In mammals activated IRAK4 phosphorylates both IRAK1 and IRAK2. Activated IRAK1 and IRAK2 in turn induce NFkB and AP-1 intracellular signaling cascades mediated by TRAF6.
Bioinformatic analysis reveals no evidence of IRAK1 in the chicken genome. It is possible that the chicken TLR pathway utilizes only IRAK-2, which shares 47% amino acid sequence identity with human IRAK2.
protein serine/threonine kinase activity of IRAK2 : p-IRAK4 :MyD88 : activated TLR [plasma membrane]