The effect of interleukin 3 and GM-CSA-2 on megakaryocyte and myeloid clonal colony formation

Two separate helper T cell-derived lymphokines, interleukin 3 and granulocyte-macrophage colony-stimulating activity-2, were found to stimulate a broad and similar range of hemopoietic colonies in in vitro soft agar cultures including granulocyte, macrophage, granulocyte- macrophage, megakaryocyte, and mixed megakaryocyte colonies. Both lymphokines were potent stimulators of in vitro megakaryocyte colony formation. At plateau levels of IL-3, megakaryocyte colony formation was increased by biologic activity in pokeweed mitogen spleen- conditioned media.