Stimulators of megakaryocyte development and platelet production.

The range of known purified and cloned growth factors and their target cells within the megakaryocytic lineage is described. Data are reviewed outlining that megakaryocytopoiesis appears to be controlled at two levels: (i) by feedback control via circulating factors, and (ii) by factors within the marrow itself. Hypotheses are presented about the nature of thrombopoietin, its relationship to known growth factors, especially Interleukin-6 (IL-6), and the specificity of a thrombopoietic response following change in the circulating platelet mass.