Avidity of anti-ICAM carriers toward endothelial cells. Fixed activated HUVECs were incubated for 1 h or 3 h at room temperature with various concentrations (0.5 fM to 1.08 nM) of anti-ICAM carriers with diameter: (A) 4.5 μm (34,000 anti-ICAM/μm2 carrier surface), (B) 1 μm (30,000 anti-ICAM/μm2), (C) 1 μm (13,000 anti-ICAM/μm2), or (D) 250 nm (7,700 anti-ICAM/μm2). Binding was quantified from microscopy (see Materials and Methods). Data are mean ± SEM, for which regression curves were fitted in order to determine the dissociation constant (Kd) and maximal binding at saturation (Bmax). The regression coefficient (R2) is shown.