Binding of GM-CSF to G-CSF–elicited blood neutrophils from βc-null and WT mice. Cells were incubated with¹²⁵I-GM-CSF for 3 hours at 4°C and assayed for binding. Data were corrected for nonspecific binding and are shown plotted in the Scatchard coordinate system (•). (Top) Neutrophils (87% pure) from WT mice bound with a single class of high-affinity binding: kd = 500 pmol/L, n = 1,700 per cell. (Bottom) Neutrophils (83% pure) from βc-null mice bound GM-CSF only with low affinity: kd = 4.2 nmol/L, n = 2,100 per cell.