Allergic and nonallergic interactions between house dust mite allergens and airway mucosa.

Asthma and allergy are extremely frequent diseases, affecting 5-10% and 30% of the population, respectively. The prevalence of asthma has increased in many developed countries, which may be due to several factors, including increased exposure to house dust mite (HDM) allergens. HDM to which humans are most frequently sensitized are Dermatophagoides pteronyssinus, Dermatophagoides farinae, and Euroglyphus maynei. These mites multiply in carpets, bedding and upholstered furniture in a hot and humid atmosphere. The allergens are digestive enzymes of the mites. Several epidemiological studies have shown that an increase in exposure to HDMs is associated with an increase in the prevalence of sensitization and asthma, whereas mite avoidance leads to a decrease in respiratory symptoms of sensitized asthmatic subjects. Sensitized subjects have specific immunoglobulin G and E (IgG and IgE) humoral responses, as well as proliferative T-cell responses to HDM allergens. Experimental exposure to HDM allergens induces bronchoalveolar inflammatory responses, that are characterized by the recruitment and activation of eosinophils, mastocytes, neutrophils, monocytes and lymphocytes. The cysteine protease activity of Der p 1 (a major allergen of D. pteronyssinus) has been shown to increase airway mucosal permeability, and may thereby contribute to the pathogenesis of airway inflammation and hyperresponsiveness by nonimmunological mechanisms. These epidemiological and experimental data support the recommendations for mite avoidance, especially in persons at high risk of developing asthma.