Protective effect of G-CSF on apoptosis in irradiated fresh blood and leukapheresis granulocytes. Granulocytes were isolated from fresh blood, G-CSF (2 μg/mL) was immediately added to the medium. After 24 hours, the granulocytes were irradiated (or not) and subsequently assessed for apoptosis at the time intervals indicated. Apoptotic cells were identified as the population of granulocytes displaying typical reduced DNA content and reduced cell size. Percent vital cells means the percentage of all granulocytes showing no apoptosis in this test. The granulocytes can be divided into two populations. There is a significant (P < .05) increase in viability at 48 hours compared with 24 hours.