BION-1 blocks high-affinity binding of GM-CSF to TF-1 and PBMNC. Scatchard transformation of saturation binding studies performed on (A) TF-1 cells or (B) PBMNC preincubated either alone (•) or in the presence of 1 μmol/L BION-1 MoAb (○) or 1 μmol/L of a control anti-β_c MoAb, 8E4 (▪) before the addition of radiolabeled GM-CSF. Binding assays were performed with¹²⁵I-labeled GM-CSF over a concentration range of 10 pmol/L to 10 nmol/L. The dashed line indicates the best fit for BION-1 noninhibitable binding and the solid line indicates the high-affinity GM-CSF binding in the absence of BION-1.