TLR7 and viral infectious disease: Ligation of host pattern-recognition receptors, such as the cytoplasmic helicase RIG-I family and TLR3, TLR7, and TLR9, triggers activation of the transcription factor interferon regulatory factor 7, which translocates to the nucleus, where it promotes IFN-I production.37,51 IFN-Is are normally induced at early time points after viral infection and are therefore critical for control of replication and establishment of a definitive immunologic clearance.