Bone marrow stromal colony formation requires stimulation by haemopoietic cells

In mouse bone marrow cultures plated at low cell density, stromal colonies formed from colony-forming unit fibroblastic (CFUf) failed to develop unless the cultures were supplemented with irradiated feeder cells. Colony-stimulating activity was produced by irradiated bone marrow and spleen cells and by platelets, was dose dependent, not species specific and was maximal at high serum concentration. The efficiency of CFUf colony formation was 1.7 x 10(-4) for mechanically disaggregated and 14.6 x 10(-4) for trypsinised bone marrow cells. The colonies formed in the presence of feeder cells comprised hundreds of fibroblasts. In the absence of feeder cells, small fibroblast foci and single fibroblasts only were present in cultures. PDGF, IL-3 and EGF did not substitute for the colony-stimulating activity of feeder cells. These results suggest that CFUf colony formation requires growth factor(s) released by platelets and megakaryocytes which remain to be identified.