IFITM3 and infection: In addition to blocking infection through inhibition of virus entry into cells, IFITM3 also performs an antiviral function in cells that are already infected—it has been shown to interact with and inhibit the function of viral fusogens (known as viral envelope glycoproteins) found in virions, which in turn reduces the infectivity of said virions (Compton et al, 2014; Tartour et al, 2014; Wang et al, 2017; Yu et al, 2015).