Similarly, a negligible proportion of IC-HUVEC stained positive for p24-Gag in the absence of Tat (p24-Gag+ cells: 1.5%); however, when the infection was carried out in the presence of biologically active Tat, 23.9% of the cells stained positive for intracellular p24-Gag in flow cytometry (Figure 6). This evidence concerns the gene TAT and infection.