Allergen Exposure
Geographical distribution
Sweet Chestnut is a shade-tolerant deciduous tree native to southeastern Europe, Asia Minor, and North Africa. Several edible species of Chestnut are grown around world, the 4 main species being Sweet chestnut (C. sativa), Chinese chestnut (C. mollissima), Japanese chestnut (C. crenata), and American chestnut (C. dentata). American chestnut has been decimated by parasites. China, Korea and Italy are the world's largest producers of Chestnuts. The principal European producers are Italy, Spain, Portugal, France, and Greece.
The tree can attain a height of 35 m and a trunk diameter of 2 m. The bark is deeply grooved or fissured in a net-shaped (retiform) pattern, sometimes in a spiral. The flowers of both sexes are borne in 10-20 cm-long, upright catkins, the male flowers in the upper part of the tree and the female flowers in the lower part. By autumn the female flowers, in bunches of 2 or 3 (and up to 7), develop into light-green fruit cupules (husks) covered with sharp spines; each cupule usually contains 2 dark, shiny, red-brown nuts and, with the nuts ripened, is shed during October. Trees start to bear nuts when 30-40 years old.
Raw nuts have a bitter taste from tannins, which improves considerably with cooking, developing into a sweet and nutty flavour, with a texture like a firm baked potato - unlike other nuts, which are crunchy. Chestnuts, unlike other nuts, contain very little fat or oil (2-3%), compared to over 50%; they consist mainly of complex carbohydrate (50%) and water (40-45%), with small amounts of protein (5-10%). They contain no cholesterol. They have been part of the staple diet and a major source of complex carbohydrate in Southern Europe, Turkey and Asia for centuries.
Environment
Edible Chestnuts have been grown for culinary purposes for centuries and can be consumed fresh, boiled, grilled, or roasted. They can be frozen or pureed for desserts or confectionery, or used in stuffing or as a garnish. Dried Chestnuts should be soaked in water, cooked, and then treated as fresh.
Traditionally, Chestnuts are roasted over an open fire or in the oven. They can be dried, ground and used as flour in breads and puddings, or as a thickener in soups. The roasted nut can be a coffee substitute. Some notable specialties include porridge (Italy) and Chestnuts preserved in sugar (marron glacé, a French delicacy). The Corsican variety of polenta is made with Sweet chestnut flour. A variety of Corsican beer has Chestnut as one of its ingredients.
Allergens
Chestnut is the third most-prevalent food allergen among both adult and pediatric allergy patients in Korea. At least 21 IgE-binding components have been isolated, and 9 protein bands appear to be major allergens. A heat- and digestion-labile 24 kDa protein with homology to a legume protein of Oak acorn was reported to have the highest binding intensity (1). The 24 kDa component bound to more than 50% of asymptomatic Chestnut-sensitised subjects, with minimal binding in symptomatic Chestnut-sensitised subjects; and a component of 29 kDa bound to more than 50% of symptomatic Chestnut-sensitised subjects, with minimal binding in asymptomatic Chestnut-sensitised subjects. A later study further evaluated these 2 components, the 24 and 29 kDa allergens. Simulated gastric digestion decreased IgE binding of the most significant allergens, except the 24 kDa one, while minimal changes were noted to occur through SIF (intestinal enzymes). Boiling treatment could decrease IgE binding components of the most significant allergens, including the 24kDa one (2).
To date, the following allergens have been characterised:
- Cas s 5, a chitinase, an approximately 32 kDa protein, a major allergen (3-9).
- rCas s 5 (3).
- Cas s 8, a Lipid Transfer Protein, a 9.7 kDa protein, a major allergen (10-12).
Cas s 5 belongs to the Class I chitinases, enzymes that contain an N-terminal hevein-like domain homologous to Latex hevein (Hev b 6.02), and a larger catalytic domain. They are the major panallergens in fruits associated with Latex-fruit syndrome (3,5,9). Recombinant Cas s 5 is homologous to its natural counterpart (3).
Although Chestnut allergy is strongly associated with Latex-fruit syndrome, Chesnut allergy may occur independently of this syndrome and has been attributed to the presence of Cas s 8, a Lipid Transfer Protein. In a study of 12 patients sensitised to Chestnut but not to Latex, along with 3 control patients with Latex-Chestnut allergy, a Lipid Transfer Protein was isolated and found to bind to serum-specific IgE in 91% (as shown by IgE immunoblotting) and 58% (as shown by ELISA) of sera from patients with Chestnut but not Latex allergy. Sixty-six percent of these patients had positive skin prick test responses to Cas s 8. Allergenic LTPs from Peach fruit and Artemisia vulgaris pollen were also reactive. In contrast, Avocado class I chitinase and Latex hevein, allergens associated with Latex-fruit syndrome, showed no reaction. The authors suggested that LTPs and class I chitinases can be used as diagnostic tools in patients with Chestnut allergy, to predict whether an associated Latex sensitisation and a risk of cross-reactivity with other plant foods and pollens exist (7).
