Amphotericin B Increases Influenza A Virus Infection by Preventing IFITM3-Mediated Restriction

Lin, Tsai-Yu; Chin, Christopher R.; Everitt, Aaron R.; Clare, Simon; Perreira, Jill M.; Savidis, George; Aker, Aaron M.; John, Sinu P.; Sarlah, David; Carreira, Erick M.; Elledge, Stephen J.; Kellam, Paul; Brass, Abraham L.

While treating fungal infection of our tissue culture cells with the antimycotic AmphoB we noticed that the previous differences in the levels of IAV infection due to differing levels of IFITM3 were surprisingly erased. AmphoB has been used to treat systemic fungal infections, including Aspergillosis, since the 1950's, and its clinical formulations are currently used widely to treat a growing number of such cases (Bellmann, 2007) . AmphoB's mechanism of action is thought to involve its binding to the fungal membrane constituent, ergosterol, leading to pore formation and ion egress (Bolard, 1986) . In the clinic, AmphoB treatment produces severe side effects because of the formation of such membrane-spanning pores, which increase in diameter as a function of concentration, with low concentrations (0.1 mM) permitting Na + and K + to traverse and higher levels (>5 mM) allowing the passage of larger cations (e.g., Ca +2 and H 3 O + ). To overcome this toxicity, two liposomal preparations of AmphoB, AmBisome and Abelcet, were developed, both of which manifest reduced side effects by preferentially targeting fungal membranes. AmBisome is thus a first-line therapy for systemic fungal infections with an estimated $330 million in annual sales worldwide (Moen et al., 2009) . Of note, after commencement of our investigations, AmphoB was reported to increase IAV replication in vitro; however, both the mechanism and the in vivo implications of this phenomenon remain obscure (Roethl et al., 2011) . Therefore, intrigued by our observations regarding IFITM3's neutralization by AmphoB, we pursued studies to elucidate both the mechanism of this interaction and its potential in vivo consequences.