Characteristics of bone marrow fibroblastic colonies (CFU-F) formed in collagen gel

Characteristics of fibroblastic colonies formed in collagen gels following inoculation with bone marrow (BM) cells were examined. Fibroblastic cells could be easily distinguished from others, such as macrophages, from an early stage of culture. Most fibroblasts proliferated and formed colonies consisting of more than 50 cells within 7 days, later becoming adipocytes. The number of fibroblastic colonies was related to the number of inoculated BM cells (ten colonies/10(5) cells), and they were probably all monoclonal in origin. Histochemical and ultrastructural examinations revealed that the cells were BM fibroblasts or preadipocytes, and did not include endothelial cells. Macrophage colonies distinct from fibroblasts appeared together with the fibroblasts when more than 4 X 10(5) BM cells were inoculated per gel, and increased rapidly with increases in the number of inoculated BM cells.