Granulocyte colony-stimulating factor induces selective elevations of progenitor cells in the peripheral blood of mice.

The absolute numbers and relative frequencies of progenitor cells in six nonerythroid lineages were monitored in the peripheral blood (PB), bone marrow (BM), and spleen of Balb/c mice during 8 days of granulocyte colony-stimulating factor (G-CSF) injections. G-CSF induced a dose-related increase, up to 570-fold, in progenitor cell numbers in the blood and up to 620-fold rise of these cells in the spleen. The relative frequency of megakaryocyte progenitor cells was significantly increased in the blood compared with values in the BM or spleen. Time-dependent variations were also observed in the relative frequencies of three lineages of progenitor cells in the blood (megakaryocyte, granulocyte, and macrophage), but not in the BM or spleen. The consistent differences induced in the relative frequencies of various progenitor cell types between the blood, marrow, and spleen were independent of G-CSF dose. These data suggest that the increase in progenitor cells in the blood induced by G-CSF cannot simply be explained by a nonselective release of progenitor cells from the marrow or spleen.