Detection of phosphatidylserine surface exposure on human erythrocytes using annexin V-ferrofluid

The asymmetric transbilayer distribution of phospholipids in the plasma mem brane and the regulation of phosphatidylserine (PS) exposure at the cell su rface of animal cells are of high physiological significance. It has been s hown previously that annexin V is one of the most sensitive tools with whic h the presence of small amounts of PS on the outer surface of eukaryotic ce lls can be detected. We present here the covalent coupling of annexin V mol ecules to magnetic nanoparticles of maghemite. The resulting annexin V-ferr ofluid is used in the magnetic separation of PS exposing cells, as illustra ted for human erythrocytes modified in their phospholipid transbilayer asym metry by the use of a calcium ionophore. Results on stored human erythrocyt es and comparison with results obtained using iodinated and fluorescein-lab eled annexin V are also presented. (C) 1999 Academic Press.