Adapter protein involved in the Toll-like receptor and IL-1 receptor signaling pathway in the innate immune response. Predominantly cytoplasmic, with some expression in the nucleus. Expressed in spleen, liver, kidney, bursa of Fabricius, lung and brain (at protein level). Expressed in cecum, heart, spleen, liver, kidney, female reproductive tract, thymus, bursa of Fabricius, muscle and lung. The intermediate domain (ID) is required for the phosphorylation and activation of IRAK.