The proliferative states of circulating granulopoietic stem cells in man.

The fraction of granulocyte-macrophage colony-forming cells (CFC) in DNA synthetic phase in blood from 25 normal adults and those in blood and bone marrow from 8 haematologically normal subjects were evaluated by in vitro culture of cells with and without prior exposure to 3H-thymidine (12.5 muCi) for 1 h at 37 degrees C. The exposure of blood cells from normal adults to 3H-thymidine resulted in 26 +/- 10% reduction in colony formation and in 14 +/- 10% reduction in cluster formation. There was no difference in the magnitude of reduction in colony formation following exposure to 3H-thymidine by cells in blood and those in bone marrow in 6 of the 8 haematologically normal subjects. These findings indicated that about one fourth of the circulating CFC in normal adults are in proliferative state and that significant difference in proliferative states between CFC in blood and those in bone marrow probably does not exist in the majority of haematologically normal subjects.