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There are two types of interleukin 1 (IL-1) receptor, of which type I (IL-1RI) is by far the most abundant. IL-1RI binds both IL-1α and IL-1β, as well as the interleukin 1 receptor antagonist IL-1RA. The latter is a naturally occurring inhibitor of IL-1 signaling.
IL-1 binding induces a conformational change in IL-1RI, which then associates the IL-1 receptor accessory protein (IL-1RAcP). This trimer features a Toll-like domain on the cytoplasmic side of the cell membrane, which is recognized by Toll-interacting protein (TOLLIP) and interleukin-1 receptor-activated protein kinase (IRAK) complexes. The IL-1:IL-1RI:IL-1RAcP trimer also recruits myeloid differentiation primary response gene 88 (MyD88), which induces IRAK autophosphorylation, dissociating it from TOLLIP and the receptor complex. Phosphorylated IRAK family members facilitate the oligomerization of tumor necrosis factor-associated factor 6 (TRAF6), which results in the eventual activation of the NF-κB, JNK, and p38 pathways.