Figure 3.

Ligand binding activity of αLβ2 cysteine substitution mutants. (A) Binding of 293T transient transfectants to immobilized ICAM-1. (B) Binding of K562 stable transfectants to ICAM-1. Binding of the transfectants to immobilized ICAM-1 was determined in L15/FBS that contains Ca²⁺ and Mg²⁺ in the presence of the activating mAb CBR LFA-1/2 (10 μg/ml) or the control nonbinding IgG X63 (control), or in the absence of Ca²⁺ and Mg²⁺ and presence of 1 mM Mn²⁺ or 5 mM EDTA. Results are mean ± SD of triplicate samples and are representative of at least three experiments; some error bars are too small to be visible. (C) Binding of soluble ICAM-1-IgA Fc fusion protein (IC1–5D/IgA) to K562 stable transfectants. K562 transfectants were incubated with 100 μg/ml IC1–5D/IgA (Right) or control human IgA (Left), followed by incubation with FITC-labeled anti-human IgA and flow cytometry. Numbers on the upper right corner of each histogram plot are mean fluorescent intensity. Results are representative of three experiments.