We note that IFN-β was not induced by exogenous IFN-α in either CEFs (at least as detected by microarray) or DF-1 cells but it was induced (to a lesser extent in DF-1 cells than in CEFs) by infection with IBDV, clearly demonstrating the requirement for a second signal (along with IRF3 activation) for induction of the IFN-β promoter. This evidence concerns the gene IFNB1 and infection.