Indirect immunofluorescence flow cytometry of untreated and HIV-Tat–treated EC. EC were treated with HIV-Tat (100 ng/mL) or treatment buffer alone for 6 hours at 37°C. The cells were then detached by a brief exposure to trypsin/EDTA, stained using monoclonal antibody to various adhesion molecules, and examined for the expression of ICAM-1, VCAM-1, and ELAM-1 by flow cytometry. The histogram shown by a broken line in all of the panels represents fluorescence profile of EC stained with isotype-matched IgG; the histogram shown by a solid line in all of the panels represents the fluorescence profiles of EC stained for various adhesion molecules.