The IL1 receptor accessory protein is responsible for the recruitment of the interleukin-1 receptor associated kinase to the IL1/IL1 receptor I complex.

Following interleukin-1 (IL1) stimulation, an IL1 receptor associated kinase (IRAK) is rapidly recruited to the receptor complex. However, it is not understood if IRAK is able to interact directly with the intracellular portion of the IL1-RI or if its recruitment is mediated by a different molecule. Using the yeast two-hybrid system, we have analysed possible protein-protein interactions between IRAK, IL1-RI and IL1-RAcP. We found that IRAK is able to interact with the equivalent cytoplasmic region of the IL1-RAcP but is unable to interact with the cytoplasmic region of the IL1-RI. Immunoprecipitation of the IL1-RAcP followed by Western blot analysis using anti-IRAK antibodies revealed that IRAK co-precipitated with the IL1-RAcP. We propose that, in non-stimulated cells, IRAK is bound to the IL1-RAcP and therefore, following IL1 stimulation, both molecules are recruited simultaneously to the ILI-RI complex.