Neocytolysis and alterations of erythrocytes over a short term spaceflight

When a fast red cell mass reduction is needed, neocytolysis, i.e. destruction of young red blood cells (RBC), occurs. This process takes place in astronauts over the first days space-flight as part of the adaptive response to the microgravity environment. On blood samples drawn from four astronauts before and after a 12-15 days space-flight, we analysed a panel of hematological parameters and some phenotypic features of age-related RBC subsets, which can be linked to a neocytolytic process. After the space-flight, changes in plasma ferritin levels and in reticulocyte number indicated that a neocytolytic process likely occurred in flight. Furthermore the percentage and the viability of early generated RBC was decreased and on the outer membrane layer a small number of those left over exposed phosphatydilserine (PS), a phospholipid able to trigger macrophage ingestion. A decreased expression of the membrane molecules CD55, which protects red cells from complement mediated lysis and CD47, which inhibits macrophage phagocytosis, was also observed in young erythrocytes. It is likely that the membrane phenotype of early-generated RBC makes them more susceptible to destruction.