Anti-Interleukin 33 antibodies are used in the immunodetection of the protein encoded by the IL33 gene. In humans, the canonical protein has a reported length of 270 amino acid residues and a mass of 30.8 kDa. Its subcellular localization is in the nucleus, cytoplasmic vesicles, cytoplasm, and is also secreted. Alternative splicing is reported to yield 4 different isoforms for this protein. It is notably expressed at high level in high endothelial venules found in tonsils, Peyer patches and mesenteric lymph nodes. A member of the IL-1 protein family, it is a reported to be a cytokine that binds to and signals through the IL1RL1/ST2 receptor which in turn activates NF-kappa-B and MAPK signaling pathways in target cells. Post-translational modifications have been described, including protein cleavage. Other names for this target antigen include interleukin-1 family member 11, nuclear factor for high endothelial venules, nuclear factor from high endothelial venules, and DVS27-related protein.