Granulocyte Colony-Stimulating Factor Induces hFcyRI (CD64 Antigen)- Positive Neutrophils via an Effect on Myeloid Precursor Cells

In this study we have examined hFcyRl expression during myelopoiesis. Normal bone marrow (BM) cells were found to express hFcyRl up to the metamyelocyte stage. A different FcyRl expression pattern was observed in an in vitro model of myelopoiesis. Purified CD34-positive BM cells, cultured for 12 to 14 days with granulocyte colony-stimulating factor (G-CSF), differentiate into a population of mature granulocytic cells. In these cultures, in which hFcyRl was virtually absent on the initial CD34-positive BM cells, hFcyRl was strongly induced by G-CSF after only 5 days. During final maturation the cells remained hFcyRl positive. This expression was confirmed functionally by antibodysensitized erythrocytes (EA)-rosette assays. Moreover, the mature myeloid cells were found to express mRNA encoding for hFcyRI, whereas reverse-transcriptase polymerase chain reaction analysis showed that both hFcyRlA and hFcyRlB genes were expressed. In contrast, on peripheral