Since we found that primary isolates of Nef obtained from acute clade C, clade D, and clade F HIV-1 infection were capable of counteracting HIV-1 restriction by IFITM3 (Figure 1A), we next examined Nef proteins from clade B HIV-1, which is the predominant form of HIV-1 in North America. This evidence concerns the gene S100B and HIV-1 infection.