Dose-dependent effect of HIV-Tat on the expression of adhesion molecules on EC. EC monolayers were treated with various concentrations of HIV-Tat for 6 hours at 37°C. The cells were then harvested, fixed in 2% paraformaldehyde, and washed with cold PBS. Cells were resuspended in FACS binding buffer, and the expression of ICAM-1, VCAM-1, and ELAM-1 was determined by flow cytometry as described in the Materials and Methods.