TLR3 and viral infectious disease: Type III IFN is described to not be expressed continuously but to be co-induced with type I IFNs in different cells by various human viruses, as well as by ligands of TLR3, mimicking viral infection (synthetic dsRNA; polyI:C), TLR4 (house dust mite antigen), TLR9 (unmethylated DNA rich in CpG motifs), and TLR7 and TLR8 (guanosine or uridine-rich ssRNA or resiquimod) (55, 58, 60).