Figure 1. Recognition of viral infection by pattern recognition receptors leads to interferon production.

Viral recognition leads to interferon induction via three principal pathways that are characterized by the adaptor proteins used to connect the upstream pattern recognition receptors with the downstream signaling machinery. Signaling via those pathways is orchestrated by the adaptor proteins STING, MAVS and either TRIF or MyD88. All the three pathways activate the kinase TBK1, which in turn phosphorylates the transcription factors IRF3 and IRF7. Notably, IRF7 is constitutively expressed in pDCs but needs to be induced by IFN signaling in other cells. In addition, these pathways also activate the NF–κB family of transcription factors, yet the molecular mechanism behind this activation remains poorly characterized.