The minor house dust mite allergen Der p 13 is a fatty acid binding protein and an activator of a TLR2-mediated innate immune response

Background: The house dust mite (HDM) allergen Der p 13 could be a lipid-binding protein able to activate key innate signaling pathways in the initiation of the allergic response. We investigated the IgE reactivity of recombinant Der p 13 (rDer p 13), its lipid binding activities and its capacity to stimulate airway epithelium cells. Methods: Purified rDer p 13 was characterized by mass spectrometry, circular dichroism, fluorescence-based lipid binding assays and in-silico structural prediction. IgE binding activity and allergenic potential of Der p 13 were examined by ELISA, basophil degranulation assays and in-vitro airway epithelial cell activation assays. Results: Protein modeling and biophysical analysis indicated that Der p 13 adopts a β barrel structure with a predominately apolar pocket representing a potential binding site for hydrophobic ligands. Fluorescent lipid binding assays confirmed that the protein is highly selective for ligands and that it binds a fatty acid with a dissociation constant typical of lipid transporter proteins. The low IgE binding frequency (7%, n= 224) in Thai HDM-allergic patients as well as the limited propensity to activate basophil degranulation classifies Der p 13 as a minor HDM allergen. Nevertheless, the protein with its presumptively associated lipid(s) triggered the production of IL-8 and GM-CSF in respiratory epithelial cells through a TLR2-, MyD88-, NF-kB- and MAPK-dependent signaling pathway. Conclusions: Although a minor allergen, Der p 13 may, through its lipid binding capacity, play a role in the initiation of the HDM allergic response through TLR2 activation