Characterization of IgE epitopes of Cuc m 2, the major melon allergen, and their role in cross-reactivity with pollen profilins

Abstract

Background Plant profilins are described as minor allergens, although with some exceptions in foods such as melon, watermelon or orange. In fact, they could be responsible for many cross-reactions among distantly related species. This is likely to be a consequence of the presence of common epitopes. Objective To characterize the B epitopes of Cuc m 2, a model of plant food profilin, using phage display techniques and to compare with other profilins, such as those of timothy grass and birch pollen, and human I profilin, to understand the mechanism of cross-reaction among members of this family. Methods IgE of melon-allergic patients was used to select clones from a phage display 12 mer peptide library. After two rounds of screening, Cuc m 2-specific clones were eluted and the DNA insertion sequenced. The residues of each clone were mapped on the Cuc m 2 surface to define a mimotope, which was also localized on the three-dimensional surfaces of other profilins. Results Seventeen melon-allergic patients were selected. Sera from each of them recognized the melon profilin, Cuc m 2, but the majority also recognized Phl p 12 or Bet v 2, timothy grass-, and birch-pollen profilins, respectively. A Cuc m 2 mimotope was defined and mapped onto its surface giving the following sequence: S2W 3A5Y6D9H10T 111P112G113Q114N116M 117R121L122. The homologous residues in Phl p 12 and Bet v 2 had almost identical sequences. By contrast, the homologous sequence in human profilin showed many differences. Conclusions The identified mimotope could be involved in cross-reactions among food and pollen profilins. Many of these cross-reactions observed in the clinical realm could be explained by the presence of a common epitope found in food and pollen allergens. A new strategy of immunotherapy based on this IgE region could be used in alternative immunotherapy strategies. © 2009 Blackwell Publishing Ltd.