BST2, also named as CD317 and Tetherin, belongs to the tetherin family. It may be involved in the sorting of secreted proteins and it is involved in pre-B-cell growth. BST2 is an antiretroviral defense protein, that blocks release of retrovirus from the cell surface. Depleted unpon HIV-1 infection by viral VPU protein through 20S proteasome degradation. Depleted upon infection by human Kaposi's sarcoma-associated herpesvirus (KSHV) through ubiquitination and subsequent degradation. BST2 may play a role in B-cell activation in rheumatoid arthritis. It is recently identified interferon-induced cellular proteins that restrict infections by retroviruses and filoviruses and of influenza virus and flaviviruses, respectively. BST2 is a plasma membrane proteins, tetherin inhibits virion particle release from infected cells. BST2 is effective against retroviruses and flavoviruses whilst IFITMs disrupt influenza and flavivirus infection.