| Structural highlights
Function
IL33_HUMAN Cytokine that binds to and signals through IL1RL1/ST2 and its stimulation recruits MYD88, IRAK1, IRAK4, and TRAF6, followed by phosphorylation of MAPK3/ERK1 and/or MAPK1/ERK2, MAPK14, and MAPK8. Induces T-helper type 2-associated cytokines. Acts as a chemoattractant tor Th2 cells, and may function as an "alarmin", that amplifies immune responses during tissue injury.[1] [2] [3] [4] [5] [6] [7] In quiescent endothelia the uncleaved form is constitutively and abundantly expressed, and acts as a chromatin-associated nuclear factor with transcriptional repressor properties, it may sequester nuclear NF-kappaB/RELA, lowering expression of its targets. This form is rapidely lost upon angiogenic or proinflammatory activation.[8] [9] [10] [11] [12] [13] [14]
Publication Abstract from PubMed
Interleukin-33 (IL-33), an alarmin cytokine of the IL-1 family, drives type 2 inflammation through signaling via the ST2 and IL-1RAcP receptors, making it a critical therapeutic target for inflammatory diseases such as asthma and chronic obstructive pulmonary disease. Current therapeutic strategies have primarily focused on antibodies that target IL-33 or ST2 to disrupt their specific interaction. However, the structural mechanisms underlying antibody-mediated neutralization of IL-33 remain poorly understood. Here, we report the structures of three antibodies in clinical trial - etokimab, itepekimab, and tozorakimab - complexed with IL-33, determined by X-ray crystallography and cryo-electron microscopy. Structural analysis reveals two distinct neutralizing epitopes on IL-33, termed Epitope 1 at IL-33/ST2 binding Site 1 and Epitope 2 at IL-33/ST2 binding Site 2. Tozorakimab, which targets Epitope 1, completely blocks ST2 engagement by sterically occluding the ST2 D1-D2 domain-binding interface. In contrast, etokimab and itepekimab, which recognize Epitope 2, interfere with IL-33 recognition of the ST2 D3 domain and thereby only partially inhibit ST2 binding. These structural and biochemical findings provide a molecular explanation for the differential efficacy of the three antibodies in inhibiting IL-33 signaling in cellular assays. Collectively, our results provide valuable insights into the molecular determinants of efficacy for existing IL-33 therapeutics and offer a structural framework for the rational design of next-generation IL-33 targeted inhibitors.
Structures of clinical antibodies bound to IL-33 uncover two distinct epitopes underlying differential efficacy.,Chen J, Wang Y, Wang X MAbs. 2026 Dec;18(1):2639673. doi: 10.1080/19420862.2026.2639673. Epub 2026 Mar , 1. PMID:41765683[15]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ 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. 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. Immunity. 2005 Nov;23(5):479-90. PMID:16286016 doi:S1074-7613(05)00311-0
- ↑ Komai-Koma M, Xu D, Li Y, McKenzie AN, McInnes IB, Liew FY. IL-33 is a chemoattractant for human Th2 cells. Eur J Immunol. 2007 Oct;37(10):2779-86. PMID:17853410 doi:10.1002/eji.200737547
- ↑ Carriere V, Roussel L, Ortega N, Lacorre DA, Americh L, Aguilar L, Bouche G, Girard JP. IL-33, the IL-1-like cytokine ligand for ST2 receptor, is a chromatin-associated nuclear factor in vivo. Proc Natl Acad Sci U S A. 2007 Jan 2;104(1):282-7. Epub 2006 Dec 21. PMID:17185418 doi:10.1073/pnas.0606854104
