Quantitative analysis of thrombopoietin receptors on human megakaryocytes.

Thrombopoietin (TPO), or c-MPL ligand, is the primary regulator of megakaryocyte and platelet production. TPO receptors expressed on human megakaryocytes derived from peripheral blood (PB) and cord blood (CB) progenitors cultured in the presence of TPO have now been analyzed quantitatively. Like those on human PB platelets, TPO receptors on the cultured megakaryocytes exhibited a molecular mass of approximately 80 kDa. Various characteristics of PB- and CB-derived megakaryocytes indicated that the former were more mature than the latter. Both PB- and CB-derived megakaryocytes expressed a single class of high-affinity TPO receptors, with 1933 +/- 772 (n = 3) and 184 +/- 48 (n = 4) sites per cell, respectively. These data indicate that the number of TPO receptors on human megakaryocytes increases with cell maturation.