Fig. 1.

IFN-I induction and viral counteracting actions. Viral motifs (e.g. dsRNA), are recognized by PPRs. This leads to the activation of adaptor proteins such as NFκB, TBK-1, IKKε and AP-1. TBK-1 and IKKε phosphorylate IRF3, which translocate to the nucleus and induce IFN-I expression. In a second IFN signaling wave, IRF7 is phosphorylated and translocated to the nucleus, creating an amplification loop of IFN-I induction. Several viruses have developed mechanisms to block several steps of this IFN induction cascade, indicated in red blades in the figure