Effects of conditioned medium derived from endothelial cells overexpressing or lacking ATF4 on THP-1 cell migration. A). Mouse retinal endothelial cells were transduced with Ad-Ctrl or Ad-ATF4 for 24 h. B). Brain endothelial cells isolated from ATF4 +/+ or ATF4 −/− mice were challenged with 250 ng/ml LPS for 24 h. The medium was collected from endothelial cell culture and used for THP-1 cell migration assay as described in the Method section. Left panels: representative images of migrated THP-1 cells (200×). Right panels: The numbers of migrated cells were quantified from 3 independent experiments. Results are expressed as mean ± SD (n = 3). ** P < 0.01 vs. Ad-Ctrl or WT; ++ p < 0.01 vs. WT + LPS.