There are thus two main TLR-dependent pathways for IFN-I induction during virus infections: a pathway involving TLR3-triggered, TRIF-dependent activation of IRF3, which can be utilized in TLR3-expressing cell types including macrophages and cDCs; and a pathway involving TLR7 or TLR9-triggered, MyD88-dependent activation of IRF7, which is unique to pDCs [57,97,101,104]. This evidence concerns the gene TLR3 and viral infectious disease.