Nitration of the Pollen Allergen Bet v 1.0101 Enhances the Presentation of Bet v 1-Derived Peptides by HLA-DR on Human Dendritic Cells

Nitration of pollen derived allergens can occur by NO2 and ozone in polluted air and it has already been shown that nitrated major birch (Betula verrucosa) pollen allergen Bet v 1.0101 (Bet v 1) exhibits an increased potency to trigger an immune response. However, the mechanisms by which nitration might contribute to the induction of allergy are still unknown. In this study, we assessed the effect of chemically induced nitration of Bet v 1 on the generation of HLA-DR associated peptides. Human dendritic cells were loaded with unmodified Bet v 1 or nitrated Bet v 1, and the naturally processed HLA-DR associated peptides were subsequently identified by liquid chromatography-mass spectrometry. Nitration of Bet v 1 resulted in enhanced presentation of allergen-derived HLA-DR-associated peptides. Both the copy number of Bet v 1 derived peptides as well as the number of nested clusters was increased. Our study shows that nitration of Bet v 1 alters antigen processing and presentation via HLA-DR, by enhancing both the quality and the quantity of the Bet v 1-specific peptide repertoire. These findings indicate that air pollution can contribute to allergic diseases and might also shed light on the analogous events concerning the nitration of self-proteins

Nitration of Bet v 1 increases the copy number of identified allergen-derived peptides with identical amino acid sequence.

<p>The numbers of detected copies of allergen derived peptides with identical peptide sequence, derived from DCs loaded with unmodified Bet v 1 (grey bars) and allergen derived peptides derived from DCs loaded with Bet v 1 nitro (black bars) are shown for each identical peptide and corresponding donors. Due to the limited amount of available cells for peptide isolation, each sample was measured only once.</p

Structural analysis of the tyrosine residues in Bet v 1.0101.

<p>(A) Cartoon representation with alpha-helices in magenta and beta-strands in yellow. The tyrosine residues are shown as sticks. (B) Electrostatic potential mapped to the protein surface. Positive charges are colored blue and negative charges are colored red. The tyrosine residues are show as spheres, the CH groups are show in green color. (C) The front half of Bet v 1 is cut off providing a view to the large central cavity. Tyrosines Y81 and Y83 are exposed to the cavity. The figure was prepared with UCSF Chimera <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031483#pone.0031483-Pettersen1" target="_blank">[34]</a>.</p