Interferon-induced transmembrane proteins (IFITMs) can inhibit the cellular entry of several enveloped viruses, including simian immunodeficiency virus (SIV). The blockade of SIV by IFITMs is isolate-specific, raising the question which parameters impact IFITM-sensitivity. We show that the virion context in which SIV-Env is presented and the efficiency of virion incorporation determine Env susceptibility to inhibition by IFITMs. Thus, determinants other than the nature of the envelope protein can impact IFITM-sensitivity of viral entry.
The host cell encoded IFITM proteins can block viral entry and are an important component of the innate defenses against viral infection. However, the determinants controlling whether a virus is susceptible to blockade by IFITM proteins are incompletely understood. Our study shows that the amount of envelope proteins incorporated into virions as well as the nature of the virion particle itself can impact IFITM sensitivity of viral entry. These results show for the first time that determinants other than the viral envelope protein can impact IFITM sensitivity and have implications for the interpretation of previously published data on inhibition of viruses by IFITM proteins. Moreover, our findings might help to define the mechanism underlying the antiviral activity of IFITM proteins.