TRAIL pretreatment alters inflammatory cytokine-mediated leukocyte adhesion. HUVECs were either left untreated or preexposed to TRAIL before stimulation with TNF-α or IL-1β for 18 hours. (A) Cells were treated with TRAIL (10 ng/mL) at the time of exposure to inflammatory cytokines (day 0) or 1 to 4 days before. (B) Dose-response effect of 3 days of TRAIL pretreatment (used at the indicated concentrations) was evaluated on HL-60 cell adhesion to HUVECs stimulated by either TNF-α or IL-1β. In panels A-B, cell adhesion in the absence of TRAIL pretreatment was set as 100%. In panels A-B, results are expressed as means ± SD of 3 independent experiments, each performed in triplicate. ^*P < .05. (C) TRAIL pretreatment does not affect surface expression of TNF receptors (TNF-R1 and TNF-R2). The control (open) histograms represent the background fluorescence obtained from the staining of the same cultures with isotype-matched control Abs. One of 4 experiments with similar results is shown. (D) Viability of endothelial cultures (treated as indicated) was assessed by MTT assay. Data are shown as average optical density (OD) ± SD.