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Background: When skin prick testing (SPT) young children with atopic dermatitis (AD) for suspected food allergy, we frequently found positive reactions with turnip rape (Brassica rapa) and oilseed rape (Brassica napus). We performed food challenge to examine whether these children react clinically to turnip rape.
Methods: A total of 1887 children were screened with SPTs for sensitization to turnip rape and oilseed rape. Twenty-eight children with clearly positive SPT (≥5 mm) were first subjected to labial challenge with turnip rape seeds followed, if negative, by open oral challenge for up to 7 days. Twenty-five children with AD but negative SPT to turnip rape and oilseed rape served as controls.
Results: Two-hundred and six (10.9%) children had positive SPT to turnip rape and/or oilseed rape. Twenty-five (89%) of 28 children showed a positive challenge reaction to turnip rape. Seventeen reacted with labial whealing, and eight in oral challenge with facial urticaria, flare-up of AD or abdominal symptoms. All 25 control children remained negative in the labial challenge.
Conclusions: Turnip rape and oilseed rape seem to be new important food allergens in young children with AD. The modes of exposure to these allergens and the possible routes of sensitization remain to be established.
In western countries young children suffer frequently from food allergy and are often sensitized to multiple foods (1). Cow's milk, egg, wheat, peanut, fish and soy are the main allergenic foods in these children who mostly present with atopic dermatitis (AD) (2, 3). At Tampere University Hospital, for over 10 years, we have routinely performed skin prick test (SPT) screening with a large selection of commonly used foods in infants and young children with AD referred for the investigation of food allergy. Mustard (Sinapis alba) has been found to cause food allergies, especially in France (4, 5), which prompted us to include mustard in our SPT series. As the rate of sensitization was high, we included turnip rape (Brassica rapa) and oilseed rape (Brassica napus), which belong to the same Brassicaceae family as mustard, in the SPT series and found again a constant high number of positive SPT reactions.
Allergy to pollens of oilseed rape may occur (6) but, to our knowledge, food allergy to turnip rape or oilseed rape has not been previously described. Both plants are widely used in vegetable oil production. Oilseed rape ranks as the most commonly grown oilseed crop in Europe and turnip rape is particularly used by Finnish food industry (7).
In the present study we investigated by open food challenge with seeds of turnip rape whether children with positive SPTs to oilseed rape and turnip rape are also clinically reactive to these plants.
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Two hundred and six (10.9%) of the 1887 children screened had a clearly positive (≥5 mm) SPT to turnip rape (9.3%) or oilseed rape (9.4%). Eleven percent (149/1337) of the children under 3 years of age were sensitized to turnip rape and/or oilseed rape.
Twenty-five (89%) of the 28 children had a positive and three (11%) had a negative turnip rape challenge (Table 2). The labial challenge was positive in 17 (68%) children showing whealing and/or swelling. In addition, one child got rhinitis. The oral challenge was positive in eight children. Four of the children got immediate symptoms within <3 h and four others during the challenges at home. All 25 control children remained negative in the turnip rape labial challenge.
Table 2. Clinical types of challenge reactions to turnip rape in 25 children
| ||Positive challenge tests to turnip rape|
|Labial (n = 17)||Immediate oral (n = 4)||Delayed oral (n = 4)|
|Age, years, mean (range)|| 4 (1–9)|| 4 (1–10)|| 8 (5–15)|
|Oilseed rape ImmunoCAP (kU/l), median (range)||21.6 (0.70 to >100)||23.5 (2.19 to >100)||7.3 (0.90–16.30)|
|Skin prick test, wheal diameter (mm)|| || || |
| Turnip rape, median (range)|| 8 (5–23)|| 7 (6–9)|| 5 (4–8)|
| Oilseed rape, median (range)|| 7 (5–25)|| 7 (4–12)|| 5 (4–7)|
|Challenge|| || || |
| Dose (mg), median (range)||Small amount||500 (20–1350)||2700 (2700–6750)|
| Symptoms, n||Labial urticaria, 17 + rhinitis, 1||Facial urticaria, 2 Generalised erythema, 1 Abdominal complains, 1||Flare up of AD, 3* Flare up of asthma and abdominal complains, 1|
There was a clear correlation between the size of turnip rape and oilseed rape SPTs [0.69 (95% CI: 0.43–0.95)] in the 28 children challenged with turnip rape (Fig. 1). The SPT results to turnip rape and IgE antibody levels to oilseed rape in challenge-positive and challenge-negative children are given in Fig. 2A and 2B. At the time of challenge SPT reaction to turnip rape and oilseed rape had decreased <5 mm in two children, whereas in all the other children SPT was still clearly positive. The first child with a small SPT reaction showed flare up of AD, whereas in the second child the turnip rape challenge was negative. Only one of the 25 control children had IgE antibodies (2.1 kU/l) to oilseed rape. The total IgE was 1510 kU/l (median; 95% CI: 634–1790 kU/l) in the 25 challenge-positive children. In the three challenge-negative children, the total IgE was 26, 27 and 323 kU/l, respectively.
