Permeability changes and MIF secretion of human endothelial HMEC-1 cells induced by DENV rNS1. DENV rNS1 (15 μg/ml), prepared as previously described , was incubated with HMEC-1 cells. The secretion of MIF in the medium was measured by ELISA at different time points as indicated. The permeability of HMEC-1 cells was determined by a transwell assay as previously described . Each point represents the mean ± SEM in duplicate.