Molecular, structural, and immunologic relationships between different families of recombinant calcium-binding pollen allergens.

Abstract

Calcium-binding plant allergens can be grouped in different families according to the number of calcium-binding domains (EF hands). We sought to identify pollens containing crossreactive calcium-binding allergens and to investigate structural and immunologic similarities of members belonging to different families of calcium-binding allergens. By means of multiple sequence alignment and molecular modeling, we searched for structural similarities among pollen allergens with 2 (Phl p 7, timothy grass; Aln g 4, alder), 3 (Bet v 3, birch) and 4 EF hands (Jun o 4, prickly juniper). Purified recombinant Aln g 4 and Jun o 4 were used to determine the prevalence of IgE recognition in 210 patients sensitized to different pollens and to search, by means of ELISA competition, for the presence of cross-reactive epitopes in pollens from 16 unrelated plant species. IgE cross-reactivity among the allergen families was studied with purified rPhl p 7, rAln g 4, rBet v 3, and rJun o 4 and 2 synthetic peptides comprising the N-terminal and C-terminal EF hands of Phl p 7 by means of ELISA competition. Structural similarities were found by using molecular modeling among the allergens with 2, 3, and 4 EF hands. Pollens from 16 unrelated plants contained Aln g 4- and Jun o 4-related epitopes. Twenty-two percent of the patients with multiple pollen sensitization reacted to at least one of the calcium-binding allergens. A hierarchy of IgE cross-reactivity (rPhl p7 > rAln g 4 > rJun o 4 > rBet v 3) could be established that identified rPhl p 7 as the EF-hand allergen containing most IgE epitopes in the population studied. The demonstration that members of different families of calcium-binding plant allergens share similarities suggests that it may be possible to use representative molecules for the diagnosis and therapy of allergies to EF-hand allergens.