False-positive skin prick test responses to commercially available dog dander extracts caused by contamination with house dust mite (Dermatophagoides pteronyssinus) allergens

Background: In an outpatient population, a high frequency of positive skin prick test responses to dog dander was found in the absence of detectable IgE to dog dander in the RAST The majority of these patients were sensitized to house dust mites (Dermatophagoides pteronyssinus) and had no obvious dog-related allergic symptoms. These findings prompted us to investigate whether dog dander skin test preparations are contaminated with house dust mite allergens in amounts sufficient to cause false-positive skin prick test responses in patients sensitized to house dust mites. Methods: Antigen detection assays with monoclonal and polyclonal antibodies were rued to determine concentrations of the major allergen Can f 1 from dog dander and the major allergens Der p 1 and Der p 2 from house dust mites in five commercially available dog dander skin prick test preparations (A to E). Results: Can f 1 concentrations varied for the different extracts (A: 170 mu g/ml B: 11.1 mu g/ml, C: 13.3 mu g/ml, D: 3.8 mu g/ml, and E: 59.4 mu g/ml). Der p 1 was detectable in all extracts (A: 33.4 ng/ml, B: 5.1 ng/ml, C: 29.6 ng/ml, D: 0.4 ng/ml, and E: 1.9 ng/ml), and Der p 2 was detectable in some of the commercially available dog dander skin prick test preparations rested (A. 31.3 ng/ml, B: 3.0 ng/ml, and C: 7.5 ng/ml). The median house dust mite threshold in the skin prick test was found to be 5.8 ng/ml of Der p 1 (range, 3.5 to 20.8 ng/ml) in nine patients rested. Conclusion: Contamination of commercially available dog dander skin pride test preparations with the major allergens (Der p 1 and Der p 2) of the house dust mite (D. pteronyssinus) was demonstrated. These contaminations cause false-positive responses to skin prick tests with dog dander in patients sensitized to house dust mite.