Caco-2 cells were grown on transwell inserts at 1.5×105 cells/cm2. (A) Transepithelial electrical resistance (TEER) was measured to assess monolayer integrity. Data are shown as means ± S.E.M; n=3. (B) Fluorescence microscopy of tight junctions immunolabeled with anti-occludin and Texas Red-labeled secondary antibody, on Days 5 or 14 (low versus high TEER values, respectively). Reproduced from Ghaffarian et al., J Controlled Rel, 2012, 163(1):25–33.