Interleukin-1 receptor-associated kinase (IRAK) was first described as a signal transduction agent of the pro-inflammatory cytokine IL-1, and has since been implicated in signal transduction of other members of the Toll-like receptor (TLR)/IL-1R family. Four distinct IRAK-like molecules have been identified: two active kinases, IRAK-1 and IRAK-4, and two inactive kinases, IRAK-2 and IRak-M. All IRAKS mediate activation of NF-κB and MAPK pathways. IRAK is a protein kinase involved in the innate immune response to TLR. After TLR-4 and TLR-2 recognize pathogen-associated molecular patterns, such as LPS and peptidoglycans, all IRAK members form polymeric receptor complexes. IRAK is an essential signal transduction intermediate for activation of IKK and MAPK in the TLR/IL-1R pathway. Both pathways are critical for the activation of several transcription factors, including NF-κB and AP-1, which help establish an immune response.