Megakaryocytes derived from CD34‐positive cord blood cells produce interleukin‐8

In a serum-free liquid culture, thrombopoietin (TPO) selectively stimulated the growth of megakaryocytic cells from CD 34-positive cord blood cells. Using these cultured cells. we investigated cytokine production by human megakaryocytes. Day 10 megakaryocytes 12 x l0 5 secreted > 1000 pg/ml of interleukin (IL)-8, in contrast to small amounts of IL-1β and IL-6. A time-course study showed that the lL-8 production of megakaryocytes occurred at the late phase of the culture period. The megakaryocyte-conditioned medium had the chemotactic potential of polymorphonuclear leucocytes. which was abrogated by the addition of anti-lL-8 antibody, suggesting the secretion of biologically active IL-8. The combination of TPO and IL-lα was required for a significant augmentation of the IL-8 secretion. Direct evidence for IL-8 synthesis in megakaryocytes was provided by reverse transcription-polymerase chain reaction on purified CD41b + cells and by the detection of intracellular IL-8 in CD41b + cells. These results suggest that TPO stimulates not only the proliferation and differentiation of the progenitors capable of megakaryocytic lineage expression but also IL-8 release by the megakaryocytic cells with the aid of IL-1.