Effect of TNF-α on HIV-Tat–induced adhesion molecules on EC. EC monolayers were incubated with treatment buffer, HIV-Tat (20 ng/mL), TNF (0.2 ng/mL) alone, or HIV-Tat plus TNF at 37°C for 6 hours. At the end of incubation, cells were harvested, fixed in 2% paraformaldehyde, and washed with cold PBS. The cells were resuspended in FACS binding buffer, and the expression of adhesion molecules was determined by flow cytometry as described in the Materials and Methods.