Interleukin 33 also known as IL-33 is a protein that in humans is encoded by the IL33 gene.
IL-33 is a member of the IL-1 family that potently drives production of T helper-2 (Th2)-associated cytokines (e.g., IL-4). IL33 is a ligand for IL33R (IL1RL1), an IL-1 family receptor that is selectively expressed on Th2 cells and mast cells.
Interleukin 33 (IL-33) is a cytokine belonging to the IL-1 superfamily. IL-33 induces helper T cells, mast cells, eosinophils and basophils to produce type 2 cytokines. This cytokine was previously named NF-HEV 'nuclear factor (NF) in high endothelialvenules' (HEVs) since it was originally identified in these specialized cells. IL-33 mediates its biological effects by interacting with the receptors ST2 (also known as IL1RL1) and IL-1 Receptor Accessory Protein (IL1RAP), activating intracellular molecules in the NF-κB and MAP kinase signaling pathways that drive production of type 2 cytokines (e.g. IL-5 and IL-13) from polarized Th2 cells. The induction of type 2 cytokines by IL-33 in vivo is believed to induce the severe pathological changes observed in mucosal organs following administration of IL-33.
IL-33 is a member of the IL-1 superfamily of cytokines, a determination based in part on the molecules β-trefoil structure, a conserved structure type described in other IL-1 cytokines, including IL-1α, IL-1β, IL-1Ra and IL-18. In this structure, the 12 β-strands of the β-trefoil are arranged in three pseudorepeats of four β-strand units, of which the first and last β-strands are antiparallel staves in a six-stranded β-barrel, while the second and third β-strands of each repeat form a β-hairpin sitting atop the β-barrel. IL-33 is a ligand that binds to a high-affinity receptor family member ST2. The complex of these two molecules with IL-1RAcP indicates a ternary complex formation. The binding area appears to be a mix of polar and non-polar regions that create a specific binding between ligand and receptor. The interface between the molecules has been shown to be extensive. Structural data on the IL-33 molecule was determined by solution NMR and small angle X-ray scattering.
^Schmitz J, Owyang A, Oldham E, Song Y, Murphy E, McClanahan TK, Zurawski G, Moshrefi M, Qin J, Li X, Gorman DM, Bazan JF, Kastelein RA (November 2005). "IL-33, an interleukin-1-like cytokine that signals via the IL-1 receptor-related protein ST2 and induces T helper type 2-associated cytokines". Immunity23 (5): 479–90. doi:10.1016/j.immuni.2005.09.015. PMID16286016.