MURINE ENDOTHELIAL-CELLS SUPPORT FETAL LIVER ERYTHROPOIESIS AND MYELOPOIESIS VIA DISTINCT INTERACTIONS

Endothelial cells are an important component of the haemopoietic micro environment. To investigate how endothelial cells are involved in haem opoiesis, two established murine endothelial cell lines were assayed i n stromal cultures with fetal liver haemopoietic cells, Both endotheli al cell lines allowed for the proliferation and differentiation of ery throid and monocyte-macrophage precursors, suggesting that support for haemopoiesis is a general property of endothelial cells. Erythropoies is was dependent on the addition of erythropoietin (Epo), whereas myel opoiesis was independent of added Epo, Haemopoietic colonies developed in close contact with the endothelial cells. Erythroid colonies did n ot develop when transwell filters were used between the stroma and hae mopoietic cells, or when conditioned medium was used in place of strom al cells, In contrast, monocyte-macrophage colonies formed in the pres ence of transwell filters or conditioned medium, Thus close cell conta ct is necessary for erythropoiesis but not myelopoiesis under these co nditions. These results suggest that different molecular mechanisms ar e used by endothelial cells to support erythroid development and myelo id development in the mouse fetal liver.