L-cell colony-stimulating factor (CSF) is identical to macrophage growth factor and stimulates macrophage proliferation (Stanley et al., 1976, J. Exp. Med. 143: 631-647). The nature of the interaction of iodinated L-cell CSF (125I-CSF) with murine peritoneal exudate macrophages was studied. On incubation with 10 pM 125I-CSF at 0°C, cellular binding of 125I-CSF reaches a stable maximum within 15 h. This is in contrast to the association behavior at higher temperatures. At 37 °C, cell-associated 125I-CSF levels reach, within 45 min, an unstable maximum which is up to 10-fold less than that occurring under the same conditions at 0°C. At 0°C, binding is saturated (~5 X 104 sites/cell) at CSF concentrations of 1 nM. A comparison of binding and competition experiments indicates that iodinated L-cell CSF binds as effectively as L-cell CSF and that human urinary CSF and L-cell CSF equipotently compete for 125I-CSF binding. Specificity of the CSF-binding site is demonstrated by the failure of other known growth factors and hormones to compete for 125I-CSF binding. These studies and other findings suggest that 125I-CSF binding is restricted to macrophages and their precursors and to macrophage cell lines and that the binding site(s) is the receptor mediating the biological action of this CSF.
ASJC Scopus subject areas
- Cell Biology