Protein S protects the endothelial barrier integrity from OGD in an in vitro monolayer model of the human BBB. (A) Confocal scanning microscopy analysis of human endothelial monolayers 2 hours after normoxia or OGD with and without PS (100nM). ZO-1: green; F-actin: red; and nuclei; blue. Scale bar represents 10 μm. (B-C) Transmonolayer electrical resistance (TER) (B) and permeability coefficient (P) to FITC-dextran (C) in BBB monolayers during 2 hours of normoxia or OGD with and without PS (100nM). *P < .05, OGD − PS versus normoxia; #P < .01, OGD − PS versus OGD + PS. (D-E) PS dose-dependently enhances TER (D) and permeability to FITC-dextran in BBB monolayers 2 hours after OGD. Mean ± SEM, from 3 to 6 independent cultures.