Cas s 1 and 2 other allergens, an IPR-protein and a profilin, have been isolated from the pollen of European chestnut tree but have not to date been shown to be present in Sweet chestnut (13).
Potential cross-reactivity
Approximately 30-50% of individuals who are allergic to Natural rubber latex (NRL) show an associated hypersensitivity to a number of plant-derived foods, especially freshly consumed fruits (14-17). Some authors have called this the Latex-fruit syndrome, and foods associated include Avocado, Banana, Sweet Chestnut, Kiwi, Peach, Tomato, Potato and Bell pepper (in approximate decreasing order of relevance). Fig, Pineapple and Peanut have also been implicated (18-21). A number of plant protein families have been shown to be involved in Latex-fruit syndrome. Two of these are also pathogenesis-related (PR) proteins. Class I chitinases have been identified as a major category of IgE-binding allergens for patients allergic to NRL. A beta-1,3-glucanase was identified as an important Latex allergen that shows cross-reactivity with proteins of Bell pepper. Another important NRL allergen, Hev b 7, is a patatin-like protein that shows cross-reactivity with its analogous protein in Potato (19). Furthermore, patients with allergy to plant-derived foods and associated pollen allergy show a high frequency of IgE reactivity to the panallergen profilin. However, whether Latex sensitisation precedes or follows the onset of food allergy has not been resolved (16).
Allergy to Chestnuts has been widely reported in connection to Latex-fruit syndrome. However, few studies address actual allergy to Chestnuts in patients reacting primarily to this food. In this study, 22 consecutive subjects with proven allergy to Chestnut (according to DBPCFC or a convincing history of anaphylaxis) were studied. The age of onset of reactions to Chestnut ranged from 5 to 70 years, with 8/22 (36%) patients having experienced severe anaphylactic episodes. SPTs with Chestnut were positive in 71%, and IgE antibodies were detected in 54% of patients. Eighty-six percent and 59% of patients also had positive responses to pollen and Latex allergens, respectively. Eighteen patients had actual allergy to other foods, of which these were the main ones: Banana, in 45% of patients; Avocado, in 40%; and Hazel nut, in 32%. There was a significant association between sensitisation to Latex and clinical reactivity to Avocado and/or Kiwi (p<0.01); while reactivity to Hazel nut was associated with allergy to Peanut (p=0.003) and Walnut (p<0.001) (22).
In a study of 47 Latex-allergic patients, immunological reactivity to foods was found in 33. Seventeen patients manifested a clinical allergy to at least 1 food, including 11 patients with anaphylaxis and 14 with local sensitivity reactions. Positive food skin tests occurred most frequently with Avocado (53%), Potato (40%), Banana (38%), Tomato (28%), Chestnut (28%), and Kiwi (17%) (19).
Chestnut and Natural rubber latex (NRL) allergy are often associated in Latex-fruit syndrome. This study's aim was to establish whether concurrent NRL and Chestnut IgE antibody reactivity are the results of co-sensitisation or cross-reactivity.
Sera from 19 patients with Chestnut- and NRL-specific IgE were selected and tested for reactivity with recombinant (r) Latex allergens. IgE-antibodies were detected to rHev b 6.01 (prohevein) in 58% of the sera, to rHev b 5 in 32%, to rHev b 12 in 4 of 13 sera, to rHev b 7.02 and rHev b 11 in 4, and to rHev b 1 in 2 of 19 sera. rHev b 8-IgE antibodies were found in 9 sera (47%), whereas 6 displayed monosensitisation to rHev b 8 with regard to the test panel. Three of 16 sera showed IgE to cross-reactive carbohydrate determinants. In most sera recognising rHev b 5 and/or rHev b 6.01 as major allergens, the IgE reactivity to NRL remained unaffected by Chestnut extract, and Chestnut IgE remained unaffected by NRL extract. Conversely, in sera with rHev b 8 as the dominant allergen, IgE-binding to NRL was nearly completely inhibited by Chestnut and vice versa. IgE-binding to rHev b 8 was abolished by Chestnut extract. The study concludes that although patients have concomitant IgE antibody reactivity to Chestnut and NRL, cross-reactivity could be demonstrated mainly in those patients with IgE to Hev b 8 (profilin) from NRL (23).
However, the prevalence of combined NRL and Chestnut allergy may vary according to the population in question and may be very low in some groups. Among 137 patients with NRL allergy, food allergy to Chestnut was reported in only 1 patient. (24) In a Taiwanese screening program to identify Latex-sensitised hospital employees, elevated serum total IgE was found in 22(16.9%) of 130 nurses, 3(16.7%) of whom had increased Latex-specific IgE, further confirmed by SPT determination. No cross-reactive fruit allergy (Melon, Banana, Kiwi, Tomato, or Chestnut) was found among the Latex-sensitised nurses (25).
