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 have 3 key allergens, Jug n 1 (2S albumin protein), Jug n 2 (vicilin like protein) and Jug n 4 (legumin protein).
English walnuts have 8 identified allergens, which in addition to the proteins above also has PR-10 (proteins involved in oral allergy syndrome), 11S storage proteins, profilin proteins and 2 lipid transfer proteins (LTP).
English walnut allergy is often linked to LTP Syndrome, where similarly shaped proteins in other plants resemble those in almonds and elicit an allergic reaction.
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.
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.
If sensitised to Birch 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 food containing 2S albumin seed storage proteins are cashews, peanuts, almonds, mustard seed, rapeseed, turnip, chickpeas, hazelnuts, pistachio, buckwheat, soya beans, sunflower seeds, brazil nuts, 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 vicilin like proteins not mentioned in the list above are lupin, lentils, macadamia nuts, peas and mung bean.