IFNB1 and infection: To determine which cell population(s) are the major producer(s) of IFN-β upon VACV∆C7L infection, IFN-β-yellow fluorescent protein (YFP) reporter mice (Ifnb1Eyfp) were used to map the cell type(s) responsible for IFN-β production induced by VACV∆C7L infection.