Fig. 9. Model of CD41 expression on various hematopoietic cell subsets. The results of the present studies lead us to predict a model whereby the primitive and definitive erythroid progenitor cells can be discriminated by the level of CD41 expression. Likewise, CD41 expression varies on long-term repopulating bone marrow stem cell subsets with the cells possessing the greatest repopulating ability expressing neither CD34 or CD41 (yellow cell) on the cell surface.