Airborne allergens associated with asthma: Particle sizes carrying dust mite and rat allergens measured with a cascade impactor

Abstract

Patients with asthma may develop acute symptoms after exposure to domestic or laboratory animal allergens; however, they are usually not aware of a direct relationship between their acute attacks and exposure to pollen or dust mite allergens. The present experiments were designed to study whether the differences in symptoms could be explained by differences in the number or size of particles carrying airborne allergens. Airborne particles were collected with a filter or on the stages of a cascade impactor, and allergens were measured by use of inhibition radioimmunoassays. In rat rooms and during disturbance of rat liner, a large proportion of rat urinary allergen (45.9%) was collected on the second stage of the impactor (mean size ∼7 μm diameter). When sampled 15 to 35 minutes after disturbance, 16% of these medium-sized particles were still airborne. By contrast, during disturbance of house dust, a significantly larger proportion of dust mite, antigen P 1 (80.6 ± 11.8%; p < 0.001) was collected on the first stage of the impactor, and in keeping with the apparent size of these particles (diameter >10 μm), very little of this allergen (<4%) was still airborne when sampled 15 to 35 minutes after disturbance. With nebulized diluted rat urine, ∼75% of the allergen was collected on the fourth and final stages of the cascade impactor in keeping with the expected size, 0.5 to 3 μm in diameter. These results demonstrate that natural exposure to both allergens is strikingly different from the conditions used for bronchial provocation. The results suggest that the different clinical responses may be explained by differences in the size of the particles on which these two allergens become airborne.