Endogenous OPG release by endothelial cells. (A) HUVECs were either left untreated or stimulated with the indicated concentration of TNF-α. After 24 hours, the levels of OPG released in culture supernatant were measured by ELISA. Results are expressed as means ± SD of 4 independent experiments, each performed in triplicate. (B) HUVECs were either left untreated or stimulated with OPG (0.5 ng/mL) in the presence or absence of TNF-α. After washing, leukocytes were added to endothelial monolayer, and the number of adherent leukocytes was scored. Values are mean ± SD of triplicate determinations of 3 separate experiments.