Lipophilic allergens: their isolation and clinical relevance

Introduction: Preliminary results on house dust mite allergens could associate lipophilic allergens with allergic asthma. The DZL-flag ship project “basic science” focuses on the effect of allergenic structure on allergenicity with particular emphasis on asthma development and molecular phenotyping. Peanut allergy in this regard serves as a model disease, since the lipid-rich fruit peanut induces severe, sometimes fatal allergic symptoms including bronchospasm. Oleosins, a class of highly lipophilic oil body proteins have been found to be triggers of severe allergic reactions to hazelnut and sesame. The aims of this study were isolation of the peanut oleosins and the assessment of their allergenicity in order to have tools for mechanistic research on sensitization and asthma development.

Methods: A comprehensive oleosin isolation procedure was established based on oil body extraction and subsequent step by step purification along with preparative electrophoresis. Oil body proteins were identified by N-terminal sequencing, peptide mass fingerprinting and homology search against databases. The IgE-binding potency of oleosins was evaluated by immunoblot analysis and basophil activation tests.

Results: Oleosins were isolated and purified from the complex lipophilic matrix of peanut. Mass spectrometry analysis identified eight peanut oleosins, ranging from 15.5 to 17.5 kDa, named Ara h 10, 11, 14 and 15. IgE binding to purified oleosins was observed in 30 of 47 sera from peanut-allergic patients by means of immunoblotting. IgE-dependent basophil activation was induced in vitro in a dose-dependent manner in peanut-allergic patients, but not in controls. Oleosin sensitization was observed exclusively in patients suffering from severe allergic reactions e.g. dyspnea, urticaria and anaphylactic shock.

Discussion: A novel strategy for the simultaneous isolation of the lipophilic peanut allergens, oleosins, was successfully established. Their allergenicity was demonstrated via immunoblot and basophil activation test. These early results provide some evidence that oleosins are associated with more severe allergic reactions.