Frequent episodes of adult soybean allergy during and following the pollen season

Abstract

The pollen-food syndrome (PFS) is one of the most common forms of food allergy in adults and adolescents. Allergic reactions to foods are explained by primary respiratory sensitization to pollen and IgE cross-reactivity between the pollen allergen and its homologous allergens in foods. In clinical practice, increased food-triggered allergic symptoms during or after the pollen season are observed in some patients with PFS, thought to be due to seasonal boosting of pollen-IgE levels. We consider that whether there is indeed a seasonal variation in food allergic symptoms is an important issue for the long-term management of patients with PFS. However, clinical evidence that supports seasonal variation has been quite limited so far, although there is one study that reports an increased clinical reactivity to apples during the birch pollen season. The aim of the present study was to clarify seasonal variation in severe allergic episodes of pollen-related food allergy. Here, we focused on the association between Betulaceae and Fagaceae pollen counts and increased episodes of severe allergic symptoms after soybean ingestion. We performed a retrospective medical chart-based review on consecutive adult patients with soybean allergy who first visited the food allergy department of Sagamihara National Hospital between October 2008 and September 2013. Soybean allergy was defined as meeting two criteria: (1) positive case history of immediate allergic symptoms after ingestion of soy products and (2) positive skin prick test results to soybean extract (extract “edamame,” Torii, Tokyo, Japan) and/or the causative soy product. First, we screened 85 consecutive patients with soybean allergy after reviewing charts of all outpatients during the study period, and gathered detailed information on symptoms that occurred after soy intake, including the day, month, and year when they had symptoms. Although the most common symptoms of soy allergy are restricted to the oral cavity, the subjects studied here were limited to those who had experienced systemic allergic symptoms (n 1⁄4 26) after soybean ingestion. Of these, 4 were excluded because data on the day, month, and year when they had symptoms were missing. Thus, 22 patients were finally included. The Ethics Committee of Sagamihara National Hospital approved the study protocol. Levels of serum IgE antibodies specific for alder pollen, soybean extract, recombinant Bet v 1 (rBet v 1), rGly m 4, native Gly m 5 (nGly m 5), and nGly m 6 were determined using a commercially available ImmunoCAP system (Thermo Fisher Scientific, Uppsala, Sweden). A level of IgE antibody 0.35 kUA/L was regarded as positive according to the manufacturers recommendation. Counts of airborne Betulaceae and Fagaceae pollen were recorded using a Durham gravity sampler on the roof of the Sagamihara National Hospital during the study period. Demographic and clinical characteristics of the 22 patients studied are shown in Table I. Twenty-one (96%) of them reported nasal allergic symptoms during the Betulaceae and Fagaceae pollen season (data not shown). They experienced a total of 33 episodes of systemic allergic symptoms after soy intake. We identified the timing of these episodes from the medical records. The most frequent offending soy product was soymilk (n 1⁄4 21), followed by tofu (n 1⁄4 3), and bean sprouts (n 1⁄4 3), consistent with previous studies. Details of the 22 patients are shown in Table E1 of this article’s Online Repository at www.jaci-inpractice.org. All patients were found to be sensitized to alder, the birch pollen major allergen, Bet v 1, and its homologous allergen in soy, rGly m 4. This indicates that all the patients can be regarded as having pollen-related soybean allergy.