Both endothelial cells (EC) and fibroblasts, two discrete populations of hemopoietic stroma, are known to modulate the proliferation and differentiation of hemopoietic progenitors. Recent reports also demonstrated that EC stimulate the in vitro growth of fibroblasts via a soluble factor. This finding seems to support the hypothesis that EC may play a role in the pathogenesis of bone marrow fibrosis in myeloproliferative disorders (MD).

We have studied the effects of the conditioned medium (CM) from human umbilical vein EC cultures, obtained in serum free conditions, on the growth of bone marrow fibroblasts from normal donors and from patients with MD. The results show that EC derived CM contains a factor which stimulates the proliferation of fibroblasts and that can act as an authentic growth factor by inducing “quiescent” fibroblasts to proliferate.

Moreover, we found that this endothelial derived growth factor (EDGF) equally promotes the proliferation of both normal and pathological progenitors of bone marrow fibroblasts (CFU-F) by increasing both the number and the size of the colonies.