Quantifying Interferon Levels in Virus-Inactivated Supernatant

Media were removed from cells before treatment with Universal IFN-I or human IL-29/IFN Lambda 1 (IFN-III) (both from PBL Assay Science, Piscataway, NJ, USA) diluted in DMEM supplemented with 2% HI FBS and at the concentrations indicated in the figure legends. Prior to quantifying biological levels of IFN-I from the supernatant of infected cells, inactivation of virus was performed. Briefly, the indicated supernatant was acid treated with 1N HCl at room temperature for 30 min, followed by titration with 1N NaOH to achieve neutralization of acid. IFN-I was subsequently quantified in virus-inactivated supernatant using HEK-Blue™ IFN-α/β indicator cells (Invivogen) and QUANTI-Blue™ reagent (Invivogen), as previously described [11 (link)].