ERVW-1 and infection: To dissect the role of the VSV-G protein in the observed type I IFN response in our experimental system, we generated green fluorescent protein (GFP) reporter viruses that were pseudotyped with HIV-1 Env from the CCR5-tropic YU2 strain using method A. Infection of MDMs with this virus stock pseudotyped with HIV-1 Env induced type I IFN production (Fig. S2a).