The role of phagocytic cells in human blood leukocyte suspensions for in vitro colony-forming cells.

The iron ingestion method was used to separate colony stimulating cells from in vitro colony forming cells (CFU-C) in human white blood cell (WBC) suspensions. The depletion of phagocytic cells (granulocytes and monocytes) from WBC eliminated spontaneous colony growth, without influencing the total number of CFU-C. Thus, phagocyte-free human WBC can be used as a target for measuring human colony stimulating activity (CSA). Such leukocytes can be cryopreserved, thus making possible the use of standardized target cell preparations for longitudinal studies. Hemolysate added to phagocyte-free blood leukocytes did not induce colony formation but could enhance it in the presence of a suitable CSA. Spontaneous colony formation of unseparated WBC was significantly reduced by selective destruction of granulocytes by freezing in 10% DMSO, thus indicating that both granulocytes and monocytes are involved in the production of endogenous CSA in WBC suspensions.