Mammalian IRAK-4 is the homolog of Drosophila melanogaster Pelle. Like Pelle and unlike the other mammalian IRAKs, IRAK-4 is considered to be a central TIR signalling mediator in innate immunity. Mutagenesis analysis showed that any interference with IRAK-4's kinase activity virtually abolished downstream events. This is not the case with other members of the IRAK family.

Formation of MyD88:IRAKs multimer relies on homotypic interactions of death domains (DD). It triggers a cascade of phosphorylation reactions that leads to activation of NF-kB/AP-1 and transcription of multiple genes involved in the immune response.

The predicted chicken full-length IRAK-4 protein contains 414aa and is 58% identical to human IRAK-4. Chicken IRAK-4 contains a conserved N-terminal death domain and C-terminal protein kinase domain.