title: Alternative splicing of interleukin-33 and type 2 inflammation in asthma.
abstract: Type 2 inflammation occurs in a large subgroup of asthmatics, and novel cytokine-directed therapies are being developed to treat this population. In mouse models, interleukin-33 (IL-33) activates lung resident innate lymphoid type 2 cells (ILC2s) to initiate airway type 2 inflammation. In human asthma, which is chronic and difficult to model, the role of IL-33 and the target cells responsible for persistent type 2 inflammation remain undefined. Full-length IL-33 is a nuclear protein and may function as an "alarmin" during cell death, a process that is uncommon in chronic stable asthma. We demonstrate a previously unidentified mechanism of IL-33 activity that involves alternative transcript splicing, which may operate in stable asthma. In human airway epithelial cells, alternative splicing of the IL-33 transcript is consistently present, and the deletion of exons 3 and 4 (Δ exon 3,4) confers cytoplasmic localization and facilitates extracellular secretion, while retaining signaling capacity. In nonexacerbating asthmatics, the expression of Δ exon 3,4 is strongly associated with airway type 2 inflammation, whereas full-length IL-33 is not. To further define the extracellular role of IL-33 in stable asthma, we sought to determine the cellular targets of its activity. Comprehensive flow cytometry and RNA sequencing of sputum cells suggest basophils and mast cells, not ILC2s, are the cellular sources of type 2 cytokines in chronic asthma. We conclude that IL-33 isoforms activate basophils and mast cells to drive type 2 inflammation in chronic stable asthma, and novel IL-33 inhibitors will need to block all biologically active isoforms.
authors.affiliation: Department of Pulmonary and Critical Care Medicine, University of California, San Francisco, CA 94143; erin.gordon@ucsf.edu john.fahy@ucsf.edu.
authors.forename: Erin D
authors.initials: ED
authors.lastname: Gordon
authors.affiliation: Department of Microbiology and Immunology, University of California San Francisco, CA 94143;
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Simpson
authors.affiliation: Center for Genes, Environment, and Health, National Jewish Health, Denver, CO 80206;
authors.forename: Cydney L
authors.initials: CL
authors.lastname: Rios
authors.affiliation: Center for Genes, Environment, and Health, National Jewish Health, Denver, CO 80206;
authors.forename: Lando
authors.initials: L
authors.lastname: Ringel
authors.affiliation: Cardiovascular Research Institute, University of California, San Francisco, CA 94143;
authors.forename: Marrah E
authors.identifier: 0000-0002-3173-5662
authors.initials: ME
authors.lastname: Lachowicz-Scroggins
authors.affiliation: Department of Pulmonary and Critical Care Medicine, University of California, San Francisco, CA 94143;
authors.forename: Michael C
authors.initials: MC
authors.lastname: Peters
authors.affiliation: Center for Genes, Environment, and Health, National Jewish Health, Denver, CO 80206;
authors.forename: Agata
authors.initials: A
authors.lastname: Wesolowska-Andersen
authors.affiliation: Department of Microbiology and Immunology, University of California San Francisco, CA 94143;
authors.forename: Jeanmarie R
authors.initials: JR
authors.lastname: Gonzalez
authors.affiliation: Cardiovascular Research Institute, University of California, San Francisco, CA 94143;
authors.forename: Hannah J
authors.initials: HJ
authors.lastname: MacLeod
authors.affiliation: Department of Microbiology and Immunology, University of California San Francisco, CA 94143;
authors.forename: Laura S
authors.initials: LS
authors.lastname: Christian
authors.affiliation: Cardiovascular Research Institute, University of California, San Francisco, CA 94143;
authors.forename: Shaopeng
authors.identifier: 0000-0001-9554-1325
authors.initials: S
authors.lastname: Yuan
authors.affiliation: Cardiovascular Research Institute, University of California, San Francisco, CA 94143;
authors.forename: Liam
authors.initials: L
authors.lastname: Barry
authors.affiliation: Department of Pulmonary and Critical Care Medicine, University of California, San Francisco, CA 94143; Sandler Asthma Basic Research Center, University of California, San Francisco, CA 94143;
authors.forename: Prescott G
authors.initials: PG
authors.lastname: Woodruff
authors.affiliation: Department of Microbiology and Immunology, University of California San Francisco, CA 94143; Sandler Asthma Basic Research Center, University of California, San Francisco, CA 94143;
authors.forename: K Mark
authors.initials: KM
authors.lastname: Ansel
authors.affiliation: Immunoscience, Pfizer Worldwide Research and Development, Cambridge, MA 02139;
authors.forename: Karl
authors.initials: K
authors.lastname: Nocka
authors.affiliation: Center for Genes, Environment, and Health, National Jewish Health, Denver, CO 80206; Department of Pediatrics, National Jewish Health, Denver, CO 80206; Division of Pulmonary Sciences and Critical Care Medicine, Department of Medicine, Anschutz Medical Campus, University of Colorado, Aurora, CO 80045.
authors.forename: Max A
authors.initials: MA
authors.lastname: Seibold
authors.affiliation: Department of Pulmonary and Critical Care Medicine, University of California, San Francisco, CA 94143; Cardiovascular Research Institute, University of California, San Francisco, CA 94143; Sandler Asthma Basic Research Center, University of California, San Francisco, CA 94143; erin.gordon@ucsf.edu john.fahy@ucsf.edu.
authors.forename: John V
authors.initials: JV
authors.lastname: Fahy
mesh_terms: D000328:Adult; D017398:Alternative Splicing; D001249:Asthma / Q000235:genetics* / Q000378:metabolism; D001491:Basophils / Q000378:metabolism; D002460:Cell Line; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D020869:Gene Expression Profiling / Q000379:methods; D006801:Humans; D007249:Inflammation / Q000235:genetics* / Q000378:metabolism; D000072179:Interleukin-1 Receptor-Like 1 Protein / Q000235:genetics / Q000378:metabolism; D000067596:Interleukin-33 / Q000235:genetics* / Q000378:metabolism; D008297:Male; D008407:Mast Cells / Q000378:metabolism; D008875:Middle Aged; D020545:Respiratory Mucosa / Q000378:metabolism / Q000473:pathology; D013183:Sputum / Q000166:cytology / Q000378:metabolism; D055815:Young Adult
chemical_list: C079241:IL1RL1 protein, human; D000072179:Interleukin-1 Receptor-Like 1 Protein; D000067596:Interleukin-33
keywords: alternative splicing; asthma; basophils; interleukin-33; type 2 inflammation