Assessment of barrier integrity of Caco-2 monolayer cocultured with HTLV-1–infected or uninfected lymphocytes. Results shown are the means of 3 independent experiments. (A) Measurement of TER monitored with a volt-ohm meter at different times after coculture. Similar values of TER were found over time for Caco-2 cells cultured alone (diamonds) or with uninfected lymphocytes (triangles) or HTLV-1–infected lymphocytes (crosses) compared with the low values measured after EDTA treatment (squares). EDTA (12.5mM) was added 30 minutes before coculture with lymphocytes and used as a positive control to open the barrier. (B) Assessment of paracellular permeability of the Caco-2 monolayer monitored by FITC dextran (4 kDa) transfer to the basal compartment. No significant amounts of FITC dextran could be detected in the basal compartment for Caco-2 cells cultured alone (first column to the left) or with uninfected lymphocytes (third column to the left) or HTLV-1–infected lymphocytes (fourth column to the left). Opening of the barrier (positive control) was performed by adding EDTA in the apical medium, leading to a significant increase of permeability to FITC dextran (second column to the left).