Different stimulative effects of human bone marrow and fetal liver stromal cells on erythropoiesis in long-term culture.

The factors determining the predominantly erythroid direction of human fetal liver hematopoiesis are unknown. We compared the capacities of human fetal liver and bone marrow stromas to sustain fetal and adult hematopoiesis in long-term cultures. In various marrow-fetal liver combinations of stroma and recharge, the maintenance of erythroid (BFU-e) and myeloid (CFU-GM) precursors in the nonadherent phase was determined. The morphology of the fetal liver nucleated cells during culture was also examined. This study shows that fetal liver stromas efficiently support fetal BFU-e for 6 to 7 weeks in vitro. Bone marrow stromas were not able to maintain fetal BFU-e beyond 4 weeks. Significant numbers of marrow BFU-e were not sustained in vitro on either source of stroma. On the other hand, the stroma layers of fetal liver and marrow origin were equally effective in maintaining fetal CFU-GM and adult CFU-GM in long-term culture. These findings show that the human embryonic liver stroma is a preferential site for stimulating fetal erythropoiesis. They do not demonstrate differences in stroma function to explain the relative paucity of myelopoiesis in the fetal liver.