Granulocyte colony-stimulating factor augments in vitro megakaryocyte colony formation by interleukin-3

Granulocyte colony-stimulating factor (G-CSF) has been purified to homogeneity and the cDNA isolated. The reported properties of G-CSF have suggested that it is specific for the granulocytic lineage and only forms pure granulocyte colonies in in vitro cultures of murine bone marrow. We have demonstrated in this report that G-CSF augments the effect of interleukin 3 (IL3) on megakaryocyte formation. G-CSF alone had no stimulatory effect on megakaryocyte colony formation, however, the addition of G-CSF to IL3 in cultures of normal murine bone marrow increased the number of megakaryocyte colonies to 176% compared to cultures containing IL3 alone. Also, the combination of G-CSF plus IL3 stimulated the formation of larger megakaryocyte colonies than those formed in cultures of IL3 alone. In contrast, G-CSF had no effect on the number or size of megakaryocyte colonies stimulated by granulocyte-macrophage CSF. These results demonstrate that G-CSF augments the megakaryocyte colony formation of IL3, but not GM-CSF, and expands the lineage potential of G-CSF.