Thrombopoietin has a differentiative effect on late-stage human erythropoiesis

To further explore the mechanism of the effect of thrombopoietin (TPO) on e rythropoiesis, we used a two-phase culture system to investigate the effect of TPO on late-stage human erythroid lineage differentiation. In serum-fre e suspension and semisolid cultures of human peripheral blood derived eryth roid progenitors, TPO alone did not produce benzidine-positive cells, Howev er, in serum-containing culture, TPO alone stimulated erythroid cell prolif eration and differentiation, demonstrated by erythroid colony formation, pr oduction of benzidine-positive cells and haemoglobin (Hb) synthesis. Monocl onal anti-human erythropoietin antibody and anti-human erythropoietin recep tor antibody completely abrogated the erythroid differentiative ability of TPO in the serum-containing systems. This implied that binding of EPO and E PO-R was essential for erythropoiesis and the resultant signal transduction may be augmented by the signals emanating from TPO-c-Mp interaction. Exper iment of withdrawal of TPO further demonstrated the involvement of TPO in l ate-stage erythropoiesis. RT-PCR results showed that there was EPO-R but no t c-Mpl expression on developing erythroblasts induced by TPO in serum-cont aining system. Our results establish that TPO affects not only the prolifer ation of erythroid progenitors but also the differentiation of erythroid pr ogenitors to mature erythroid cells.