Figure 1.

Phosphatidylserine exposure on the outside of cells and microparticles – Phosphatidylserine (PS) is maintained on the inner surface of the plasma membrane of all cells. Several mechanisms can lead to the “exposure” of PS on the external surface of cells. Physiologic or pathologic “activation” of cells can lead to exposure of phosphatidylserine (PS) on the external surface of cells, or microparticles released by cells. Enveloped viruses bud from host cells, resulting in PS-bearing virions released into the intra- and extra-vascular spaces, depending upon the location of the infected cell.