Multiple roles of Bet v 1 ligands in allergen stabilization and modulation of endosomal protease activity

Abstract

Background: Over 100 million people worldwide suffer from birch pollen allergy. Bet v 1 has been identified as the major birch pollen allergen. However, the molecular mechanisms of birch allergic sensitization, including the roles of Bet v 1 and other components of the birch pollen extract, remain incompletely understood. Here, we examined how known birch pollen-derived molecules influence the endolysosomal processing of Bet v 1, thereby shaping its allergenicity. Methods: We analyzed the biochemical and immunological interaction of ligandswith Bet v 1. We then investigated the proteolytic processing of Bet v 1 by endosomal extracts in the presence and absence of ligands, followed by a detailed kinetic analysis of Bet v 1 processing by individual endolysosomal proteases as well as the T-cell epitope presentation in BMDCs. Results:We identified E 1 phytoprostanes as novel Bet v 1 ligands. Pollen-derived ligands enhanced the proteolytic resistance of Bet v 1, affecting degradation kinetics and preferential cleavage sites of the endolysosomal proteases cathepsin S and legumain. E 1 phytoprostanes exhibited a dual role by stabilizing Bet v 1 and inhibiting cathepsin protease activity. Conclusion:Bet v 1 can serve as a transporter of pollen-derived, bioactive compounds. When carried to the endolysosome, such compounds can modulate the proteolytic activity, including its processing by cysteine cathepsins. We unveil a paradigm shift from an allergen-centered view to a more systemic view that includes the host endolysosomal enzymes.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

In vivo Induction of Functional Inhibitory IgG Antibodies by a Hypoallergenic Bet v 1 Variant

“…However, further experiments are needed in order to clearly state, which rat IgG subclass is responsible for the IgE blocking activity. Also, additional in vitro approaches addressing the functionality of the induced IgG antibodies in other functions of effector cells, such as the basophil activation test or mediator release assays, would provide further insights on the inhibitory capacity of the BM4-induced IgG antibodies (27,44). In a therapeutic in vivo model, increased Bet v 1-specific IgG1 levels induced by intraperitoneal injections of BM4 were associated with a downregulation in Bet v 1-triggered mediator release using rat basophilic leukemia cells, as well as a general decrease of Th2-mediated inflammation as judged by BALF IL5 cytokine secretion and lung infiltrating cells (20).…”

“…Both BM4 and placebo were formulated using aluminum hydroxide (Alu-Gel-S, Serva, Heidelberg, Germany). Expression, purification, physicochemical characterization, and determination of endotoxin contamination (<0.3 ng/mL) of recombinant Bet v 1.0101, Mal d 1.0108, and Cor a 1.0401 (called Bet v 1, Mal d 1, and Cor a 1 in the following) were performed as previously described (27,28). A representative SDS-PAGE image showing the different recombinant proteins can be found in Supplementary Figure S1.…”

Initiating pollen sensitization – complex source, complex mechanisms

“…Gilles et al demonstrated that the low-molecular weight fraction of aqueous pollen extracts induced the expression of Th2-associated notch ligands on DCs [95]. PPE1 was also shown to bind with high affinity to Bet v 1 and to inhibit endolysosomal cathepsin proteases, thus interfering with the antigen-processing machinery in APCs and modulating antigen presentation to T cells [120]. Adenosine has been identified in pollen as a metabolite and immunomodulator with dual properties.…”

“…It is possible that the amounts and stability of proteins are important requirements for a pollen protein to become a major allergen. In this respect, Bet v 1 is the most abundant protein (10–30% of total proteins) in BPE [94 ] and its thermal‐ and proteolytic‐ stability shown to be modulated by intrinsic pollen compounds [120 ]. In keeping with this view, allergens would then serve as secondary Th2 targets, i.e.…”

Advances and novel developments in molecular allergology

“…The tetrameric Alt a 1 holo‐form underwent receptor‐mediated endocytosis, activating the airway mucosa, while the dimeric apo‐form did not. A novel Bet v 1 ligand, phytoprostane E 1, was shown to inhibit the catalytic activity of cathepsin S, a cysteine protease expressed by antigen‐presenting cells, thereby protecting the allergen from degradation 34 . nsLTPs, including Pru p 3, 35 Mal d 3, and Cor a 8, were shown to undergo conformational changes when bound to lipid ligands, which increased their IgE recognition 36 …”