Detection of type I IFN by ELISA and HEK-blue type I IFN cell assay Murine IFN-b production was detected in macrophage supernatants by ELISA according to the manufacturer's procedure (PBL Biomedical Laboratories). For the HEK-blue type I IFN assay, supernatant from THP-1 macrophage assays was collected and 20 mL added onto HEK-blue type I IFN cells plated in 96-well plates, which were incubated at 37uC overnight. Supernatant from HEK-blue cells was collected and 40 mL added to 160 mL of Quanti-blue reagent (Invivogen) for 20 min at 37uC. The colorimetric reaction was measured at 625 nm on a plate reader. Data was normalised against absorbance for the untreated cells and plotted as relative fold increases. Data shown are representatives of at least three independent experiments.