Environment-related cross reactions are very closely related to allergies since they always involve the activity of our immune system. At its most basic level, cross reactivity involves the ability of our immune system to recognize similarities between all types of allergens regardless of their source. Earlier in this article, we focused specifically on food allergens that our immune system gets exposed to through the process of eating. But things we do not eat can also contain allergens, and if these allergens closely resemble certain protein structures in our food, cross reactions can occur. When cross reactions occur, our immune system ends up responding to a second protein structure in the same way that it responded to the initial allergen. For example, we might breathe in pollen from a birch tree during the season in which birch trees release their pollen. (The specific season depends on geography and climate, but in most cases, birch tree pollen is most abundantly present in late winter and early spring.) Inside of birch pollen is a potential allergen called Bet v 1. Our immune system can react to this birch pollen allergen, and as a result, we can end up with a seasonal allergy to this tree pollen.
Now let's consider the food side of this cross reaction. Inside the protein structure of an apple, there is a protein molecule called Mal d 1. This molecule is similar to the Bet v 1 molecule found in birch pollen, and it can also act as an allergen. Because our immune system can recognize the similarity between the Mal d 1 molecule in apples and the Bet v 1 molecule in birch pollen, we can end up not only with a seasonal tree pollen allergy, but with a year-round allergy to apples as well. This phenomenon is referred to as a cross reaction, and in this case, it involves a cross reaction between an inhaled molecule in the environment (birch tree pollen), and a molecule in food (apple allergen).
While there are a virtually limitless number of possible allergenic cross reactions, five categories seem especially important when considering environment-related allergens and food. The five basic categories involve: (1) alder tree pollen, (2) grass pollen, (3) mugwort weed pollen, (4) ragweed pollen, and (5) birch tree pollen. A particularly large number of foods appear to be involved in cross reaction with birch tree pollen.
Below is a chart listing these five categories of cross reaction and some of the key foods involved. This chart is not intended to represent all possible environmental allergens, or all possible cross-reacting foods. Instead, it is meant to provide you with examples of common pollen allergens and commonly cross-reacting foods.
|Environmental Allergen||Cross-Reacting Foods|
|alder tree pollen||almonds, apples, celery, cherries, hazelnuts, peaches, pears, parsley|
|grass pollen||melons, tomatoes, oranges|
|mugwort weed pollen||carrots, celery, coriander, fennel, parsley, bell peppers, hot peppers, sunflower seeds|
|ragweed pollen||bananas, cantaloupe, cucumbers, zucchini, honeydew, watermelon, chamomile|
|birch tree pollen||almonds, apples, apricots, carrots, celery, cherries, coriander/cilantro, fennel, hazelnuts, kiwifruit, lychee fruit, nectarines, oranges, parsley, parsnips, peaches, pears, bell peppers, hot peppers, persimmons, plums/prunes, potaotes, soybeans, wheat|
While widely publicized and extensively researched, latex-fruit syndrome is well-documented food sensitivity that has been shown to occur worldwide but has yet to be fully understood. Researchers are not sure about the exact nature of latex-fruit syndrome, even though they know it is a real phenomenon experienced by many people.
The environmental allergens in latex-fruit syndrome come from the rubber tree (Hevea brasiliensis). When latex is produced from natural sources (versus synthetically manufactured), this rubber tree is the most widely used source for obtaining the thick sap that can be processed into latex. Early studies on latex-fruit syndrome focused on hevein-related proteins in natural rubber latex, including Hev b 1, Hev b 2, Hev b3 (and so forth) all the way up to Hev b 12. However, scientists now know that these hevein-related allergens are not the only allergens found in latex. (For example, other allergens include heat shock proteins, proteasome subunits, protease inhibitors, and hevamines.)
In addition to this diversity of allergens contained in natural rubber latex, there is an equal diversity of similarly shaped protein molecules in numerous foods. On this food side of the equation, researchers originally focused on food proteins belonging to the enzyme family called class I chitinases, including Pers a 1 from avocado and Cas s 5 from chestnut. At present, however, scientists know that more types of food proteins may be involved in latex-fruit syndrome, outside of this class I chitinase family.
The best-researched foods known to be involved in latex-fruit syndrome are banana, avocado, and chestnut. Although the research on kiwifruit is somewhat controversial, many observers would put kiwifruit in this same uppermost list. After the foods listed above, foods most commonly associated with latex-fruit syndrome include papaya, potato, tomato, apple, carrot, and melons. However, even within this relatively short list of foods, there is considerable controversy and lack of consensus. In bananas, for example, food scientists have identified at least 16 different allergens, with only 2 belonging to the class I chitinase family possessing hevein-like proteins. Researchers do not know for certain what role these different banana allergens might or might not play in latex-food syndrome.
Over two dozen additional foods have been proposed as being involved in latex-fruit syndrome, and these foods include: apricot, cherries, mango, peach, grapes, figs, citrus fruits, lychee, nectarines, passion fruit, pears, persimmons, pineapple, strawberries, almonds, hazelnuts, walnuts, pistachios, sunflower seeds, peanuts, peas, beans, lentils, soybeans, chickpeas, eggplant, capers, lettuce, zucchini, shellfish, wheat, buckwheat, rye, bell and hot peppers, dill, oregano, sage, and coconut. As you can see, this list is a long and confusing one, and unlikely to be helpful in helping you identify possible food sensitivities. The shorter list of foods above (as noted in the previous paragraph), however, might be helpful for you to consider as possible mismatched foods in your meal plan if you have already identified latex allergy as a personal health issue. In this particular area of cross reaction between environmental allergens and food allergens, the jury is still partially out. But there is still a solid core list of about 10 foods—banana, avocado, cherries, kiwifruit, papaya, potato, tomato, apple, carrot, and melons—that deserve to be considered as potentially problematic in the wake of latex allergy.
Environment-food cross reactions can be as complicated or even more complicated to recognize as food allergies and food intolerances. On the environment side, they might be seasonal and only a problem during certain times of year. On the food side, they are likely to be year round, and may involve a half dozen or more foods. Due to all of these complicating factors, cross reactions may often require the help of a healthcare provider to correctly identify.