Effects of human marrow stromal cells on proliferation by human granulocytic (GM-CFC), erythroid (BFU-E) and mixed (Mix-CFC) colony-forming cells.

We have investigated the effects of the major components of bone marrow stroma (fibroblasts, fat cells, macrophages and endothelial cells) on colony-forming haemopoietic precursor cells. Selective cultures of the different stromal cell types, grown to confluence, were used as underlayers for agar or methylcellulose cultures containing bone marrow cells. In different experiments, colony-stimulating factor (CSF) was added to stimulated granulocyte-macrophage colony-forming cells (GM-CFC), erythropoietin was used to induce erythroid burst (BFU-E) formation or erythropoietin and medium conditioned by leucocytes in the presence of phytohaemagglutinin (PHA-LCM) was added to induce the formation of colonies of mixed myeloid lineage (Mix-CFC). Fibroblasts grown from human marrow enhanced granulopoiesis when CSF was present in the cultures but suppressed the formation of BFU-E and mixed colonies. Treatment of the cultures with methylprednisolone induced the formation of fat cells in the fibroblast cultures and prevented both the fibroblast-mediated enhancement of granulopoiesis and the fibroblast-mediated suppression of erythropoiesis. Stromal macrophages reduced granulocyte colony formation but had little effect on the proliferation of BFU-E or mixed colony-forming cells. Endothelial cells stimulated granulopoiesis by releasing CSF into the culture supernatant; supernatant from endothelial cell cultures had no marked effects on either BFU-E or Mix-CFC. We conclude that different components of marrow stroma have contrasting effects on erythropoiesis and granulopoiesis; thus, marrow stroma may regulate the expression of stem cell differentiation in vivo.