Abstract
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.
