Risk levels for mite allergens. Are they meaningful?

Allergens found in house dust are among the most common environmental antig ens to which man is naturally exposed. Standardized methods for measuring a llergen exposure are essential for assessing the relationship between expos ure, sensitization, and the severity of asthma. Monoclonal antibody-based a ssays are the most widely used method for assessing allergen exposure. In t he effort to define the best "index of exposure" to mite allergens, several factors need to be investigated, including: 1) whether allergen should be measured in reservoir dust or airborne 2) whether the results of reservoir measurement should be expressed as reco vered allergen per unit weight or per unit area. As yet, airborne sampling is insufficiently sensitive to produce reliable a nd repeatable results. Therefore, measurement of house-dust-mite allergen c oncentration in reservoir dust should be regarded as the best-validated ind ex of exposure. The results should be expressed and reported both per unit weight (concentration) and per unit area. The strongest predictor of chroni c symptoms and acute exacerbation of asthma is sensitization to indoor alle rgens. A simple dose-response relationship between IgE-mediated hypersensit ivity and allergen exposure has been established. For example, exposure to more than 2 mu g Group 1 mite allergen/g dust should be regarded as a risk factor for the development of IgE antibody and asthma in susceptible childr en. The quantitative relationship between exposure and symptoms in patients already sensitized is complex due to a number of possible confounding fact ors (e.g., other allergens, viruses, asthma medication). A simple threshold level for provocation of asthmatic symptoms has not been clearly defined.