The Effect of Plethora on Growth and Differentiation of Normal Hemopoietic Colony-Forming Cells Transplanted in Mice of Genotype W/W^v

Suppression of erythropoiesis by transfusion of animals of genotype W/W^v was found to prevent the development of macroscopic spleen colonies following injection of normal coisogenic marrow cells. This inhibition of colony-formation was not due to a failure of colony-forming cells to proliferate in the absence of erythropoietic stimulation, since the growth rate of normal colony-forming cells in plethoric animals did not differ significantly from that seen in anemic hosts. It is likely that, in plethoric hosts, insufficient differentiated erythroblasts were produced to permit the development of macroscopically visible spleen colonies. Evidence was obtained that granulocytic differentiation proceeded during the growth of the transplanted colony-forming cells, and that this mode of differentiation was not affected by the suppression of erythropoiesis. These results indicate that both granulocytic differentiation and the process of selfrenewal by which colony-forming cells increase in numbers are controlled independently of the control of erythropoiesis. These experiments provide additional support for the view that colony-forming cells differ from erythropoietin-sensitive cells.