Dissecting specific signaling pathways induced by Bet v 1

The ability of the immune system to fight helminth infections with IgE antibodies is indispensable for life. However, the production of IgE also occurs in a maladaptive immune response to otherwise innocuous, non- pathogenic proteins, so-called allergens. In genetically predisposed individuals, the contact with allergens provokes epithelial and dendritic cells to generate a Th2-skewed cytokine environment resulting in the induction of allergen- specific IgE instead of tolerance/ignorance. We are just beginning to understand the exact nature of allergen recognition by the innate immune cells and the specific set of receptors involved. Several lines of evidence suggest that allergen recognition and uptake are selective processes directly engaging pattern recognition receptors expressed on both epithelial and dendritic cells that can drive Th2 immunity. The unresolved key questions in allergen research are (1) Why does only a limited number of proteins drive the initiation of a Th2-polarized allergic immune response and (2) why only in certain individuals? (3) What structures and correspondingly (4) what signaling mechanisms are involved that translate the innate immune recognition of these proteins into a Th2-biased immune response? To address these questions, we have selected the major birch pollen allergen (BP) Bet v 1 and three structural homologues of Bet v 1 from pathogenic and non-pathogenic bacteria. We will study the interactions of these proteins with human epithelial cell lines as well as primary human epithelial cells derived from BP allergic and normal donors. The major aims of this project will be the definition of a gene signature associated with allergic sensitization to Bet v 1 and the identification of a potential receptor expressed by epithelial cells that specifically recognizes Bet v 1 and Bet v 1-related molecules. We will employ an innovative systems biology approach that integrates different types of omics data: (1) to generate a set of candidate genes modulated by Bet v 1-related proteins by combining data sets from a real-time PCR based gene expression approach and multiplexed protein expression analysis; (2) to reconstruct a genetic network with the set of candidate genes; (3) to identify activated signaling pathways and associated signaling complexes and receptors; (4) to validate the regulatory relationships between the genes in the network by perturbing the network using siRNAs and monitoring the response using real- time PCR analysis; and (5) to identify candidate receptors for binding and internalization of Bet v 1-related proteins by label transfer protein interaction analysis. The established algorithm within the current study will allow differentiating the normal response from an allergic epithelial immune response to Bet v 1. The outcome of this project will be relevant both for basic research in allergology and for allergy diagnostics. Elucidation of the target structure responsible for binding Bet v 1 and Bet v 1-induced signaling will complement the knowledge on allergen-innate immune cell interactions. Thus we are not only exploring a new perspective on the pathogenesis of allergic diseases on the molecular level but also new starting points for the design of allergy vaccines.

Type 2 allergic diseases of the airways such as allergic asthma continue to plague modernized societies worldwide. Other than trigger avoidance, current therapies for allergic asthma comprise symptom-relieving pharmacological treatments targeting end-organ manifestations and allergen-specific immunotherapy with the objective of re-balancing the underlying immune deviation. However in many cases, the disease remains uncontrolled, highlighting the urgent need for discovery of novel therapeutic modalities. Extensive research efforts have been focused to define structural and/or functional features that render certain proteins allergenic. However, so far there is no unifying framework to explain their allergenicity. In fact, apart from genetic variants impacting on allergen-presentation and T cell recognition, there is increasing evidence that allergic sensitization rather occurs when the hosts innate sensitivity is dysregulated/imbalanced. Being the earliest line of defense, respiratory epithelial cells (ECs) play a fundamental role in setting the systemic tone of both innate and adaptive immune responses in the airways. Although the exact events are not well understood, recent studies suggest that IL-33, an alarmin strongly induced in the lungs of asthmatic individuals in response to allergens, may initiate type 2 immune responses. However, the allergen-induced signals orchestrating the release of IL-33 and Th2 immunity remain poorly defined. We here identified the G-protein coupled receptor, formyl-peptide receptor 2 (FPR2) and its endogenous ligand, the acute phase protein serum amyloid A1 (SAA1) as major drivers of the allergic response, through their ability to enhance IL-33 release from airway epithelial cells and regulate cytokine secretion from lymphocytes of both the innate and adaptive immune system. This process was dependent on the binding of SAA1 to cytosolic fatty acid binding proteins present in allergenic extracts that could act as a mimic of an endogenous danger signal. More importantly, our data indicated that allelic variants of SAA1 differ in their IL-33 inducing capacity, which might have a previously unrecognized implication for human type 2 pathologies. Overall, we propose a new paradigm for the role of SAA1 in the initiation of type 2 immunity via the localized and thus restricted unmasking of the proinflammatory effects of SAA1 at mucosal surfaces. Allergic asthma is one of the major worldwide environmental health problems highlighting the need for the development of disease modifying therapies. Understanding how the airway epithelium senses and is activated by allergen encounter to alert both innate and adaptive immune cells is essential for understanding the mechanism of susceptibility to allergic asthma. The data obtained in this project should inform the development of safe and effective strategies for the treatment of this debilitating disease.