Monomeric BST-2 and non-glycosylated BST-2 are expressed at the cell surface and are sensitive to Vpu-induced down modulation. 293T cells were transfected with 0.1 μg each of wt BST-2, BST-2 C3A, or BST-2 N1/N2 together with 1 μg each of pEGFP-N1 in the presence or absence of 1 μg pcDNA-Vphu. All samples were adjusted to 5 μg total DNA with empty vector DNA. Cells were harvested 24 h after transfection and stained with an antibody to BST-2. As a control, 293T cells were transfected with pEGFP-N1 and empty vector in the absence of BST-2 and stained with BST-2 antibody (Ctrl). Samples were subjected to FACS analysis as described in Methods and gated for GFP-positive cells. The red line represents the control of GFP+/BST-2- cells. Blue lines represent BST-2 staining in the absence of Vpu and green lines indicate BST-2 staining in the presence of Vpu. Numbers in the boxed legends represent mean fluorescence intensities for each sample.