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

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: S(2)W(3)A(5)Y(6)D(9)H(10)T(111)P(112)G(113)Q(114)N(116)M(117)R(121)L(122). 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.