Effect of HIV-tat (upper panel) and TNF (lower panel) on the adhesion of HL-60 cells to enodthelial cells. HL-60 cells were labeled with tritiated thymidine for 16 hours at 37°C. Labeled cells were washed, resuspended, and incubated (for 1 hour at 37°C) with EC monolayers pretreated with different concentrations of either TNF or HIV-tat for 6 hours at 37°C. Nonadherent cells were aspirated, and the monolayers were washed three times with HBSS, pH 7.4. The numbers of adherent cells were determined by solubilizing the cells and counting in a β scintillation counter. All determinations were made in triplicate.