title: Abrogation of allergic reactions by a bispecific antibody fragment linking IgE to CD300a.
abstract: BACKGROUND
  Initiated and regulated by mast cells, allergic responses are balanced through an intricate network of positive and negative signals. We have recently shown that the inhibitory receptor CD300a is expressed on human mast cells and modulates a large array of their functions.
  
  
  OBJECTIVE
  We sought to evaluate CD300a as a negative regulator of allergic inflammation in vivo by means of a bispecific antibody linking CD300a with IgE.
  
  
  METHODS
  Bispecific antibody fragments were generated by chemical conjugation of Fab' fragments of anti-human IgE and CD300a (IE1H) and anti-mouse IgE and CD300a (IE1M). IgE-sensitized human mast cells were activated simultaneously with anti-IgE and IE1H. Phosphorylation of signaling proteins and calcium influx were evaluated by using fluorescence-activated cell sorting. Degranulation was assessed on the basis of tryptase and IL-4 release. IE1M was administered simultaneously with allergen challenge in 2 murine models of allergic disease. Passive cutaneous anaphylaxis was assessed by means of dye exudation. Experimental airway inflammation was assessed on the basis of tryptase and cytokine content, eosinophilic infiltration, and lung histology (hematoxylin and eosin and periodic acid-Schiff stain).
  
  
  RESULTS
  IE1H potently inhibited IgE-mediated mast cell degranulation in a dose-dependent manner by inhibiting the signaling events induced by FcvarepsilonRI. IE1M completely abolished dye exudation in passive cutaneous anaphylaxis. IE1M abrogated allergic airway inflammation.
  
  
  CONCLUSIONS
  Our results demonstrate that specific targeting of CD300a on mast cells is a potent strategy for inhibiting allergic reactions.
  
  
  CONCLUSIONS
  This work demonstrates a potent approach for the therapy of allergic diseases.
authors.affiliation: Department of Pharmacology, School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Israel.
authors.forename: Ido
authors.initials: I
authors.lastname: Bachelet
authors.forename: Ariel
authors.initials: A
authors.lastname: Munitz
authors.forename: Francesca
authors.initials: F
authors.lastname: Levi-Schaffer
mesh_terms: D000818:Animals; D018033:Antibodies, Bispecific / Q000378:metabolism* / Q000494:pharmacology*; D015703:Antigens, CD; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D006967:Hypersensitivity / Q000276:immunology* / Q000517:prevention & control*; D007073:Immunoglobulin E / Q000276:immunology* / Q000378:metabolism; D007140:Immunoglobulin Fab Fragments / Q000378:metabolism / Q000627:therapeutic use*; D008407:Mast Cells / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D011971:Receptors, Immunologic / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D054340:Receptors, KIR
chemical_list: D018033:Antibodies, Bispecific; D015703:Antigens, CD; C515070:CD300A protein, human; D007140:Immunoglobulin Fab Fragments; D011971:Receptors, Immunologic; D054340:Receptors, KIR; D007073:Immunoglobulin E