The interplay between tree pollen allergens and their source

Background: Presently, it is still unclear which molecular properties distinguish allergenic from non-allergenic or strong from weak sensitizing proteins in a given allergen source. Highly homologous allergens (e.g. birch Bet v 1 and chestnut Cas s 1), both expressed at high levels in the respective pollen, show striking differences concerning their allergenicity in humans. While pollen grains themselves have been shown to function as carriers for allergens and other bioactive allergy-promoting substances, very few studies have focused on the interactions between them. We hypothesized that interactions between allergens and compounds in their source have a strong influence on the ensuing immune response to allergens. Goals: The primary goal of this project is to shed light on the interactions between strong- and weak- sensitizing pollen allergens with their respective sources and to investigate how these interactions influence the allergic sensitization. We will focus on the analyses of the immunological effects resulting from interactions between selected allergenic and low/non-allergenic molecules with allergenic and low/non allergenic pollen sources, as well as with defined adjuvants and ligands, on the allergic sensitization process. Methods: Extracts of allergenic and non-allergenic pollen will be dissected into different components/fractions (protein, low molecular weight components, lipids, etc.). To mimic the human exposure, nasal fluids collected from allergic as well as non-allergic donors will be used as solvents for investigating the release of pollen allergens and other compounds. Extract fractions will be characterized by proteomics and metabolomics, respectively. Pollen-derived fractions will be combined with model allergens from different sources and the effects on protein stability (e.g. susceptibility to proteolysis, thermal denaturation), antibody- and ligand- binding activity will be analyzed. Antigen uptake and presentation will be studied with dendritic cells. The possible role of innate immune receptors on the allergen/pollen compound-DC interactions will be addressed using PRR-neutralizing antibodies or PRR-specific inhibitors. Internalization will be investigated using selective inhibitors of antigen uptake. Proteome and transcriptome analyses of activated and FACS-sorted DCs will be performed. To study matrix effects on model allergens/molecules in vivo, we will initially perform a screening for their TH2 polarizing potential using the G4/IL4 transgenic mouse. The most relevant molecule/fraction combinations will be further investigated using models of adjuvant-free allergic sensitization (subcutaneous, intranasal, transcutaneous) and the humoral and cellular immune responses analyzed. Expected Outcomes: The work in this project will dissect the adjuvant and modulatory effects of pollen-derived components on allergens, elucidate the mechanisms by which such interactions induce immune polarization, and thus help to define pathways leading to sensitization in allergy.

Allergies to pollen are the most frequent type of allergy with an estimated prevalence of 40% among patients suffering from respiratory allergies, which affect 100 million Europeans. Pollen allergens are also considered a major risk factor for both, seasonal allergic rhinitis and bronchial asthma, affecting 20% and 8% of the general population, respectively. This project aimed to shed light on the interactions between pollen allergens with their respective sources and to investigate how these interactions influence the process of allergic sensitization. Our findings supported the notion that sensitization is not exclusively linked to the intrinsic properties of individual pollen allergens, but seems to result from complex interactions between allergenic molecules, the "pollen matrix", which consists of a complex mixture of different compounds, and the host immune cells. Our results showed that certain non-allergenic compounds found in the "pollen matrix" can directly interact with receptors in the host immune cells and co-deliver polarizing signals for allergy development. The project's findings have important consequences for the assessment of mechanisms in allergic sensitization and therapeutic approaches.