There are two types of walnut, those most commonly found across Europe and Asia are known as English Walnut and those found in Canada and the US are called Black Walnut, they are distinct species with different allergenic proteins.

Black walnuts, Juglans nigra, have 3 key allergens, Jug n 1 is a 2S albumin protein. Jug n 2 is a vicilin like protein, these are often also referred to as 7S seed storage proteins.. Jug n 4 is a legumin protein, also known as 11S seed storage proteins.

English walnuts, Juglans regia, have 8 identified allergens, which in addition to the 3 seed storage proteins above also have a Bet v 1 like protein (also known as PR-10), profilin proteins and 2 lipid transfer proteins (LTP).

You may have Pollen-Food Allergy Syndrome if you suffer from oral allergy symptoms to 3 or more of the foods mentioned in cross reactivity section.

There is also a link between walnuts and Latex Food Syndrome. The plant involved in latex allergy Hevea brasiliensis, the rubber tree plant, has an allergen called Hev b 8 which is a profilin protein. Those very sensitised to latex may have a contact allergic reaction from other foods or plants containing profilin proteins, there is less evidence of this than sensitisation to other latex linked proteins like hevein and chitinases.

Allergy to walnuts is sometimes linked to Celery-Mugwort-Spice Syndrome as the sensitising allergen is a profilin protein called Art v 4, these proteins are also sometimes also called Bet v 2 proteins.

English walnut allergy is often linked to LTP Syndrome, where similarly shaped proteins in other plants resemble those in walnuts and elicit an allergic reaction.

Other food containing 2S albumin seed storage proteins are cashews, peanuts, almonds, mustard seed, rapeseed, turnip, chickpeas, brazil nuts, pistachio, buckwheat, soya beans, sunflower seeds, hazelnuts, kiwi, castor beans and sesame seeds.

There is a lot of cross reactivity between 2S and 11S seed storage proteins, the only other food containing 11S proteins not mentioned above is pumpkin.

Other foods containing 7S seed storage proteins not mentioned in the list above are lupin, lentils, macadamia, peas and mung bean.

If sensitised to birch tree pollen you may also react to apple, kiwi, pear, peach, plum, nectarine, apricots, cherries, tomato, celery, carrot, potato, parsnip, pepper, dill, cumin, peas, coriander, fennel, hazelnut, almonds, peanuts, lentils and beans.

Other foods containing profilin allergens are celery, peanut, soyabeans, lychee, lupin, almonds, mustard, hazelnut, kiwi, pineapple, chilli, melon, orange, strawberry, apple, banana, aubergine (eggplant), peach, pear, tomato, dates, cherry, carrot, barley and wheat. Allergic reactions to some of these foods may be considered a marker of profilin hypersensitivity.

Common foods involved in LTP allergy include kiwi, strawberries, sunflower seeds, walnut, apple, mulberry, banana, pea, apricot, cherry, plum, almond, peach pomegranate, raspberry, tomato, grape, celery, peanut, asparagus, cabbage, broccoli, chestnut, lemon, tangerine, orange, hazelnut, lettuce, lentils, lupin, green bean, pear, mustard, wheat and maize.

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