¹²⁵I–TNF-α and Daudi cells.

(A) Binding of ¹²⁵I–TNF-α to untreated Daudi cells. Specific binding (shown) was determined as total binding minus nonspecific binding. This experiment identifies 2 classes of specific binding sites with the binding capacities B_max1 = 30 fmol/10⁸ cells and B_max2 = 250 fmol/10⁸ cells with the correspondingK_d1 of 5 nM and K_d2 of 110 nM. (B) Binding of ¹²⁵I–TNF-α to Daudi cells after 1-day incubation with IFN-α. Binding capacity of the high-affinity site remained almost unchanged (B_max1 = 25 fmol/10⁸ cells, K_d1 =3 nM), whereas B_max2 of the low-affinity binding site increased to 550 fmol/10⁸ cells with a correspondingK_d2 of 120 nM. (C) Displacement of¹²⁵I–TNF-α binding to Daudi cells. Incubation of IFN-treated Daudi cells with ¹²⁵I–TNF-α (2.5 ng/mL) in the presence of increasing concentrations of unlabeled recCD95L (▴, 0.08-9.75 μg/mL), or anti-TNF antibody (●, 0.26-32.5 μg/mL), or recTNF-α (▪, 0.8-97.5 μg/mL), or recCD95:Fc (▾, 1.1-133.1 μg/mL) for 30 minutes at 4°C.