Equilibrium binding of GM-CSF to the low- and high-affinity GM-CSF receptors. Binding assays were performed on COS cells transfected with cDNA encoding human low-affinity GMR (□), and on HL-60 promyelocytic cells expressing human high-affinity GMR/β (▪), with various concentrations of¹²⁵I-labeled GM-CSF at 23°C (A) and 4°C (B), as described in Materials and Methods. Representative Scatchard analyses of the binding data are shown. The k_d values of low-affinity GMR are 12.5 nmol/L (23°C) and 11.3 nmol/L (4°C), and the k_d values of high-affinity GMR/β are 22.9 pmol/L (23°C) and 291.5 pmol/L (4°C) in the presented data.