The NPC2 protein: A novel dog allergen.

BACKGROUND: Dogs are an important source of indoor allergens that cause rhinoconjunctivitis, urticaria, and asthma in sensitized individuals. Can f 1 is reported as a major dog allergen, but other allergens have also been identified. Identification of immunologically important allergens is important for both the diagnosis and treatment of dog allergy. OBJECTIVE: To identify and characterize the canine NPC2 protein, a novel dog allergen. METHODS: We screened commercial and laboratory-generated aqueous dog extracts by 2-dimensional polyacrylamide gel electrophoresis with IgE immunoblotting using human serum samples from 71 dog-allergic individuals. A target of interest was excised from the gel and sequenced. Canine NPC2 sequence was generated, and recombinant proteins expressed in yeast and bacteria were used to determine allergenicity. An IgE enzyme-linked immunosorbent assay was used for screening 71 dog-positive and 30 dog-negative serum samples. RESULTS: A 16-kDa protein (pK = 8.5) in dog allergen extracts was recognized by specific IgE. The protein was identified by sequencing as a CE1 protein or NPC2 protein. Human IgE bound to recombinant protein was expressed in both yeast and bacteria. Ten (14%) of 71 individuals had specific IgE to NPC2 protein from bacteria, and 12 (17%) had IgE to NPC2 protein from yeast. Binding of pooled dog-allergic serum IgE to the dust mite protein Der p 2 was partially inhibited by recombinant NPC2 protein. CONCLUSION: NPC2 protein, a member of the MD-2-related lipid recognition family, is identified as a dog allergen (Can f 7), with an apparent seroprevalence of 10% to 20%.