Is thrombopoietin interleukin 6?

Recent data concerning to ability of interleukin 6 (IL-6) to stimulate platelet production have raised the possibility that platelet production is not specifically regulated by a unique feedback mechanism, but is part of a network encompassing several hemopoietic growth factors. Hypotheses are presented about the nature of thrombopoietin, its relationship to known growth factors, especially IL-6, and the specificity of a thrombopoietic response following change in the circulating platelet mass.