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Identification and characterization of Lyc e 4, a Bet v 1 homologous PR-10 protein, in tomato fruits
© Jamin et al; licensee BioMed Central Ltd. 2013
Published: 25 July 2013
Allergy to tomato (Lycopersicon esculentum) has been reported to occur in 3-16% of food allergic subjects. Tomato allergy is frequently manifested as OAS, urticaria and gastrointestinal symptoms. So far, three tomato allergens, Lyc e 1 (profilin), Lyc e 2 (invertase) and Lyc e 3 (nsLTP) are listed in the official IUIS allergen database. Although tomato allergy is frequently associated with birch pollen allergy in Central Europe, a cross-reactive Bet v 1 homologous allergen has not yet been described in tomato fruits. The objective of the present study was the cDNA cloning, recombinant expression and immunological characterization of Bet v 1 homologous PR10-proteins from tomato fruits.
Two Bet v 1 homologous PR10 cDNA sequences (designated Lyc e 4a and Lyc e 4b) from tomato fruit (cv Verona) were cloned by RT-PCR and 5'RACE. Lyc e 4 proteins were expressed in E. coli and purified under native conditions by Ni-NTA chromatography. Purity and secondary structure of the protein were analyzed by SDS-PAGE and CD spectroscopy. Allergen-specific IgE levels to tomato, birch pollen, rBet v 1 and rLyc e 4a were measured by ImmunoCAPTM in birch pollen allergic patients with a clinical history of allergy (n=45) or tolerance (n=26) to tomato.
Lyc e 4a (Acc.No. AK224718) and Lyc e 4b (Acc.No. AK247106) showed 81% amino acid identity (aa-id) to one another and 42% and 44% aa-id to Bet v 1 (Acc.No X15877), respectively. Among PR-10 allergens from other species, the two Lyc e 4 isoforms showed highest aa-id (52% and 51%) with Pru ar 1 from apricot. Both recombinant proteins displayed secondary structures similar to those of Bet v 1. Tomato-specific IgE was detectable in 67% (30/45) of tomato/birch pollen allergic patients while 76% (34/45) showed IgE binding to Lyc e 4a and 78% (35/45) to Bet v 1. All birch pollen allergic but tomato tolerant patients displayed IgE to birch and Bet v 1, as well as to Lyc e 4a, despite their tomato tolerance. The IgE-reactivity to Lyc e 4a and Bet v 1 correlated strongly, even though we observed lower levels of IgE binding to Lyc e 4a.
According to the guidelines of the IUIS allergen nomenclature subcommittee, Lyc e 4 qualifies as major allergen in tomato fruits. Serological IgE testing with Lyc e 4 showed high sensitivity but low clinical specificity in this patient population. The clinical relevance of Lyc e 4 needs to be further evaluated.
Disclosure of interest
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.