IgE Reactivity of the Dog Lipocalin Allergen Can f 4 and the Development of a Sandwich ELISA for Its Quantification

PURPOSE Divergent results on the IgE reactivity of dog-allergic subjects to Can f 4 have been reported. The aim of this study was to evaluate the significance of Can f 4 in dog allergy and to develop an immunochemical method for measuring Can f 4 content in environmental samples. METHODS We purified the natural dog allergen Can f 4 from a dog dander extract by monoclonal antibody-based affinity chromatography and generated its variant in a recombinant form. Sixty-three dog-allergic patients and 12 nonallergic control subjects were recruited in the study. The IgE-binding capacity of natural Can f 4 and its recombinant variant was assessed by ELISA, immunoblotting, and skin prick tests (SPT). RESULTS Eighty-one percent of the dog-allergic patients showed a positive result to the immunoaffinity-purified natural Can f 4 in IgE ELISA, but only 46% in IgE immunoblotting. Respective results with the recombinant Can f 4 variant were 54% and 49%. SPT results reflected those obtained in ELISA and immunoblotting. The overall IgE reactivity of the immunoaffinity-purified natural Can f 4 was found to depend strongly on the integrity of the allergen's conformation. A sandwich ELISA based on monoclonal antibodies was found to be functional for measuring Can f 4 in environmental samples. CONCLUSIONS Can f 4 is a major allergen of dog together with Can f 1 and Can f 5. In combination with other dog allergens, it improves the reliability of allergy tests in dog allergy.