Effect of OPG pretreatment on leukocyte/endothelial cell adhesion and determination of Mac-1 expression in PMNs. (A) Endothelial monolayers or (B) PMNs were either left untreated or exposed to OPG (0.5 ng/mL) for the indicated times. After washing, PMNs and endothelial cells were cocultured for 1 hour, and the number of adherent PMNs was scored. Cell adhesion in untreated control culture was set as unity. Values are mean ± SD of triplicate determinations of 5 separate experiments. ∗, P > .05 versus control. (C) PMNs were either left untreated or exposed to OPG (0.5 ng/mL), and surface expression levels of Mac-1 on CD15⁺ cells was evaluated by double staining in flow cytometry. Irr. Abs: staining of the PMN culture with isotype-matched control antibodies. One of 3 experiments with similar results is shown.