Figure 1. Skin prick test (SPT) reactivity to oilseed rape and turnip rape shows a significant [0.69 (95% CI: 0.43–0.95)] correlation in the 28 challenged children.
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Figure 2. (A) Skin prick test (SPT) reactivity and challenge test; (B) IgE antibody levels to oilseed rape and challenge reactions to turnip rape in 28 children.
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In the present study we found as high a prevalence as 11% of positive SPT reactions to turnip rape or oilseed rape in a cohort of 1887 Finnish children examined for suspected food allergy. Twenty-eight children with AD and positive SPTs to turnip rape and oilseed rape and 25 control children with AD and negative SPTs, respectively, participated in the open turnip rape challenge study. Most (89%) of the sensitized children showed positive labial or oral challenge reactions to turnip rape in contrast to none of the SPT-negative control children. The challenge reactions were mostly of immediate type such as labial swelling or facial urticaria. The dose of crushed turnip rape seeds causing positive oral challenge varied from 20 to 1350 mg. The large variation in the cumulative reactive doses correlates well with previous results in peanut and sesame seed challenge studies (12). Three challenge-positive children showed flare up of AD when the oral challenge had lasted for 2–5 days. Similar delayed type challenge reactions have been observed previously with cow's milk and wheat (13–15). When the 25 challenge-positive and three challenge-negative children were compared, the latter had smaller SPT reactions to turnip rape and oilseed rape and also lower IgE antibody levels to oilseed rape, suggesting a lower sensitization level to these plants. There was a tendency that younger children showed larger SPT reactions and immediate type responses to smaller amount of turnip rape seeds than older children, but the numbers of children in the variously reacting challenge groups were small.
Positive labial or oral challenges with turnip rape in the majority of the infants and young children with IgE antibodies to oilseed rape suggest that both of these oilseed plants could be clinically relevant food allergens. The observed high correlation in the SPT reactivity between oilseed rape and turnip rape suggests allergic cross-reactivity, supported also by recent finding of highly homologous 2S albumin allergens in both of them (T.J. Puumalainen, unpublished data). Interestingly, in France mustard allergy is now ranked fourth in children's food allergies (4) and a 2S albumin has been identified as a major allergen in mustard (Sinapis alba, Brassica juncea) (16, 17). Allergy to sesame (Sesamum indicum) has been reported to occur, e.g. in Israel and France and also seeds of this plant contain allergens belonging to the 2S albumin family (18, 19). Even low-grade consumption of mustard or sesame by the Finnish infants and young children seems unlikely because to our knowledge these agents are not added to commercial or home-made baby or children's food. In contrast, turnip oil is commonly used in the Finnish food industry and is included, e.g. in margarine and baby food (20). However, it remains to be settled whether biologically meaningful amounts of allergenic proteins are present in turnip rape or oilseed rape oils. In the present study we performed preliminary SPTs with refined and cold-pressed turnip oil in a few of the challenge-positive children, but all SPTs were negative (data not shown). It may be noted that cold-pressed and refined oils, such as peanut and sesame oil, have been reported to cause allergic reactions in highly sensitized individuals (12, 21), which implies that extended studies in this field are warranted.
In conclusion, turnip rape and oilseed rape are potentially important allergens in infants and young children. An oral route seems obvious for sensitization, but the food sources and clinical consequences of this new allergy are challenges for future research.