Identification of immunodominant IgE epitopes of the major house dust mite allergen Der f 24.

Previously, a ubiquinol‑cytochrome c reductase binding protein (UQCRB) homolog was identified in the house dust mite (HDM) species Dermatophagoides farinae (Der f) as a major allergen. In the present study, the immunodominant immunoglobulin E (IgE) epitope of the protein Der f 24 was investigated. Analysis of the homologous amino acid (aa) sequences in Der f and human UQCRB was performed. Four different recombinant Der f 24 and hybrid proteins formed by integrating Der f and human UQCRB sequences were expressed in Escherichia coli, purified using Ni‑NTA resins, and IgE‑binding activity was determined using IgE‑western blotting and enzyme‑linked immunosorbent assay (ELISA) experiments. IgE epitopes were further identified by IgE‑dot blotting and IgE‑ELISA with synthetic polypeptides and HDM‑allergic sera. Three‑dimensional (3D) structural modeling was used to analyze the position of the immunodominant IgE epitope. The amino acid sequence homology between Der f 24 and the human UQCRB protein was determined to be 39.34%. IgE‑ELISA and western blot analysis showed that all of the Der f‑human UQCRB hybrid proteins generated, except for the one lacking 59 residues of the N‑terminal region of Der f 24, were bound by allergic serum IgE. A synthetic polypeptide consisting of 32 residues of the N‑terminal reacted with IgEs from HDM‑allergic sera and could be used to generate high titer specific IgG or specific IgE antibodies in immunized mice. The 32‑aa N‑terminal region of Der f 24 was localized to a structural protrusion, which may facilitate specific IgE‑binding. These results indicate that the immunodominant IgE epitope of Der f 24 is located mainly in a 32‑residue region of the N‑terminus. These findings may inform the mechanisms of HDM allergy sensitization and allergy immunotherapy development.