293T cells were transfected by using Lipofectamine 2000 reagent (Invitrogen) according to the manufacturer's protocol. A type I IFN production antagonist assay was performed as described previously [25] using IFNb-Luc and p55-C1B-Luc [34, 57] . 293T cells seeded on 24-well plates were transiently transfected with 50 ng of the luciferase reporter plasmid together with a total of 400 ng of various expression plasmids or empty control plasmids. As an internal control, 50 ng pRL-TK was transfected simultaneously. Then, 24 or 48 h later, the luciferase activity in the total cell lysate was measured by using the Dual-Luciferase Reporter Assay System (Promega) according to the manufacturer's directions.