Dissecting the hematopoietic microenvironment. VIII. Clonal isolation and identification of cell types in murine CFU-F colonies by limiting dilution.

In this study it was found that three kinds of cells, fibroblasts, endothelial cells, and macrophages, exist in fibroblastic colony-forming unit (CFU-F) colonies, consistent with the findings of others. However, when low enough bone marrow stromal cell numbers were cultured per dish, pure fibroblast, endothelial, and macrophage colonies were observed. When the cell number cultured in each dish was increased, all colonies were of mixed cell type. This evidence strongly suggests that the macrophages and endothelial cells contained in CFU-F colonies come from locally stimulated growth resulting in contamination and not from a common progenitor with fibroblasts or each other. In some longer term experiments, adipocytes were seen to appear within the colonies of late-passage pure fibroblast cultures.