Published Online: March 14, 2015
Hazelnut allergy is the most common food allergy in Europe. This is one of the outcomes of a large multicenter study called EuroPrevall, carried out in twelve European cities, including Reykjavik, Athens, Vilnius, and Madrid. Until now, reliable information about hazelnut allergy in Eastern Europe, the Eastern Mediterranean, and the Northwestern Atlantic has been unavailable. However, with their recent publication in The Journal of Allergy and Clinical Immunology (JACI), Datema and colleagues fill this gap, characterizing hazelnut allergic patients across Europe.
It has long been known that hazelnut allergy in Central and North-Western Europe is mostly observed in patients allergic to tree pollen, in particular to birch pollen. This “marriage” is explained by a phenomenon called cross-reactivity of IgE antibodies, the antibodies responsible for allergic disease. IgE antibodies causing tree pollen allergy also react with hazelnut because tree pollen and hazelnut contain related allergens. This very common cross-reactive hazelnut allergy is in fact always quite mild.
More severe hazelnut allergies are much rarer and are independent from tree pollen allergy. There are multiple types of hazelnut allergy with potentially more severe outcomes, each caused by different allergenic components or molecules of hazelnuts. One type is caused by the abundant seed storage proteins of the nut, the other by a molecule called lipid transfer protein (LTP), present in the nuts in much lower quantities. In contrast to the more common tree pollen-related hazelnut allergy, these potentially more severe allergies most likely develop in response to consumption of hazelnut (in case of the seed storage proteins) or of other foods (in case of LTP). The food most commonly implicated in food allergies caused by LTP is peach. Interestingly, LTP-related food allergies have mainly been observed in Spain and Italy.
Datema and colleagues show that birch pollen allergy is the driving force behind most hazelnut allergy, as observed in Western and Central Europe. In serum of most patients from these cities, IgE antibodies are found reacting with the tree-pollen related molecules. In cities where exposure to birch pollen is very low, such as Reykjavik, Athens, and Madrid, hazelnut allergy appears to be much rarer. In particular, in Athens but also in Madrid, LTP is the leading allergen. Interestingly, in Athens this is not only associated with peach allergy but also with walnut allergy. Finally, hazelnut allergy linked to storage proteins is rare, but found across Europe, mainly in children.
Datema and colleagues are now investigating how these different patterns of recognition of hazelnut allergens across Europe are linked to different clinical presentations, in particular to severity of the disease. The outcome of these studies will improve diagnostic tests for hazelnut allergy.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.