TFPI expression on polarized Caco-2 epithelial cells. (A) Cell-surface–associated TFPI: The apical and basolateral cell surfaces were treated with 500 μL 0.1 mol/L glycine pH 3.0 for 3 minutes to remove cell-surface–associated TFPI. Eluates were removed from the dish and pH was adjusted to 7.8 with 1 mol/L Tris and assayed for TFPI activity. Data are the mean ± SD of 4 independent experiments. (B) Effect of anti-TFPI on cell-surface TF/VIIa functional activity: Caco-2 cells grown in transwells were treated with control IgG (circles) or with polyclonal anti-TFPI antibodies (100 μg/mL) (squares) for 30 to 60 minutes on both the apical (open symbols) and basolateral (closed symbols) surfaces, and a Xa generation assay was performed as described in the legend to Fig 1. Data are the mean ± SD of 5 independent experiments.