell surface while the plasma membrane remains intact. The exposure of phosphatidylserine on the outside of the cell can be monitored in cell suspensions using fluorochrome labelled Annexin V in flow cytometry (1,2,3)

Application:
Annexin V is used to detect apoptosis in cell suspensions by flow cytometry or immunofluorescence microscopy. The ability to monitor cell death is important in a wide variety of clinical situations.
One of the frequent applications is monitoring cell death during tumor therapy. For example, stimulation of apoptosis occurs when maligniancies are treated with cytotoxic drugs or ionizing radiation and in psoriasis by UV radiation. Understanding alterations in the cell death program may yield new approaches in therapy.
Cells may be programmed to die when they have lost growth regulation or experienced DNA damage due to radiation or drug action. Similarly self-reactive T-cells and virus-infected cells recognized by cytotoxic T-cells are all deleted to promote survival of the organism. The exposure of PS on the outside of the cell membrane is a signal to the surrounding phagocytes to remove the dying cell from the tissues. This exposure starts soon after the cell enters the apoptotic process, well before nuclear condensation and DNA cleavage become visible.

Specifications:
Annexin V is a phospholipid binding protein which exhibits high affinity and selective binding to phosphotidylserine in the presence of calcium ions. It is a highly specific marker of apoptosis.

References:
1. Koopman,G., et al 1994. Blood. 84, 1415-1420
2. Vermes,I., et al., 1995. J. Immunol. Methods, 180, 39-52
3. van Engeland, M., et al Cytometry, 1996. 24. 131-139

For research only. Not for use in humans. For in vitro use only