Allergen description
The following allergens have been categorised:
- Len c 1, a 12 to 16 kDa protein, a major allergen, corresponding to gamma-vicilin storage proteins (1-5).
- Len c 2, a 66 kDa protein, corresponding to seed-specific biotinylated protein (1-2).
- The isoforms Len c 1.0101, Len c 1.0102, Len c 1.0103 and Len c 2.0101 have been characterised.
Both Len c 1 and Len c 2 have been isolated from boiled Lentils. Heat treatment of Lentils was shown to result in drastic changes in the electrophoretic pattern, a strong increase of low-molecular-weight bands of 12 to 16 kDa proteins, and a decrease or disappearance of protein bands in the 25 to 45 kDa range. Len c 1 was shown to bind to 68% of the individual sera of Lentil-allergic individuals tested, whereas Len c 2 reacted with 41% of individual sera of this group (1).
Len c 1.01, a 48 kDa protein, has been characterised. Two of its processing fragments, corresponding to subunits of 12 to 16 kDa (previously named Len c 1) and 26 kDa, were shown to also be relevant Lentil IgE-binding proteins. The purified allergen was recognised by 77% (17/22) of the individual sera from patients with Lentil allergy. Three isoforms were isolated, varying in their degree of N-glycosylation. There was a greater than 50% amino acid homology with Peanut and Soy vicillins (5).
Although many legumes appear to have both heat-labile and heat-stable allergens, a common feature of most legume allergens is their natural resistance to thermal, chemical, and, in some respects, proteolytic denaturation (6). The process of heating results in a significant decrease in IgE antibody binding, and IgE inhibition studies showed that the boiled Lentil extract had a greater inhibitory capacity than the crude extract. Immunoblots revealed no important differences in IgE binding patterns between the 2 extracts. Multiple allergens have been detected in a wide range of molecular mass, and boiled Lentil extracts maintained strong allergenicity (7). But further evidence for the heat alteration of the allergenicity was demonstrated in studies that concluded that Lentil extracts for the diagnosis of Lentil hypersensitivity should be heated, since these best identify clinically sensitive individuals (8).
Lentil-allergic patients who had developed a tolerance to Lentil ingestion were shown to have lower IgE antibody levels than symptomatic patients (7).
A lipid transfer protein has been isolated from germinated Lentil seed (9). Its potential allergenicity was not evaluated.
Potential Cross Reactivity
An extensive cross-reactivity among the different individual species of the genus could be expected but in fact is not seen frequently (10). In an in vitro study, the IgE antibody binding by protein extracts of 11 food legumes was examined by IgE antibody determination and RAST inhibition. Cross-allergenicity was demonstrated to be immunochemically frequent, and most marked between the extracts of Peanut, Garden pea, Chick pea, and Soybean (11). However, clinical studies have found that there is little cross-reactivity among members of the legume family (12-14).
In contrast with the typical diet of most other Western countries, legumes are an important ingredient in the Mediterranean diet, and it is therefore not surprising that among Spanish children, sensitivity to legumes is the fifth most prevalent food allergy. Lentil and Chick pea are the most frequent causes of allergic reactions to legumes in Spanish children. Legumes have structurally homologous proteins, but they are not all equally allergenic. In vitro and in vivo tests may not predict cross-reactivity or clinical relevance. In a study of 39 Spanish children challenged (open or simple blind) with 2 or more legumes, the majority had symptoms with more than 1 legume. Thirty-two (82%) reacted to 2 or more legumes: 43,5% to 3, 25,6% to 2, and 13% to 4 legumes. Seventy-three per cent of the patients challenged with Lentil and Pea had positive challenges to both, 69,4% to Lentil and Chick pea, 60% to Chick pea, and 64,3% to Lentil, Chick pea and Pea simultaneously. Peanut allergy can be associated with allergy to Lentil, Chick pea and Pea, but less frequently. In contrast, White bean, Green bean and Soy were well tolerated by children allergic to other legumes. A high degree of cross-reactivity appeared to exist among Lentil, Chick pea, Pea and Peanut, on evidence from inhibition experiments. In this study, 82% of the children allergic to legumes were also sensitised to pollen. Pea and Bean were more likely to have in vitro cross-reactivity with Lolium perenne, Olea europea and Betula alba; the authors suggested that this was a result of common antigenic determinants or the coexistence of pollen and legume allergy (15).
Similarly, in another Spanish study, symptomatic hypersensitivity to Chick pea was frequently associated with Lentil allergy (16). Cross-reactivity or co-sensitivity was also observed among Blue vetch (Chickling pea), Chick pea, and Lentil (17). Similarly, shared allergenicity has been shown among blackgram, Lentil, Lima bean and Pea (18).
Panallergens or common protein families (e.g., vicilins) may result in cross-reactivity among foods. Amino acid sequences deduced from 2 clones of the Lentil allergen Len c 1.02 were shown to have greater than 50% identity with the major Peanut allergen Ara h 1, and with Soybean (conglutinin subunits), which are allergens belonging to the vicilin family (5). Similarly, in a study of 18 Spanish patients with Pea allergy, allergic reactions to ingestion of Pea were frequently associated with Lentil allergy. Vicilin and convicilin were shown to be potential major allergens from Pea, and these cross-reacted with the major Lentil allergen Len c 1 (4). Similarly, analysis of the epitopes and vicilin allergens Ara h 1 from Peanut, Len c 1 from Lentil, and Pis s 1 from Pea were shown to be similar, readily accounting for the IgE-binding cross-reactivity commonly observed among the vicilin allergens from these edible legume seeds (3).