Of the plant protein families, a Class I chitinase containing an N-terminal hevein-like domain homologous to and cross-reacting with hevein (Hev b 6.02) has been shown to be a major panallergen responsible for Latex-fruit syndrome involving cross-reactivity among Chestnut, Banana and Avocado (5-6,9,14-15,26-28). Class I chitinases have also been detected in Cherimoya, Passion fruit, Kiwi, Papaya, Mango, Tomato, and Wheat flour extracts (29). Cross-reactivity is modulated due to chitinase in the Latex plant (Hev b 11), which displays 70% identity to the endochitinase from Avocado and its hevein domain, and 58% to hevein in Latex (Hev b 6.02). Hev b 11, a class I chitinase, displays a different IgE binding capacity than hevein (4).
A review of 28 cases of sensitisation to Latex showed that Banana- and Chestnut-induced allergies were the allergies most frequently associated with Latex-induced allergy (30). In a study of 25 patients with Latex allergy (9 [36%] with anaphylaxis), 13 (52%) were found to have concomitant food allergies to a total of 42 foods, of which 23 had caused systemic anaphylaxis. The most frequent food hypersensitivities were to Avocado (n=9), Chestnut (n=9), Banana (n=7), Kiwi (n=5) and Papaya (n=3). Cross-reactivity among Latex, Avocado, Chestnut, and Banana was demonstrated (31).
A report was made of 8 patients allergic to Latex and Fruit (Chestnut and Banana), 4 of whom had experienced anaphylaxis following ingestion of the fruit. In the 6 patients with symptoms after eating Chestnuts, SPT for Chestnut was found in 5. Histamine release to Chestnuts was positive in 3 of the 6. One patient with no skin reactivity to Chestnut, but showing IgE antibodies in serum tests, tolerated the fruit. Other case reports are illustrative of Chestnut allergy. Patient 1, a 32-year-old housewife, experienced itching of the mouth, rhinitis, and facial angioedema 30 minutes after eating a raw Chestnut. Patient 2, a 23-year-old sister of Patient 1, developed itching of the palate, sneezing, nasal discharge and asthma 10 minutes after eating Chestnuts. Patient 4, a 20-year-old housewife, 10 minutes after ingestion of Bananas and Chestnuts, developed asthma, rhinitis and urticaria. Patient 6, a 23-year-old woman student, experienced anaphylactic episodes (general urticaria, angioedema, and asthma) following the ingestion of Chestnuts and Bananas. Patient 7, a 42-year-old housewife, had an anaphylactic reaction after eating Chestnuts. Patient 8, a 17-year-old female student, developed generalised urticaria and angioedema with laryngeal involvement after eating Chestnuts, and ingestion of Banana caused itching of the mouth (32).
Similarly, a report describes an 8-year-old boy, with a number of previous surgical procedures, who developed acute episodes of urticaria following contact with NRL, and then angioedema and dry cough after ingestion of Chesnuts. SPT for Latex and Chestnut was positive. IgE antibodies were detected to Latex but not to Chestnut. Open oral challenge with Chestnut was positive: 15 minutes after ingestion of 0.5 g of Chestnut, he developed bouts of sneezing, dry cough, perioral itching and erythema, and isolated facial wheals (20).
However, not all studies indicate that sensitisation to Chestnut, or cross-reactivity between Latex and Chestnut, is clinically relevant. For example, in a Turkish study investigating the prevalence of Latex and Latex-associated food sensitivities among hospital employees and atopic children – 61 hospital employees and 40 atopic children – allergen-specific IgE evaluation confirmed sensitisation to NRL in 30 subjects, but not all were symptomatic. Chestnut sensitisation was demonstrated in 37, but whether these individuals displayed allergic symptoms for Chestnut was not investigated; yet the implication that sensitisation may occur without allergic expression is apparent (33). Other authors concur, suggesting that serologic tests seem to be of low significance for prediction of food allergy in Latex-allergic patients, and that in many cases, sensitisation occurs with no clinical expression (15,34).
Cross-reactivity has also been described between Avocado and Chestnut. In a study of 17 patients with immediate hyper-sensitivity to Avocado, common antigenic determinants were shown to exist among Avocado, Latex, Chestnut, and Banana extracts (35). Recent knowledge suggests that the panallergen chitinase may have been responsible.
