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.

We next tested A549 human lung carcinoma cells expressing high levels of exogenous IFITM3 and observed that AmphoB (1 mM) produced a marked reversal of IFITM3-mediated restriction at both 12 and 24 hr postinfection ( Figure 1D ; Figures S1A-S1D). Similar results were seen with influenza B virus (data not shown). Due to decreased toxicity, liposomal preparations of AmphoB (AmBisome) are used to treat patients with fungal infections. Therefore, we investigated if AmBisome also rescued IAV infection from IFITM3. This was the case, as AmBisome's effect on IFITM3-mediated restriction was indistinguishable from that of AmphoB at a clinically relevant concentration (2 mM; Figure 1E ). Notably, therapeutically administered maximal concentrations of AmphoB and AmBisome range from 1 to 3 mM (Bellmann, 2007) . Given IFITM3's role in the IFN response, we determined the effect of AmBisome on IFNa-induced restriction of IAV ( Figure 1F ). IFN-a inhibited IAV infection in both the vector and IFITM3 cells, with the addition of AmBisome rescuing >60% of IAV infectivity, consistent with the 60%-80% of the IFN response that is lost with IFITM3 depletion (Brass et al., 2009) . Thus, AmBisome removes the majority of IFN's protection from IAV in vitro.