GM-CSF induces eosinophilic cell growth-promoting activity on human fetal liver cells

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) has been described as a multi-lineage growth factor that induces in vitro colony formation of bone marrow erythroid burst-forming units (BFU-E), multipotential colony-forming units (CFU-GEMM), granulocyte-macrophage CFU (CFU-GM), granulocyte CFU (CFU-G), macrophage CFU (CFU-M), as well as eosinophil colony-forming units (CFU-Eo). Because of the preeminent role of the liver in fetal hematopoiesis, the effect of human recombinant GM-CSF (hrGM-CSF) on hematopoietic cells isolated from human fetal liver was tested in liquid cultures and in semisolid colony assays. hrGM-CSF induced a significant increase in the number of mature eosinophils in liquid culture and to a lesser extent in semisolid cultures when compared to untreated culture controls. The kinetics of this effect on eosinophils reached its peak on day 21 of culture. When GM-CSF and erythropoietin (Ep) were added simultaneously to the cultures, no significant change in the number of eosinophils compared to hrGM-CSF alone was observed. Ep or granulocyte colony-stimulating factor (G-CSF) did not show any CFU-Eo activity when added separately or simultaneously to both liquid and semisolid cultures. These results indicate that hrGM-CSF alone may be a potent stimulating factor for CFU-Eo obtained from human fetal liver and, in combination with other growth factors, control optimal development of human fetal eosinophils.