Exclusive expression of G-CSF receptor on myeloid progenitors in bone marrow CD34+ cells

Although granulocyte colony-stimulating factor (G-CSF) has been reported to act on cells of neutrophilic lineage, the administration of G-CSF to induce the mobilization of various haematopoietic progenitors into the circulation. We analysed the expression of receptors for G-CSF (G-CSFR) on human bone marrow and G-CSF-mobilized peripheral blood CD34(+) cells, and examined the proliferation and differentiation capabilities of sorted CD34(+)G-CSFR+ and CD34(+)G-CSFR- cells using methylcellulose clonal culture. Flow cytometric analysis showed that G-CSFR was expressed on 14.9 +/- 4.9% of bone marrow CD34(+) cells, most of which were included in CD34(+)CD33(+) and CD34(+)CD38(+) cell fractions. In clonal cultures, CD34(+)G-CSFR+ cells produced only myeloid colonies, whereas CD34(+)G-CSFR- cells produced erythroid bursts, megakaryocyte and multilineage colonies. When incubated with the cytokine cocktail for 5 d, CD34(+)G-CSFR- cells generated CD34(+)G-CSFR+ myeloid progenitors. In G-CSF-mobilized peripheral blood, CD34(+) cells contained 10.8 +/- 5.8% of G-CSFR+ cells, most of which were also myeloid progenitors, although CD34(+)G-CSFR- cells contained a substantial number of myeloid progenitors. These results indicated that the expression of G-CSFR on CD34(+) cells is restricted to myeloid progenitors, suggesting that the specific activity of G-CSF on myelopoiesis depends on the exclusive expression of its receptor on myeloid progenitors, and that the mobilization of various haematopoietic progenitors is not a direct effect of G-CSF in humans.