Critical and direct involvement of the CD23 stalk region in IgE binding

• Published in: Journal of allergy and clinical immunology 2017-01, Vol.139 (1), p.281-289.e5
• Main Authors: Selb, Regina, PhD, Eckl-Dorna, Julia, MD, PhD, Twaroch, Teresa E., PhD, Lupinek, Christian, MD, Teufelberger, Andrea, MSc, Hofer, Gerhard, MSc, Focke-Tejkl, Margarete, PhD, Gepp, Barbara, PhD, Linhart, Birgit, PhD, Breiteneder, Heimo, PhD, Ellinger, Adolf, MD, Keller, Walter, PhD, Roux, Kenneth H., PhD, Valenta, Rudolf, MD, Niederberger, Verena, MD
• Format: Article
• Language: English
• Subjects: allergen; allergy; Allergy and Immunology; Amino acids; Animals; Antigens, Plant - immunology; Binding Sites; B cell; CD23; Cell Line; Experiments; Humans; IgE; Immunoglobulin E - immunology; Immunoglobulins; Insecta; low-affinity IgE receptor; Microscopy; Omalizumab - pharmacology; Peptides; Protein Binding - drug effects; Proteins; Receptors, IgE - chemistry; Receptors, IgE - immunology; Statistical analysis
• ISSN: 0091-6749; 1097-6825
• DOI: 10.1016/j.jaci.2016.04.015

Background 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. Objective 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. Methods 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. Results 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. Conclusion 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.