IFNB1 and infection: To further establish the importance of the efficient packaging of antigenomic S RNA for the suppression of the early induction of type I IFN after infection, we infected type I IFN-competent MRC-5 cells (Terasaki et al., 2011) with RVFV, RVFV Δ19 or RVFV-rLuc and examined the induction of IFN-β mRNA from 3 to 5 h p.i. (Figure 6).