Dose-response effect of OPG on leukocyte adhesion. HUVEC cells were either left untreated or exposed for 16 hours to the indicated concentrations of OPG. TNF-α (0.1 ng/mL) was used as positive control. After HUVEC washing, (A) PMNs or (B) HL-60 cells were added to the endothelial monolayer, and the percentage of adherent cells was determined after a coculture of 60 minutes at 37°C. Cell adherence on HUVECs is reported as fold of increase with respect to cell adhesion in the absence of treatment. Results are expressed as mean ± SD of 7 experiments, each performed in triplicate. ∗, P > .05.