Toll-like receptors (TLRs) are evolutionarily conserved pattern-recognition molecules resembling the toll proteins that mediate antimicrobial responses in Drosophila. These proteins recognize different microbial products during infection and serve as an important link between the innate and adaptive immune responses. The TLRs act through adaptor molecules such as MyD88 and TIRAP to activate various kinases and transcription factors so the organism can respond to potential infection. TLR3 is known to recognize viral double-stranded (ds) RNA, a molecular pattern associated with viral infection. Recently it has been shown to recognize viruses such as Influenza A and West Nile Virus and can mediate entry of at least West Nile Virus.