Fig. 6.

Motifs in Vpu are critical for downregulation of CD28. Infected CD4⁺ Sup-T1 cells were stained for CD28 and analyzed by flow cytometry. Mean geometric fluorescence intensities (MFI) of cells were determined after gating on live and infected (Zombie Red^TM− and GFP⁺) cells. Cells infected with VSV-G pseudotyped NL4.3 lacking Nef (dNef, blue) and both Nef and Vpu (dNef dVpu, green) were used as controls. a Representative histograms illustrating cell surface CD28 on live (Zombie Red^TM−) infected (GFP⁺) cells. MFIs are indicated. b Mean (± SE) relative cell surface CD28 on cells infected with viruses encoding mutations in vpu (n ≥ 9). c Relative mean (± SE) total CD28 within cells infected with viruses encoding the indicated vpu mutations (n ≥ 7). d Western blot illustrating expression of mutated Vpu proteins. (Mr: molecular weight; UI: uninfected; SE: standard error; GAPDH: glyceraldehyde 3-phosphate dehydrogenase; MFI: geometric mean fluorescent intensity; GFP: green fluorescent protein; *p ≤ 0.05; **p ≤ 0.01; ****p ≤ 0.0001)