Methods: DC-SIGN-binding and -blocking assays were performed on human monocyte derived dendritic cells (DCs) using fluorescent-labeled extracts and anti-DC-SIGN antibody respectively. Using a recombinant DC-SIGN-Fc chimera, food protein extracts were tested for DC-SIGN-binding by ELISA and autoradiography. IgE immunoblotting was performed using pooled sera from food allergic subjects.
Results: Peanut agglutinin (PNA) was identified in DC-SIGN-autoradiographs by mass spectrometry. PNA specifically bound to DC-SIGN on DCs in a calcium dependent manner and induced the expression of activation markers CD80, CD83, CD86 and HLA-DR in vitro. A number of DC-SIGN-binding proteins in allergenic foods such as peanut, soy, tree nuts, egg and milk were discovered. Foods that generally do not induce allergic responses in humans such as pine nuts, chickpea and corn showed no binding to DC-SIGN. Several DC-SIGN-binding proteins show reactivity in serum IgE immunoblots. We have also identified novel non-IgE-binding proteins that interact with DC-SIGN.
Conclusions: We present a comprehensive report on characterization of DC-SIGN-binding proteins in common allergenic foods. We demonstrate that PNA, a minor peanut allergen, is a novel ligand for DC-SIGN. Further functional characterization of DC-SIGN-interacting molecules in food allergens may provide new openings in our understanding of the pathology of food allergy and even novel therapeutic targets.