Two forms of interleukin-1, designated IL-1α and IL-1β, have been described. IL-1β is a pro-inflammatory cytokine produced predominantly by activated monocytes and epithelial cells. Precursor IL-1β is cleaved by caspase-1 and mature IL-1β is then secreted. Signaling by IL-1β involves IL-1β binding to IL-1 accessory protein (IL-1-AcP) and then the complex binds to IL-1RI. ignaling is through activation of MAP kinase and NF-κB pathways. IL-1β also binds to IL-1RII that lacks an intracellular signaling domain and thereby serves as a high affinity decoy receptor. IL-1β binding to IL-1RI is inhibited by the negative regulator, IL-1R antagonist (IL-1Ra).
