Fig. 1.

Intracellular signaling pathways of pattern-recognition receptors. TLRs are mostly present on the membrane. RLRs and NLRs are located in the cytosol. TLRs send signal through Mal/TIRAP and MyD88 or TRAM/TRIF to IRAK/TRAF6 to activate downstream kinases. RLRs use IPS-1 and TRAF3 as adaptor molecules and NLRs transmit activation signals through TRAF6. The signals from TLRs, RLRs, and NLRs are delivered to kinases such as MAPKs, IKKs, TBK1, RIP-1, and RICK to activate transcription factor, AP-1, NF-κB, and IRF. Transcription factors bind to specific DNA sequences and produce effecter molecules such as cytokines, inflammatory enzymes, chemokines, and type I interferons (IFNs).