BST2 and infection: It is important to note that infection of macrophages with Vpu-defective virus led to a ~5-fold decrease in virus production due to the restriction exerted by BST2 on virus release (Fig. S5D); to avoid confounding effects resulting from BST2 restriction, viral infectivity was compared separately on WT and Vpu-defective viruses using the virus from untreated siRNA cells as control.