NEW INSIGHTS INTO THE REGULATION OF MEGAKARYOCYTOPOIESIS BY HEMATOPOIETIC AND FIBROBLASTIC GROWTH-FACTORS AND TRANSFORMING GROWTH FACTOR-BETA-1

Effects of cytokines on murine megakaryocyte (MK) colony formation from either unfractionated marrow cells or purified early haematopoietic cells were studied. Recombinant interleukin-3 (IL3), interleukin-6 (IL6), granulocyte-macrophage colony-stimulating factor (GM-CSF), erythropoietin (Epo) and acidic and basic fibroblast growth factor (aFGF and bFGF) each was able to stimulate MK colony growth although they varied somewhat in their potential. IL6 and FGFs, in addition to their effect on MK colony growth. increased the size of individual MK. The combination of IL3 with IL6 or FGF resulted in an additive action. Monoclonal anti-IL6 antibody completely neutralized the activity of mouse IL6 and FGFs but had no effect on human IL6, mouse IL3 and GM-CSF. When using purified lineage negative marrow cells, only IL3 and IL6 promoted MK colony formation. Transforming growth factor beta-1 (TGF-beta-1) at 10-200 pg/ml selectively inhibited IL3-induced MK colony formation, and at 0.2-0.5 ng/ml it still had no obvious effect on the activity of IL6 or GM-CSF but caused an inhibition of FGF-induced MK colony formation. These data suggest that differential mechanisms are involved in the regulation of megakaryocytopoiesis by IL3, IL6, FGFs and GM-CSF, and that TGF-beta-1 negatively regulates MK development mainly by interfering with the action of IL3.