Effect of exposing HUVECs to flow for varying times on their response to TNF. Response was assessed by the percentage of adherent neutrophils transmigrating through the monolayer. HUVECs were cultured static (□) or exposed to shear stress of 0.3 Pa (▨) for 4, 8, or 28 hours. TNF (100 U/mL) was added for the last 4 hours, followed by flow-based adhesion assay. Data are mean ± SEM from 3 or 4 experiments of each duration. ANOVA showed significant effect of culture conditions on transmigration (P < .01). *P < .05, **P < .01 compared with results for static cultures by paired t test.