Development of a Method to Evaluate Cat Dander Levels by Safranin-O Staining

RATIONALE: Cat dander is a potent indoor allergen and Feld1 is primarily responsible for allergic symptoms. However in a cat challenge chamber, which replicates home exposure, Feld1 levels can vary tremendously over time making it difficult to assess patient exposure on different days. ELISA assays for Feld1 delay ability to regulate levels in sufficient amount of time. Our purpose was to determine if dander counting by staining and light microscopy correlated to Feld1 measured by ELISA would allow prompt measurements and tighter control on allergen levels.

METHODS: Dander samples were obtained after shaking the cat’s bedding for 1 minute in a central area of the room. Dander was collected on filters in petri dishes on the floor of the cat-chamber or by wiping surfaces with a moistened filter. Glass fibre and isopore filter types were used for testing. Staining was done with four concentrations of Safranin-O (0.1, 0.01, 0.05% and 0.001%). For each concentration, three staining times were also tested. Dander particles were counted using light microscopy.

RESULTS: Safranin-O 0.01% stained optimally, as it provided a differential contrast between dander particles and the filter background by staining dander red/pink. The optimum staining time was 60 minutes. Although isopore filters visualized dander more clearly, they tended to fold and not absorb stain completely, causing distortion and bubbles under the microscope. Glass fibre filters absorbed stain well, however, background fibers made it challenging to visualize dander.

CONCLUSIONS: The results of this study may prove useful in ensuring more stable allergen concentrations in cat challenge chambers.