Granulocytic and monocytic differentiation of CD34(hi) cells is associated with distinct changes in the expression of the PU.1-regulated molecules, CD64 and macrophage colony-stimulating factor receptor

Abstract

The present study investigated the possibility that macrophage colony- stimulating factor (M-CSF) responsiveness of hematopoietic progenitor cells is regulated at the level of receptor expression and that M-CSF receptor (M- CSFR) may be used as an early marker of monocyte lineage commitment. Immunofluorescence measurements with an anti-M-CSFR antibody showed that 44% ± 5% of CD34(hi) cells expressed the receptor. The M-CSFR was present on progenitor cells that were positive for the granulo-monocytic marker CD64, but not on primitive, erythroid, or lymphoid progenitors. The CD34(hi)CD64+ population could be divided into subsets of M-CSFR(hi) and M-CSFR(lo) cells. In addition, a subset of CD34(hi)CD64-M-CSFR(hi) cells was found. CD34+ cells that were positive for M-CSFR, CD64, or both gave rise exclusively to granulo-monocytic cells, and 65% of the granulo-monocytic colony-forming cells in the CD34+ population were recovered from these cells. Approximately 70% of the colony-forming cells (CFCs) derived from CD34(hi)M-CSFR(hi) cells were macrophage colony-forming units (CFU-M), whereas 91% of the CFCs in the CD34(hi)CD64+M-CSFR(lo) population were granulocyte colony-forming units (CFU-G). The M-CSFR(hi) cells with the highest frequency of colony-forming and bipotent cells and largest average colony size were found in the CD64 subset, indicating that M-CSFR appears earlier than CD64 during monocyte development. After 60 hours in culture, a subset of the CD34(hi)M-CSFR(hi) cells had downmodulated M-CSFR (29% to 38%). This population gave rise almost exclusively to granulocytes, whereas the cells that remained M-CSFR(hi) gave rise exclusively to monocytes. In all experiments, the M-CSFR(hi) population responded to M-CSF, whereas minimal responses were observed among M-CSFR(lo) cells. These results suggest that M-CSF target specificity among human hematopoietic progenitor cells is determined by lineage-specific regulation of the M-CSFR and show that M-CSFR is a useful marker to discriminate between monocytic and granulocytic progenitor cells.