Toll-like receptors (TLR) are highly conserved throughout evolution and have been implicated in the innate defence to many pathogens. In Drosophila toll is required for the anti-fungal response, while the related 18-wheeler is involved in antibacterial defences. In mammals, TLR identified as type I membrane signalling receptors with pattern recognition capabilies, have been implicated in the innate host defence to pathogens. As investigated so far all functional characterized TLR signal via the TLR/IL-1 receptor (IL-1R) pathway where recruitment of MyD88 seems to be essential. Viral replication within infected cells results in generation of dsRNA which can stimulate immune cells. Recent data show that TLR3 in viral recognition and innate defence.