title: Critical and direct involvement of the CD23 stalk region in IgE binding.
abstract: The low-affinity receptor for IgE, FcεRII (CD23), contributes to allergic inflammation through allergen presentation to T cells, regulation of IgE responses, and enhancement of transepithelial allergen migration.
  
  
  
  We sought to investigate the interaction between CD23, chimeric monoclonal human IgE, and the corresponding birch pollen allergen Bet v 1 at a molecular level.
  
  
  
  We expressed 4 CD23 variants. One variant comprised the full extracellular portion of CD23, including the stalk and head domain; 1 variant was identical with the first, except for an amino acid exchange in the stalk region abolishing the N-linked glycosylation site; and 2 variants represented the head domain, 1 complete and 1 truncated. The 4 CD23 variants were purified as monomeric and structurally folded proteins, as demonstrated by gel filtration and circular dichroism. By using a human IgE mAb, the corresponding allergen Bet v 1, and a panel of antibodies specific for peptides spanning the CD23 surface, both binding and inhibition assays and negative stain electron microscopy were performed.
  
  
  
  A hitherto unknown IgE-binding site was mapped on the stalk region of CD23, and the non-N-glycosylated monomeric version of CD23 was superior in IgE binding compared with glycosylated CD23. Furthermore, we demonstrated that a therapeutic anti-IgE antibody, omalizumab, which inhibits IgE binding to FcεRI, also inhibited IgE binding to CD23.
  
  
  
  Our results provide a new model for the CD23-IgE interaction. We show that the stalk region of CD23 is crucially involved in IgE binding and that the interaction can be blocked by the therapeutic anti-IgE antibody omalizumab.
authors.affiliation: Department of Otorhinolaryngology, Medical University of Vienna, Vienna, Austria.
authors.forename: Regina
authors.initials: R
authors.lastname: Selb
authors.affiliation: Department of Otorhinolaryngology, Medical University of Vienna, Vienna, Austria.
authors.forename: Julia
authors.initials: J
authors.lastname: Eckl-Dorna
authors.affiliation: Division of Immunopathology, Department of Pathophysiology and Allergy Research, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Vienna, Austria.
authors.forename: Teresa E
authors.initials: TE
authors.lastname: Twaroch
authors.affiliation: Division of Immunopathology, Department of Pathophysiology and Allergy Research, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Vienna, Austria.
authors.forename: Christian
authors.initials: C
authors.lastname: Lupinek
authors.affiliation: Institute of Molecular Biosciences, Karl Franzens University, Graz, Austria.
authors.forename: Andrea
authors.initials: A
authors.lastname: Teufelberger
authors.affiliation: Institute of Molecular Biosciences, Karl Franzens University, Graz, Austria.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Hofer
authors.affiliation: Division of Immunopathology, Department of Pathophysiology and Allergy Research, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Vienna, Austria.
authors.forename: Margarete
authors.initials: M
authors.lastname: Focke-Tejkl
authors.affiliation: Division of Medical Biotechnology, Department of Pathophysiology and Allergy Research, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Vienna, Austria.
authors.forename: Barbara
authors.initials: B
authors.lastname: Gepp
authors.affiliation: Division of Immunopathology, Department of Pathophysiology and Allergy Research, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Vienna, Austria.
authors.forename: Birgit
authors.initials: B
authors.lastname: Linhart
authors.affiliation: Division of Medical Biotechnology, Department of Pathophysiology and Allergy Research, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Vienna, Austria.
authors.forename: Heimo
authors.initials: H
authors.lastname: Breiteneder
authors.affiliation: Department of Cell Biology and Ultrastructure Research, Center for Anatomy and Cell Biology, Medical University of Vienna, Vienna, Austria.
authors.forename: Adolf
authors.initials: A
authors.lastname: Ellinger
authors.affiliation: Institute of Molecular Biosciences, Karl Franzens University, Graz, Austria.
authors.forename: Walter
authors.initials: W
authors.lastname: Keller
authors.affiliation: Department of Biological Science, Florida State University, Tallahassee, Fla.
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Roux
authors.affiliation: Division of Immunopathology, Department of Pathophysiology and Allergy Research, Center for Pathophysiology, Infectiology and Immunology, Medical University of Vienna, Vienna, Austria. Electronic address: Rudolf.valenta@meduniwien.ac.at.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Valenta
authors.affiliation: Department of Otorhinolaryngology, Medical University of Vienna, Vienna, Austria.
authors.forename: Verena
authors.initials: V
authors.lastname: Niederberger
mesh_terms: D000818:Animals; D052179:Antigens, Plant / Q000276:immunology*; D001665:Binding Sites; D002460:Cell Line; D006801:Humans; D007073:Immunoglobulin E / Q000276:immunology*; D007313:Insecta; D000069444:Omalizumab / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D017455:Receptors, IgE / Q000737:chemistry / Q000276:immunology*
chemical_list: D052179:Antigens, Plant; D017455:Receptors, IgE; C061312:Bet v 1 allergen, Betula; D000069444:Omalizumab; D007073:Immunoglobulin E
keywords: B cell; CD23; IgE; allergen; allergy; low-affinity IgE receptor