Simian Immunodeficiency Virus: General Features

Abstract

Simian immunodeficiency virus (SIV) was first isolated from captive rhesus macaques in 1984 and many strains have since been isolated from an assortment of nonhuman primates that inhabit sub-Saharan Africa. SIV belongs to the Lentivirus genus of the Retroviridae family and is the closest related retrovirus to human immunodeficiency virus (HIV-1), the etiologic agent of AIDS. Similar to other retroviruses, SIV replicates its genome through a proviral DNA intermediate and contains the standard retroviral genes, gag, pol, and env as well as the accessory genes tat, rev, vif, and nef. Some SIVs also encode the auxiliary gene products vpx and/or vpr. SIV uses CD4 as its receptor for entry and infects both CD4+ lymphocytes and macrophages. Although SIV infection of the natural host is usually not associated with disease, it causes both an acute and chronic illness similar to that caused by HIV in humans upon experimental infection of rhesus macaques. Multiple strategies of immune evasion are used by SIV to avoid clearance from the infected animal, including major histocompatibility complex downregulation, destruction of CD4+ help, and resistance to neutralizing antibodies. SIV represents the best existing animal model for AIDS and will undoubtedly play an important role in the development of an effective HIV vaccine.