title: A hypoallergenic variant of the major birch pollen allergen shows distinct characteristics in antigen processing and T-cell activation.
abstract: BACKGROUND
  BM4 is a novel genetically engineered variant of the major birch pollen allergen Bet v 1 that lacks the typical Bet v 1-like fold and displays negligible IgE-binding but strong T cell-activating capacity. The aim of this study was to elucidate possible differences between BM4 and Bet v 1 in internalization, antigen processing, and presentation.
  
  
  METHODS
  Proliferative responses to BM4 and Bet v 1 of peripheral blood mononuclear cells and Bet v 1-specific T-cell clones were compared. Fluorescently labeled BM4 and Bet v 1 were used to study surface binding, endocytosis, and intracellular degradation by monocyte-derived DC (mdDC). Both proteins were digested by endolysosomal extracts of mdDC. BM4- and Bet v 1-pulsed mdDC were employed to assess the kinetics of activation of Bet v 1-specific T-cell clones and the polarization of naïve T cells.
  
  
  RESULTS
  BM4 displayed a significantly stronger T cell-activating capacity than Bet v 1. Furthermore, BM4 showed increased surface binding and internalization as well as faster endolysosomal degradation compared with Bet v 1. BM4-pulsed mdDC induced enhanced proliferative responses at earlier time-points in Bet v 1-specific T-cell clones and promoted less IL-5 production in T cells than Bet v 1-pulsed mdDC.
  
  
  CONCLUSIONS
  The loss of the Bet v 1-fold changes the protein's interaction with the human immune system at the level of antigen-presenting cells resulting in altered T-cell responses. By combining low IgE-binding with strong and modulating T cell-activating capacity, BM4 represents a highly interesting candidate for specific immunotherapy of birch pollen allergy.
authors.affiliation: Department of Pathophysiology and Allergy Research, Christian Doppler Laboratory for Immunomodulation, Medical University of Vienna, Vienna, Austria.
authors.forename: C
authors.initials: C
authors.lastname: Kitzmüller
authors.forename: M
authors.initials: M
authors.lastname: Wallner
authors.forename: S
authors.initials: S
authors.lastname: Deifl
authors.forename: S
authors.initials: S
authors.lastname: Mutschlechner
authors.forename: C
authors.initials: C
authors.lastname: Walterskirchen
authors.forename: G J
authors.initials: GJ
authors.lastname: Zlabinger
authors.forename: F
authors.initials: F
authors.lastname: Ferreira
authors.forename: B
authors.initials: B
authors.lastname: Bohle
mesh_terms: D000485:Allergens / Q000276:immunology*; D000595:Amino Acid Sequence; D017951:Antigen Presentation; D052179:Antigens, Plant / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D029662:Betula / Q000276:immunology*; D016764:Cell Polarity; D006801:Humans; D008213:Lymphocyte Activation; D008969:Molecular Sequence Data; D011058:Pollen / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D000485:Allergens; D052179:Antigens, Plant; C061312:Bet v 1 allergen, Betula