Specific binding of [¹²⁵ I]Tat to monocytes and curve displacement with cold rTat and VEGF-A₁₆₅ . (A) Specific [¹²⁵I]Tat binding curve to monocyte at equilibrium and Schatchard analysis. For specific binding studies of Tat, human monocytes (1 × 10⁶/ 0.2 mL of binding buffer) were incubated with increasing concentrations of [¹²⁵I]Tat in the presence of a 100-fold excess of unlabeled ligand at 22°C for 120 minutes. At the end of incubation, cell suspension were overlayered on 0.5 mL of dibutylphtalate and centrifuged for 10 minutes at 13,000g, and the pellet was solubilized with 2% SDS in PBS was counted in a γ counter. (B) Ligand displacement curve at equilibrium of [¹²⁵I]Tat binding to monocytes by rTat and VEGF-A₁₆₅ . Human monocytes (1 × 10⁶) were treated in the same way as in (A) with 0.7 pmol of [¹²⁵I] without or with the indicated concentrations of unlabeled rTat (○) or VEGF-A₁₆₅ (•). Each experiment was repeated at least three times.