DECAY-ACCELERATING FACTOR (CD55) AND MEMBRANE INHIBITOR OF REACTIVE LYSIS (CD59) ARE RELEASED WITHIN EXOSOMES DURING IN-VITRO MATURATION OFRETICULOCYTES

Exosomes are membrane vesicles released by reticulocytes during their maturation into erythrocytes. They have a clearing function because of their enrichment with some proteins known to decrease or disappear fr om the cell surface during maturation, eg, acetylcholinesterase (AChE) and transferrin receptor (TIR), respectively. To better understand th e molecular events leading to protein sorting in exosomes, we analyzed the expression of glycosylphosphatidylinositol (GPI)-anchored protein s on the exosome surface through a technique involving bead coupling a nd flow cytometry immunodetection. The presence of AChE, decay-acceler ating factor (DAF), membrane inhibitor of reactive lysis (MIRL), and l ymphocyte function-associated antigen 3 (LFA-3) on the surface of exos omes obtained from normal and paroxysmal nocturnal hemoglobinuria (PNH ) reticulocytes, suggests that (1) the GPI anchor is efficiently sorte d during exosome formation, (2) exosome release could account for the observed discrepancy in GPI-protein expression between reticulocytes a nd erythrocytes from PNH patients, and (3) exosomes could have another physiologic function related to controlling membrane attack complex f ormation. (C) 1998 by The American Society of Hematology.