Distribution of cells bearing receptors for a colony-stimulating factor (CSF-1) in murine tissues

CSF-1 is a subclass of the colony-stimulating factors that specifically stimulates the growth of mononuclear phagocytes. We used the binding of ¹²⁵I-CSF-1 at 0°C by single cell suspensions from various murine tissues, in conjunction with radioautography, to determine the frequency of binding cells, their identity, and the number of binding sites per binding cell. For all tissues examined, saturation of binding sites was achieved within 2 h at 2-3 x 10^-10 M ¹²⁵I-CSF-1. The binding was irreversible and almost completely blocked by a 2 h preincubation with 5 x 10^-10 M CSF-1. ¹²⁵-CSF-1 binding was exhibited by 4.3% of bone marrow cells, 7.5% of blood mononuclear cells, 2.4% of spleen cells, 20.5% of peritoneal cells, 11.8% of pulmonary alveolar cells and 0.4% of lymph node cells. Four morphologically distinguishable cell types bound ¹²⁵I-CSF-1: blast cells; mononuclear cells with a ratio of nuclear to cytoplasmic area (N/C)≥1; cells with indented nuclei; and mononuclear cells with N/C ≤ 1. No CSF-1 binding cells were detected among blood granulocytes or thymus cells. Bone marrow promyelocytes, myelocytes, neutrophilic granulocytes, eosinophilic granulocytes, nucleated erythroid cells, enucleated erythrocytes, and megakaryocytes also failed to bind. The frequency distribution of grain counts per cell for blood mononuclear cell was homogenous. In contrast, those for bone marrow, spleen, alveolar, and peritoneal cells were heterogeneous. The monocyts in blood or bone marrow (small cells, with either indented nuclei or with N/C > 1) were relatively uniformly labeled, possessing ~ 3,000 binding sites per cell. Larger binding cells (e.g., alveolar cells) may possess higher numbers of receptors. It is concluded that CSF-1 binding is restricted to mononuclear phagocytic cells and their precursors and that it can be used to identify both mature and immature cells of this series.