Variable content of Fel d 1 variants in house dust and cat extracts may have an impact on allergen measurement.

BACKGROUND The major cat allergen, Fel d 1, is a tetrameric glycoprotein composed of 2 heterodimers. Polymorphisms in this allergen are well documented. Recent work shows that Fel d 1 samples can contain core fragments of variable immunoreactivity. OBJECTIVES Our objective was to compare Fel d 1 polymorphism in cat extracts and house dust, which is used as an indicator of allergen exposure and to understand how the combination of individual Fel d 1 variants can affect cat allergen measurement. METHODS Natural Fel d 1 allergens were water-extracted from house dust and from the chest area and anal sacs of a cat. Recombinant Fel d 1 was provided commercially. The samples were analyzed by immunoblotting; variants were isolated using gel electrophoresis and tested using enzyme-linked immunosorbent assay. RESULTS Four Fel d 1 variants of 40, 30, 19-21, and 14-16 kDa were consistently identified in Fel d 1 samples. Fel d 1 patterns found in house dust and the chest area wash were similar. Dimers were shown to be the major variant, while intact or truncated tetramers and core fragments were found in variable amounts. Intact and truncated dimers of Fel d 1 displayed similar antibody binding. Conversely, the intact tetramer-but not the core tetramer-was found to bind twice the antibody amount as the dimers and core fragments. CONCLUSIONS Despite a common pattern of Fel d 1 variants in cat extracts and house dust, variations in the tetramer-to-dimer ratio among samples may introduce major discordances in cat allergen measurements using immunoassays. Our findings indicate the need for further harmonization of allergen immunoassays.