Granulocyte-macrophage colony-stimulating factor is not responsible for residual thrombopoiesis in mpl null mice

Abstract

Objective. To examine the role of granulocyte-macrophage colony-stimulating factor (GM-CSF) in thrombopoiesis. Materials and Methods. Thrombopoietin-unresponsive mice (mpl null mice), which have a profound reduction in platelets and mature megakaryocytes, were interbred with mice that do not respond to GM-CSF or interleukin 5 (βc null mice), and hematopoiesis was examined. Results. In initial experiments on a mixed genetic background, double mutant mice (βc/mpl null mice) showed an unexpected amelioration of the thrombocytopenia seen in mpl null mice. Platelet counts were elevated approximately twofold in βc/mpl null mice compared with mpl null mice (mpl null 73 ± 31; βc/mpl null 164 ± 70; n..