Birch pollen allergy may forewarn of allergy to apples and hazelnuts in some, but not in others –exploring the mystery
Birch pollen-allergic patients commonly have seasonal hayfever and allergic asthma. Many also develop allergies to certain plant foods such as apple, cherry, pear, carrot, peanut, celery, soybean, and hazelnut. This “birch-fruit-vegetable” or oral allergy syndrome (OAS) can manifest as itching, and sometimes swelling, of the lips, tongue, and throat and occasionally, more severe reactions such as skin rash and hives, asthma, and anaphylaxis may occur. The food allergy is thought to result from a cross-reaction between birch pollen allergens and food proteins with similar structures. Interestingly, however, birch pollen-allergic patient who have IgE antibodies to food allergens related to birch pollen often do not have symptoms when consuming those foods. Recent studies have suggested that IgG antibodies might figure into this mysterious food tolerance.
In an article published in the Janaury 2011 issue of The Journal of Allergy and Clinical Immunology (JACI), Geroldinger-Simic et al evaluate the prevalence, main symptoms, and triggers of birch pollen-related food allergy and investigate the role of allergen-specific IgG4 antibodies in patients tolerant to birch pollen-related foods. Studying a group of 225 birch pollen-allergic individuals, they evaluated food-induced symptoms and measured IgE and IgG4 levels for the major birch pollen allergens and apple and hazelnut allergens. Seventy-three percent of the study group experienced food allergy symptoms and 86% of those affected with the food allergies experienced symptoms year-round, not just during the pollen season.
The authors conclude that birch pollen-related food allergy is a highly prevalent, perennial disorder and found that apple and hazelnut were the most common triggers of the food allergy. Comparing the IgG4 levels of patients who reacted to foods and those who did not, the authors found that the ratio of IgG4 to IgE was significantly higher in food-tolerant patients than in food-allergic patients. This, the authors suggest, is a result of specific IgG4 blocking the IgE that binds to food allergens and causes an allergic reaction.
Further studies into the mechanisms associated with birch pollen-related food allergy could lead to new treatment strategies for this disease.
The Journal of Allergy and Clinical Immunology (JACI) is the official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.