Although Chestnut allergy is strongly associated with Latex-fruit syndrome, Chesnut allergy may occur independently of this syndrome and has been attributed to the presence of Cas s 8, a Lipid Transfer Protein (7). Cross-reactivity with other foods containing LTPs is therefore possible. In a study evaluating, by means of SPT, the reactivity to LTPs from Peach, Apple, Chestnut and Artemisia pollen, Chestnut LTP was reported to be less cross-reactive than Apple and Peach LTPs. In a group of Peach-allergic individuals, the most frequent pattern of cross-reactivity of LTPs was the combination Peach-Apple (45%), followed by Peach-Apple-Artemisia-Chestnut (21%). Significant correlations were found between Peach and Apple LTPs, and between Artemisia and Chestnut LTPs. Positive SPTs to Chestnut LTP were observed only in patients with positive SPTs to Artemisia LTP. All the patients with positive case histories to Chestnut reacted to Chestnut LTP. (11) This is in particular relevant in Rosaceae fruit-allergic populations in the Mediterranean area, where LTPs have been identified as major allergens, especially in Apple and Peach. Purified LTPs from Artemisia pollen and from Chestnut meat have a 43-50% sequence identity with the equivalent allergens of Apple and Peach. A similar degree of sequence identity (50%) was found between the Artemisia and Chestnut proteins. Therefore, although LTPs from Artemisia pollen and Chestnut cross-react with LTPs of Rosaceae fruits, significant differences in specific IgE-binding capacities have been noted among members of the plant LTP family (10).
The study also demonstrated that Latex-allergic patients (23%) recognise a protein with sequence homology to the protein family patatin, known to be an important protein in Potato. Cross-reactivity between Latex and several Potato proteins was observed through immunoblot inhibition analysis (19).
In 4 patients with an allergy to Ficus benjamina, 2 patients had a cross-allergy to NRL and the associated cluster of tropical fruit (Banana, Kiwi, Avocado, and Chestnut) (36).
The enzymes Papain and Bromelain may share epitopes with Chestnut allergens (14,26).
According to a report of a 4-year-old boy who developed allergic symptoms immediately after peeling and eating an Oak acorn, partial cross-reactivity was demonstrated between Oak acorn and Chestnut (37).
Clinical Experience
IgE-mediated reactions
Allergy to Chestnut on its own is infrequent, considering how common Chestnut consumption is in certain countries (38); but Chestnut allergy is more frequently associated with the complex sensitisation of NRL-allergic individuals to fruits and vegetables (14-17,24). However, it may be that allergy to Chestnut is underreported, since the possibility of allergic disease tends to be insufficiently investigated. In a Korean study evaluating the clinical significance of Chestnut as a food allergen in 1,738 patients with respiratory allergies, skin reactivity to Chestnut was found in 56 (3.2%) (1).
A study investigating the prevalence of NRL sensitisation and allergy in 74 children with atopic dermatitis reported that 12 of the 74 atopic children had IgE antibodies to Latex. Twenty children without proven Latex sensitisation showed increased food-specific IgE, most frequently to Potato, Banana, and Chestnut (39).
Oral allergy syndrome induced by Chestnut, followed by rhinoconjunctivitis and asthma, has been described in a 22-year-old woman. She reported that when chewing Chestnut, she had felt a burning sensation and itching of the oropharyngeal mucosa followed by lacrimation, nasal pruritus, violent sneezing salvos, and “moderate” difficulty in breathing, but not severe enough to require treatment. Symptoms initially had been relatively minor and limited to oral ones, but subsequent episodes became progressively worse. The challenge with fresh food was positive. Skin prick test with a commercial product and the prick-by-prick method with fresh Chestnut were negative. Skin prick testing with a freshly prepared extract of fresh Chestnut, and the passive transfer reaction, were positive. Serum tests were negative (40).
Four cases of nurses with allergy to NRL followed by anaphylaxis to Chestnut were reported. The presence of Chestnut sensitivity was demonstrated by positive SPT, but IgE antibodies to Chestnut were found in only 2, suggesting that anaphylaxis to Chestnut is possible even in the absence of serum IgE antibodies to Chestnut (41). Anaphylaxis to Chestnut may be classified as “idiopathic” until investigated further (42).
A 4-year-old boy developed ocular itching, eyelid and lip angioedema, unproductive cough, wheezing and dyspnoea immediately after peeling and eating an Oak acorn. Months later, he experienced similar symptoms after eating a Chestnut. He tolerated Latex and Banana. SPT was positive to Oak acorn peel and Chestnut, and negative to the pollen. The IgE antibody level was raised for Chestnut and Oak acorn peel, with a degree of cross-reactivity demonstrated between these foods (37).
Chestnut has been reported to cause urticaria-angioedema in a 29-year-old man (43).
Other reactions
Chestnut tree pollen is an aeroallergen (44).
The Horse chestnut, Aesculus hippo-castanum, is an entirely different tree from the Sweet chestnut. The Horse chestnut is not edible; its burs have blunt spikes, while Sweet chestnut burs are very sharp and spiny.
Compiled by Dr Harris Steinman, harris@zingsolutions.com