Effect of HHV-7 and HIV-1 infection on surface CXCR4 expression in CD4⁺ T cells evaluated by flow cytometry. In (A) and (B), progressive downregulation of surface CXCR4 expression in HHV-7–infected SupT1 cells. In (B), surface CXCR4 was analyzed in combination with surface CD4. In (C), surface CXCR4 was analyzed either alone (top panels) or in combination with surface CD3 (middle panels) and surface CD4 (bottom panels) in CD8⁺-depleted primary cells, either uninfected or infected with HHV-7 (8 days PI). In (D), surface CXCR4 was analyzed in combination with surface CD4 in SupT1 cells, either uninfected or infected with HIV-1 (12 days PI). Data shown in (A) through (D) are representative of at least three separate experiments. Horizontal axis (logarithmic scale), relative surface CXCR4 expression detected by PE fluorescence intensity (in [A] through [D]). Vertical axis, relative cell number, isotype-matched control antibody staining, CD4 expression detected by FITC fluorescence intensity or CD3 expression detected by Cy5-PE fluorescence intensity, as indicated. Percentages of cells in the respective quadrants are indicated. Representative negative controls, constituted by cells stained with irrelevant isotype-matched MoAb, are shown in the top panels of (A) and (B).