Expression of cell-surface TF activity and antigen on polarized epithelial cells. (A) TF activity: The apical and basolateral surface domains of Caco-2 cells were incubated with VIIa (10 nmol/L) for 15 minutes at 37°C and TF/VIIa functional activity on each side was measured as the rate of Xa generation in the presence of 175 nmol/L factor X. Data are the mean ± SD of 4 independent experiments performed in duplicates. (B) Binding of ¹²⁵I-VIIa to cell-surface TF on polarized Caco-2 cells. Both compartments of polarized Caco-2 cells were incubated with 10 nmol/L of¹²⁵I-VIIa in the presence or absence of polyclonal anti-human TF IgG (100 μg/mL). VIIa bound to the apical (□) and basolateral (▪) surface was eluted by EDTA wash. The specific binding to TF was determined as described in Materials and Methods. Data are the mean ± SD of 5 independent experiments in duplicates. (C) Specific functional activity of TF/VIIa complexes. Specific functional activity of TF/VIIa complexes was calculated by relating the surface TF/VIIa activity with the number of VIIa molecules bound to cell-surface TF sites. Data are the mean ± SD of 4 independent experiments in duplicates.