Mechanisms underlying induction of allergic sensitization by Pru p 3

Abstract

Background Recently, the nature of the lipid-ligand of Pru p 3, one of the most common plant food allergens in Southern Europe, has been identified as a derivative of the alkaloid camptothecin bound to phytosphingosine. However, the origin of its immunological activity is still unknown. Objective We sought to evaluate the role of the Pru p 3 lipid-ligand in the immunogenic activity of Pru p 3. Methods In vitro cultures of different cell types (monocyte-derived dendritic cells (moDCs), PBMCs and epithelial and iNKT-hybridoma cell lines) have been used to determine the immunological capacity of the ligand, by measuring cell proliferation, maturation markers and cytokine production. To study the capacity of the lipid-ligand to promote sensitization to Pru p 3 in vivo, a mouse model of anaphylaxis to peach has been produced and changes in the humoral and basophil responses have been analyzed. Results The lipid-ligand of Pru p 3 induced maturation of moDCsc and proliferation of PBMCs. Its immunological activity resided in the phytosphingosine tail of the ligand. The adjuvant activity of the ligand was also confirmed in vivo, where the complex of Pru p 3-ligand induced higher levels of IgE than Pru p 3 alone. The immunological capacity of the Pru p 3 ligand was mediated by CD1d, as maturation of moDCs was inhibited by anti-CD1d antibodies and Pru p 3-ligand co-localized with CD1d on epithelial cells. Finally, Pru p 3-ligand presented by CD1d was able to interact with iNKTs. Conclusions & Clinical Relevance The Pru p 3 lipid-ligand could act as an adjuvant to promote sensitization to Pru p 3, through its recognition by CD1d receptors. This intrinsic adjuvant activity of the accompanying lipid cargo could be a general essential feature of the mechanism underlying the phenomenon of allergenicity.

Dynamic plasticity of the lipid antigen-binding site of CD1d is crucially favoured by acidic pH and helper proteins

“…Finally, the inclusion of the natural lipid ligand of Pru p 3 in our study obeys the reported experimental evidence that it (i) acts as an adjuvant promoting sensitisation to the allergen through its recognition by CD1d, (ii) is able to interact with iNKT cells upon CD1d presentation and (iii) its immunological activity resides in the PHS tail 31 . However, MD calculations do not predict a stable CD1d-Pru p 3-ligPp3 complex irrespective of pH, suggesting that although the allergen is an LTP, it is unlikely that its ligand would be loaded onto CD1d through a direct interaction with Pru p 3.…”

“…The initial geometries of the lipid ligands were taken from their complexes with CD1d (α-GalCer) and GM2AP (LPC, PC, and OLA) referenced in the main text except for PHS and ligPp3 whose geometries were taken from the MD final structures of their complexes with Pru p 3 28,31,43 . The initial structure of the peach Pru p 3 allergen was taken from its crystal structure (chain A in PDB id 2ALG 46 ).…”

“…Our work involves the calculation of molecular properties, Poisson-Boltzmann electrostatic potentials (PBEPs), electric fields as well as all-atom MD simulations. The reason for including the peach allergen Pru p 3 (prototype of plant nonspecific LTPs, the most prevalent food allergen in Mediterranean countries and a model of food allergy 29,30 ) is our recent experimental report showing that binding of a natural lipid ligand 28 to Pru p 3 provokes allergic sensitisation by CD1d-mediated activation of iNKT cells 31 . This ligand is composed of 10-hydroxy-camptothecin linked to a lipidic PHS tail 28 and is presented by CD1d to iNKT cells acting as an adjuvant to promote IgE sensitization to Pru p 3 31 .…”

Rational Design, Structure–Activity Relationship, and Immunogenicity of Hypoallergenic Pru p 3 Variants

“…Pru p 3 is considered the primary sensitizer for most patients and a positive correlation between Pru p 3 IgE‐levels and the number of LTP plant‐food causing allergic symptoms was demonstrated . A recent study suggested the relevance of the natural Pru p 3‐lipid ligand to act as adjuvant for allergic sensitization …”

Glycolipid-mediated basophil activation in alpha-gal allergy

“…2 Thus, we hypothesized that glycolipid could activate allergic effector cells in alpha-gal allergy. A role for lipids in enhancing allergenic potency has been described in peach 3 and cow's milk allergies. 4 We now demonstrate that alpha-gal sIgE binds mammalian glycolipids and that alpha-gal-containing glycolipids can activate basophils sensitized with alpha-gal sIgE, highlighting a potential role for glycolipid in alpha-gal meat allergy.…”