Three distinct hematopoietic populations derived from normal bone marrow were analyzed for their response to defined growth factors. The Thy-1loT- B- G- M-population, composing 0.2% of bone marrow, is 370-fold enriched for pluripotent hematopoietic stem cells. The two other populations, the Thy-1- T- B- G- M- and the predominantly mature Thy-1+ T+ B+ G+ M+ cells, lack stem cells. Thy-1loT- B- G- M- cells respond with a frequency of one in seven cells to IL-3 in an in vitro CFU-C assay, and give rise to many mixed colonies as expected from an early multipotent or pluripotent progenitor. The Thy-1- T- B- G- M- population also contains progenitor cells which responded to IL-3. However, colonies derived from Thy-1- T- B- G- M- cells are almost exclusively restricted to the macrophage/granulocyte lineages. This indicates that IL-3 can stimulate at least two distinct clonogenic early progenitor cells in normal bone marrow: multipotent Thy-1loT- B- G- M- cells and restricted Thy-1- T- B- G- M- cells. Thy-1loT- B- G- M-cells could not be stimulated by macrophage colony-stimulating factor (M-CSF), granulocyte CSF (G-CSF) or IL-5 (Eosinophil-CSF). The hematopoietic precursors that react to these factors are enriched in the Thy-1- T- G- B- M- population. Thus, multipotent and restricted progenitors can be separated on the basis of the expression of the cell surface antigen Thy-1.

This content is only available as a PDF.