- ↑ Kuchler AM, Pollheimer J, Balogh J, Sponheim J, Manley L, Sorensen DR, De Angelis PM, Scott H, Haraldsen G. Nuclear interleukin-33 is generally expressed in resting endothelium but rapidly lost upon angiogenic or proinflammatory activation. Am J Pathol. 2008 Oct;173(4):1229-42. doi: 10.2353/ajpath.2008.080014. Epub 2008 , Sep 11. PMID:18787100 doi:10.2353/ajpath.2008.080014
- ↑ Moussion C, Ortega N, Girard JP. The IL-1-like cytokine IL-33 is constitutively expressed in the nucleus of endothelial cells and epithelial cells in vivo: a novel 'alarmin'? PLoS One. 2008 Oct 6;3(10):e3331. doi: 10.1371/journal.pone.0003331. PMID:18836528 doi:10.1371/journal.pone.0003331
- ↑ Ali S, Mohs A, Thomas M, Klare J, Ross R, Schmitz ML, Martin MU. The dual function cytokine IL-33 interacts with the transcription factor NF-kappaB to dampen NF-kappaB-stimulated gene transcription. J Immunol. 2011 Aug 15;187(4):1609-16. doi: 10.4049/jimmunol.1003080. Epub 2011, Jul 6. PMID:21734074 doi:10.4049/jimmunol.1003080
- ↑ Kakkar R, Hei H, Dobner S, Lee RT. Interleukin 33 as a mechanically responsive cytokine secreted by living cells. J Biol Chem. 2012 Feb 24;287(9):6941-8. doi: 10.1074/jbc.M111.298703. Epub 2012, Jan 3. PMID:22215666 doi:10.1074/jbc.M111.298703
- ↑ 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. 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. Immunity. 2005 Nov;23(5):479-90. PMID:16286016 doi:S1074-7613(05)00311-0
- ↑ Komai-Koma M, Xu D, Li Y, McKenzie AN, McInnes IB, Liew FY. IL-33 is a chemoattractant for human Th2 cells. Eur J Immunol. 2007 Oct;37(10):2779-86. PMID:17853410 doi:10.1002/eji.200737547
- ↑ Carriere V, Roussel L, Ortega N, Lacorre DA, Americh L, Aguilar L, Bouche G, Girard JP. IL-33, the IL-1-like cytokine ligand for ST2 receptor, is a chromatin-associated nuclear factor in vivo. Proc Natl Acad Sci U S A. 2007 Jan 2;104(1):282-7. Epub 2006 Dec 21. PMID:17185418 doi:10.1073/pnas.0606854104
- ↑ Kuchler AM, Pollheimer J, Balogh J, Sponheim J, Manley L, Sorensen DR, De Angelis PM, Scott H, Haraldsen G. Nuclear interleukin-33 is generally expressed in resting endothelium but rapidly lost upon angiogenic or proinflammatory activation. Am J Pathol. 2008 Oct;173(4):1229-42. doi: 10.2353/ajpath.2008.080014. Epub 2008 , Sep 11. PMID:18787100 doi:10.2353/ajpath.2008.080014
- ↑ Moussion C, Ortega N, Girard JP. The IL-1-like cytokine IL-33 is constitutively expressed in the nucleus of endothelial cells and epithelial cells in vivo: a novel 'alarmin'? PLoS One. 2008 Oct 6;3(10):e3331. doi: 10.1371/journal.pone.0003331. PMID:18836528 doi:10.1371/journal.pone.0003331
- ↑ Ali S, Mohs A, Thomas M, Klare J, Ross R, Schmitz ML, Martin MU. The dual function cytokine IL-33 interacts with the transcription factor NF-kappaB to dampen NF-kappaB-stimulated gene transcription. J Immunol. 2011 Aug 15;187(4):1609-16. doi: 10.4049/jimmunol.1003080. Epub 2011, Jul 6. PMID:21734074 doi:10.4049/jimmunol.1003080
- ↑ Kakkar R, Hei H, Dobner S, Lee RT. Interleukin 33 as a mechanically responsive cytokine secreted by living cells. J Biol Chem. 2012 Feb 24;287(9):6941-8. doi: 10.1074/jbc.M111.298703. Epub 2012, Jan 3. PMID:22215666 doi:10.1074/jbc.M111.298703
- ↑ Chen J, Wang Y, Wang X. Structures of clinical antibodies bound to IL-33 uncover two distinct epitopes underlying differential efficacy. MAbs. 2026 Dec;18(1):2639673. PMID:41765683 doi:10.1080/19420862.2026.2639673
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