[Legume cross-reactivity]

Abstract

Legumes are dicotyledonous plants belonging to the Fabales order. The main distinctive characteristic of which is their fruit (legumen, seeds contained in pods). This botanical order is formed by three families: Mimosaceae, Caesalpiniaceae and Papilionaceae or Fabacea. The Papilionaceae family includes the most important allergenic species: Lens culinaris (lentil), Cicer arietinum (chick-pea), Pisum sátivum (pea), Arachis hipogea (peanut), Phaseolus vulgaris (bean) y Glycine max (soy). Legumes are an important ingredient in the Mediterranean diet. Among Spanish children, sensitivity to legumes is the fifth most prevalent food allergy. Lentil and chick-pea are the most frequent cause of allergic reactions to legumes in Spanish children. Legumes could be involved in severe allergic symptoms. The different legumes have structurally homologous proteins, but they are not all equally allergenic, thus making it difficult to distinguish in vitro and in vivo cross-reactivity. We have demonstrated by skin tests and CAP that most of the patients are sensitised to more than one species. We have demonstrated a great degree of cross-reactivity among lentil, chick-pea, pea and peanut by ELISA inhibition (> 50 % max. inhibition). Unlike the Anglo-Saxons population, this phenomenon implies clinical sensitisation for many Spanish children. The majority of our patients have had symptoms with more than one legume (median 3 legumes). Thirty-nine patients were challenged (open or simple blind) with two or more legumes and 32 (82 %) reacted to two or more legumes: 43,5 % to 3, 25,6 % to 2, 13 % to 4 legumes. Seventy three per cent of the patients challenged with lentil and pea had positive challenge 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 peanut can be associated to allergy to lentil, chick-pea and pea but less frequently. Contrarily, white bean and overall green bean and soy are well tolerated by children allergic to other legumes. In our study, 82 % of the children allergic to legumes had a sensitisation to pollen. Pea and bean are the legumes with more in vitro cross-reactivity with Lolium perenne, Olea europea and Betula alba. This cross-reactivity could be because of common antigenic determinants or due to the coexistence of pollen and legume allergy. Panallergens implication seems to be less probable. It is important to emphasize that in spite of an evident clinical and immunological cross-reactivity, the diagnosis of legume allergy should not be based only on specific IgE tests. The decision to eliminate one legume from the diet should be based on a positive oral food challenge.