Aeroallergeni e trofoallergeni: omologie e possibile ruolo patogenetico.

The cases of two subjects with a clinical history of cutaneous and respiratory manifestations are presented. One of them, a 26-year-old female, complained of intermittent asthma and several episodes of post-prandial, exercise-induced urticaria-angioedema. The other subject, a 5-year-old male child, suffered from rhinitis and frequent diffuse post-prandial pruritus. Both patients tested positive to in vivo and/or in vitro allergodiagnostic tests for some of the common aeroallergens and food allergens. Using prick tests, the woman tested positive to Compositae, Graminaceae, Dermatophagoides farinae, cereals, legumes, hazelnuts, and tomatoes, while the child tested positive to Graminaceae only. A search for specific serum IgE gave partly different results (positive for Graminaceae and wheat in the first case, and for Graminaceae, tomatoes, wheat and beans in the second). In both subjects, avoiding the suspected foods (in the first case, avoiding physical exercise after their ingestion) led to the complete and spontaneous remission of cutaneous clinical manifestations, which was confirmed at a 6-month follow up. The simultaneous onset of pollen-related and food-related clinical manifestations led us to hypothesize and verify the existence of known and/or potential cross-reactive allergens between the vegetable species to which each of the patients was sensitized. To test this hypothesis we compared all amino acid sequences of the fully characterized proteins of the pollens of Graminaceae against those of the aforementioned vegetable foods, using the BLAST (Basic Local Alignment Search Tool) software with a cut-off value of E<0.001. Assessment of potential allergenicity was made on the basis of the FAO/WHO criteria. Our results show that the food/pollen allergen Tri a 4 of Triticum aestivum (wheat) is nearly identical to some pollen allergens (group 4 allergens) of other Graminaceae, and that the allergen beta-expansin 1 in wheat is very similar not only to other Graminaceae, expansins but also to those of Lycopersicon esculentum (tomato) and Cicer anetinum (chick pea). These data support the hypothesis that, in our patients, all clinical manifestations observed could be due to cross-reactivity caused by allergenic protein(s) which have been phylogenetically preserved in different vegetal species and suggest the need for further investigation, for both a better knowledge of allergic phenomena and possible future consequences on therapy and prevention. On the basis of the cases discussed, the paper also gives an overview on potential usefulness, limits and perspectives of in silico research as a support to, and complement of the traditional and currently unreplaceable in vitro and in vivo experimental procedures.