Allergen description
No allergens from this plant have yet been fully characterised.
A 32 kDa IgE-binding protein, a class I chitinase closely resembling the major Avocado allergen Prs a 1, has been isolated. This reactive component was strongly induced by ethylene treatment. Immunoblot inhibition assays demonstrated cross-reactivity between the 2 allergens. The purified allergen, designated PvChI, induced positive skin prick test responses in 7 of 8 patients with Latex-fruit allergy. This allergen was completely inactivated by heating (1).
Green bean probably contains heat-labile and heat-stable allergens. A 35 kDa protein, probably a novel allergen and not a chitinase, was detected in a 20-year-old girl who experienced anaphylaxis to Green bean. She reacted to boiled Green bean, which induced a stronger reaction than raw Green bean (2). That some allergens are differently sensitive to heat was demonstrated in a second study, in which boiling completely abolished skin reactivity (3). In 3 women who developed asthma and rhinitis after exposure to raw Green beans, but who tolerated ingestion of cooked Green beans, immunoblots of raw and cooked Green bean extract showed 2 IgE-binding bands with apparent molecular weights of 41.1 and 70.6 kDa. A 47 kDa IgE-binding protein was detected only in raw Green bean extracts (4).
A common feature of most legume allergens is their natural resistance to thermal, chemical, and, in some respects, proteolytic denaturation (5).
Potential Cross Reactivity
An extensive cross-reactivity among the different individual species of the genus could be expected but in fact does not occur frequently (6). In an in vitro study, the specific IgE binding by protein extracts of 11 food legumes was examined by IgE antibody determination and RAST inhibition. Cross-allergenicity was demonstrated to be frequent, and most marked between the extracts of Peanut, Garden pea, Chick pea, and Soybean (7). However, clinical studies have found that there is little cross-reactivity between members of the legume family (8-10).
Nevertheless, legumes are an important ingredient in the Mediterranean diet, and 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. A high degree of cross-reactivity has been demonstrated among Lentil, Chick pea, Pea and Peanut. Unlike in other populations, in Spanish children this phenomenon implies clinical sensitisation for many. In a study of 39 Spanish children challenged (open or simple blind) with 2 or more legumes, 82% reacted to 2 or more legumes: 43,5% to 3, 25,6% to 2, and 13% to 4 legumes. However, and surprisingly, the legumes White bean and Green bean and Soy were well tolerated by children allergic to other legumes. Therefore the diagnosis of legume allergy should not be based only on allergen specific IgE tests (11).
PvChI, a class I chitinase closely resembling the major Avocado allergen Prs a 1, was demonstrated through immunoblot inhibition assays to be cross-reactive (1).
A study investigated the in vitro cross-reactivity of allergens from Mesquite tree pollen (Honey Locust tree; Prosopis juliflora) and Lima bean (Phaseolus limensis/Phaseolus lunatus). Of 110 patients with asthma, rhinitis or both, as evaluated with intradermal skin test, 20 were highly positive to Mesquite pollen extract. Of these, 12 patients showed elevated IgE antibody levels to Mesquite pollen extract alone, and 4 to both Lima bean and pollen extract. Lima bean extract could inhibit IgE binding to Mesquite in a dose-dependent manner. Also, humoral and cellular cross-reactivity was demonstrated (12). Although cross-reactivity was not investigated between Mesquite and Green bean per se, cross-reactivity may exist between pollen from this tree and other species of Phaseolus.
