IFN-a and -b were measured in sera using a biological assay as previously described [65] . Briefly, L929 cells were seeded at 3610 4 cells/well in a 96 well plate one day prior to the addition of interferon standards or experimental samples. Mouse sera (diluted 1:10 in L929 media) were treated with UV light for 20 minutes to eliminate residual virus. Duplicate sera samples were then added to the 96-well plates in two-fold dilutions along with a murine IFNb standard. The following day, EMCV challenge virus was added to the cells in 50 ml/well at an MOI of 5.0. Twenty-four hours later, cytopathic effect was measured by a blinded scorer and IFN levels in the sera was calculated based on the IFN standard. IFN-b in cell culture supernatants was analyzed using mouse-specific ELISA kits from PBL Biomedical Laboratories according to the manufacturer's protocol.