Characterization of mouse fetal liver granulocyte-macrophage colony-forming cells using velocity sedimentation

Fetal liver cells from CBA mice were separated by velocity sedimentation to determine the distribution and properties of granulocyte-macrophage colony-forming cells (GM-CFC). Twelve-day fetal liver GM-CFC separated into two peaks (s=7.7 mm/h, s=9.4 mm/h) in cultures stimulated by mouse lung conditioned medium (GM-CSF MLCM) or human urine (GM-CSFHU). Because fetal liver GM-CFC are of relatively light bouyant density, this finding indicates that fetal liver GM-CFC are much larger than corresponding cell in adult bone marrow (s=4.5 mm/h). By 18 days gestation more slowly sedimenting colony-forming cells were present (s=4.7 mm/h, s=6.0 mm/h). At all gestational ages, the most rapidly sedimenting (larger) colony-forming cells were more responsive to stimulation by GM-CSF MLCM than the smaller (slowly sedimenting) cells. Unlike the situation with adult marrow cells, velocity sedimentation achieved no segregation of GM-CFC according to the morphological type of colony produced.