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Allergies are a complex of symptoms derived from altered IgE-mediated reactions of the immune system towards substances known as allergens. Apple and hazelnut allergens have been identified in pollens or fruits. Apple allergies are due to four different classes of allergens (Mal d 1, 2, 3, 4), whose allergenicity is related both to genotype and tissue specificity. Building by Homology technique was applied to predict the 3D structures of Mal d 1-4. Starting from the comparison of these results leading to understand the different ways of reactions of the Malds, we have studied the answer of sensitised individuals to 11 apple genotypes, separating fruits skin positive answers from those to the pulp through Skin Prick Test and prick-to-prick test, evidencing different allergic responses to the different cultivar. Climate changes resulting from increases in temperature and air pollution influence pollen allergenicity, responsible for the dramatic raise in respiratory allergies (hay fever, bronchial asthma, conjunctivitis). Although the link between climate change and pollen allergenicity is proven, the underlying mechanism is little understood. Transglutaminases (TGases), a class of enzymes able to post-translationally modify proteins, are activated under stress and involved in some inflammatory responses, enhancing the activity of pro-inflammatory phospholipase A2, suggesting a role in allergies. Aero allergenic (hazelnut. Corylus avellana) and enthomophylus (apple. Malus domestica) pollen exposed to climate changes (different temperatures, relative humidity (rH), acid rain at pH 5.6 and copper pollution (3.10 µg/l)) showed an increase in pollen surface TGase activity in Corylus, while Malus pollen TGase was not significantly affected. Several pollen proteins were post-translationally modified, including the activation of mammalian sPLA2, thus potentially altering pollen allergenicity and inflammation. Western blotting of pollen TGase revealed its induced expression after exposure to stressors, while detection of in situ TGase activity and morphological examination indicated pollen damage and release of TGase. Grants:Crossallergenicity Progetto Strategico d’Ateneo E.F. 2006,University of Bologna