FIGURE 7.

IL-4 induces claudin-5-dependent increase in electrical resistance of the EC monolayer, reducing the loss of barrier function caused by complement. A, TER measurements were performed continuously on EC monolayers in growth medium in duplicate (untreated) or with 1% FBS/DMEM alone (medium) or containing 10 ng/ml IL-4 (IL-4) in triplicate. Results are representative of three independent experiments. B, TER measurements of ECs that were pretreated with 10 ng/ml IL-4 or medium for 70 h, then washed and, at time 0, treated with 20% human serum (HS) or 20% heat-inactivated human serum (HI-HS). Then, TER measurements were continued for 2.4 h. Results are representative of two independent experiments. C, ECs were treated with the transfection reagent control or transfected with siRNA for β-actin or claudin-5, and when the cells reached confluence, medium or 10 ng/ml IL-4 was added, and incubation continued for 50 h. The bar graphs are normalized TER values at 50 h (means ± S.E. of four experiments). Filled circles are normalized TER values obtained before addition of medium or IL-4. Claudin-5 and β-actin down-regulation induced by specific siRNA was confirmed by Western blot. *, p < 0.02, normalized TER values at 50 h of IL-4-treatment versus medium.