Established mouse MAbs specifically recognized human CLDN1. HT1080 cells that expressed human CLDN1, CLDN2, CLDN4, CLDN5, CLDN6, CLDN7, or CLDN9 and mouse CLDN1-expressing L cells were incubated with anti-CLDN1 MAbs, i.e., 2C1, 3A2, 5F2, and 7A5, at 5 μg/ml and then treated with fluorescein isothiocyanate (FITC)-conjugated goat anti-mouse IgG. Gray and white patterns indicate vehicle- and Ab-treated cells, respectively.