Restriction factor required to restrict infectivity of lentiviruses, such as HIV-1: acts by inhibiting an early step of viral infection. Impairs the penetration of the viral particle into the cytoplasm (PubMed:26416733, PubMed:26416734). Enhances the incorporation of serine into phosphatidylserine and sphingolipids. May play a role in providing serine molecules for the formation of myelin glycosphingolipids in oligodendrocytes (By similarity). (Microbial infection) Upon HIV-1 infection, it is redirected to perinuclear region following interaction with HIV-1 Nef, excluding it from virions particles, thereby preventing subsequent antiviral defense activity (PubMed:26416733, PubMed:26416734). Localizes to the cell membrane, where it is efficiently incorporated into budding virions and impairs subsequent virion entry into target cells (PubMed:26416733, PubMed:26416734). Highly expressed in placenta, skeletal muscle, spleen, thymus, testis and peripheral leukocyte and is expressed weakly in the heart, liver and fetal brain. Belongs to the TDE1 family.