Recombinant human c-Mpl ligand is not a direct stimulator of proplatelet formation in mature human megakaryocytes.

To evaluate the effect of the c-Mpl ligand on platelet production by megakaryocytes, we investigated proplatelet formation in isolated human megakaryocytes cultured in serum-free medium, with or without the c-Mpl ligand, interleukin-6 and erythropoietin. When interleukin-6 was added to the culture medium, the percentage of megakaryocytes displaying proplatelets was approximately 1.5-fold the control value; whereas, in the presence of the c-Mpl ligand, the percentage of megakaryocytes displaying proplatelets decreased in a dose-dependent manner and did not increase compared to control values at any dose tested. However, the viability of megakaryocytes after a 4 d culture in the presence of the c-Mpl ligand was significantly higher than that of the cells cultured without it. The c-Mpl ligand did not stimulate the proplatelet formation in megakaryocytes in vitro.