Leek (Allium porrum) is a widely cultivated and consumed vegetable. It belongs to the Liliaceae family, which includes onion (A. cepa), garlic (A. sativum), and asparagus (A. officinalis).
Members of the Liliaceae family can be potent contact allergens for people handling them in large amounts (1, 2). They also can cause IgE-mediated occupational diseases (3–5). Leek is sometimes mentioned as a cross-reactive allergen, but it has never been described as the main allergenic source.
Patient J.D., a 26-year-old woman, presented with asthma and eczema. She had been harvesting and handling leek for 3 years. She had no history of atopy. Some months after having started this work, she began to complain of conjunctivitis, rhinitis, asthma, and eczema on the hands. She could not remember having allergic reactions to any other vegetable than leek.
Pulmonary function tests revealed broncho-obstructive lung disease with a forced vital capacity of 3130 ml (98% of normal) and a FEV1 of 1950 ml (70% of normal value), values which returned to normal after treatment with inhaled corticosteroids (fluticasone) and short acting β2-agonists. Blood tests revealed increased eosinophilia (820/mm3).
Skin prick tests with commercial allergen extracts of grass-pollen mixture, tree-pollen mixture, weed pollen, Dermatophagoides, molds, latex, and cat and dog dander were negative. Specific IgE to latex, mugwort, dandelion, English plantain, goosefoot, and nettle was also negative.
A prick-prick test with raw leek leaf and leek bulb, followed by a scratch test with a piece of leek leaf or bulb, resulted in immediate local reactions of more than 10 mm with pseudopods, which were greater than with the negative control. A patch test with leek leaf, read at 48 h, was positive, while a patch test with the European Standard Series of contact allergens was negative.
Proteins were extracted from leek leaf, garlic cloves, and onion bulb, by the method of Rudeschko et al. (6). Cooked leek was prepared by boiling leek in distilled water. Proteins were then extracted from the cooked pieces as mentioned. The liquid phase was also kept and concentrated 10-fold.
The Coomassie brilliant blue-stained SDS–PAGE leek protein pattern displayed a high number of bands. The onion and garlic patterns were different from that of leek, and from each other. In cooked leek (liquid and solid phase), a great number of bands disappeared, as compared with raw leek extract. However, some proteins were temperature-resistant. In SDS–PAGE immunoblots, patient J.D.'s serum IgE reacted with a unique band at 41 kDa of the raw leek extract. It did not recognize any band in the onion and garlic extract. The two extracts from cooked leek showed no reactivity either, suggesting that this 41 kDa allergen might be temperature-sensitive.
The peculiarity of the present case is that the patient did not show any sign of common inhalant allergies, nor was there cross-reactivity with the closest botanically related vegetables, namely onion and garlic. The patient presented with contact eczema on handling leek, and the patch test with leek was positive. Because proteins of a high molecular mass, such as the one at 41 kDa, are not likely to penetrate the intact epidermis, another pathomechanism involving smaller components of leek must be held responsible for the cutaneous reactions. Diallyl disulfide in garlic, and allyl isothiocyanate in onion are two such small molecules that are known to induce type IV hypersensitivity (2).
This report documents the possibility of occupational sensitization and IgE reactivity to leek in the absence of sensitization to common inhalant allergens. Despite the high number of people handling or consuming leek worldwide, this allergy is not a major concern. However, the potential of leek as an occupational allergen must be kept in mind.