Effect of Tat on RPE paracellular permeability. Vertical axis shows the basolateral-to-fluorescence ratio and the horizontal axis shows the time after the addition of the molecule. Data are mean and S.D. Values shown represent the mean ± S.D. of three independent assays or experiments. Control: D407 cells incubated with standard medium; 100 nM Tat: D407 cells treated with medium containing 100 nM HIV-1 Tat protein for 24 hours. (*P < 0.05).