Biochemical and Immunological Characterization of Pollen-Derived β-Galactosidase Reveals a New Cross-Reactive Class of Allergens among Mediterranean Trees

Abstract

Background: The most potent allergens in the Spermatophytae family exhibit significant homology with enzymes. Some of these are though to be involved in pectin metabolism, recognition of compatible stigma and delivery of sperm cells to the ovule. Objective: To test if glycohydrolase activities from some Mediterranean tree pollens could act as allergens in sensitized hosts. Methods: Freshly collected Cupressus and Olea pollens were investigated for their glycohydrolase activities by means of synthetic fluorogenic substrates and isoenzymes characterized by DEAE-cellulose ion-exchange chromatography. Binding of specific IgE was investigated by immunoblotting in 30 tree-sensitive subjects, as well as in 20 atopic non-tree-sensitive and 15 healthy controls. The enzymes were also adopted to stimulate proliferation of allergen-specific T cell clones. Finally, they were tested in vivo in a cutaneous immediate wheal and flare reaction. Results: β-Galactosidase (β-GAL) is present with different isoenzymatic patterns on both pollen extracts, could be recognized by circulating IgE, as well as immunoprecipitated by sera from allergic subjects. The enzyme could stimulate the proliferation of T cells from allergic subjects, and favor the emergence of CD4+ T cell clones with specific in vitro reactivity to β-GAL. Finally, the enzyme induced in vivo a cutaneous wheal and flare reaction in clinically sensitive subjects. Conclusions: Despite different isoenzymatic patterns, Olea-derived β-GAL cross-reacted with that from cypress pollen, suggesting that these enzymatic glycoproteins may represent major native allergens among these Mediterranean trees.