IFNB1 and infection: This tardiness in type I IFN feed-forward signaling has negative consequences for host antiviral immunity: RelA-deficient embryo fibroblasts are very susceptible to interferon-sensitive RNA viruses such as vesicular stomatitis virus (Rhabdoviridae), Newcastle disease virus, and Sendai virus (both Paramyxoviridae), despite producing copious amounts of IFN-β later during the course of infection [16], [19].