Toll-like receptors (TLRs) are signaling molecules that recognize different microbial products during infection and serve as an important link between the innate and adaptive immune responses. These proteins act through adaptor molecules such as MyD88 and TIRAP to activate various kinases and transcription factors. Like TLR7, TLR8 is localized to endosomal or lysosomal compartments and stimulates the innate immune response after activation by guanosine- and uridine-rich single-stranded RNA. Human but not murine TLR8 confers responsiveness to the antiviral compound R-848.