Mouse Bone Marrow Stroma In Vitro Contains an Active Radiation - Sensitive Inhibitor of

SI/SId mice have a defective hemopoietic microenvironment. It has been assumed. based upon previous studies. that the primary abnormality in these mice is simply lack of a necessary supportive or inductive material within the hemopoietic stroma. We used in vitro long-term bone marrow cultures to characterize further the nature of the hemopoietic microenvironmental defect in Sl/Sld mice. SI/SId mouse bone marrow cells consistently produced <10% of the total hemopoietic cells and multipotent and unipotent hemopoietic progenitor cells produced in cultures of marrow from normal. congenic + I + mice. If fresh SI/SId and + I + marrow cells were mixed prior to establishing long-term marrow cultures. there was a direct correlation between number of SI/SId cells added and