Separation of spleen colony forming units (CEU-S) from mouse bone marrow cells using velocity sedimentation in an isokinetic gradient of Ficoll in tissue culture medium.

Spleen colony forming cells (CFU-S) from mouse bone marrow were concentrated using velocity sedimentation in an isokinetic gradient of Ficoll (polysucrose) in tissue culture medium. Following separation, CFU-S were found as a sharp modal population of cells which was discrete from the modal populations of lymphocytes and other cell types. Despite the wide separation of lymphocytes, granulocytes and CFU-S in the density gradient, there was no appreciable resolution of CFU-S specifically committed to erythroid, granulocytic or undifferentiated colony formation. This suggests that committed stem cells either share identical physical properties or are not detected by the spleen colony assay. In the purest fractions from the isokinetic gradient, CFU-S were 2.8- to 4.7-fold purified when compared with mouse bone marrow before separation.