Major characteristics of allergic asthma include airflow obstruction, inflammation of the airways and airway remodelling in response to inhaled allergens. Inhalation of environmental particles is harmless in some individuals; however, in allergic individuals, certain environmental particles are recognized as foreign allergens and cause an allergic airway reaction. This can result in increased sensitivity and reactivity of the airways, in which the airways of the asthmatic patient tighten and constrict in a process called airway hyperresponsiveness (AHR). Exposure to a multitude of indoor and outdoor allergens varies with the seasons and many people develop multiple allergies, such that concurrent exposure to more than one allergen can drastically enhance this allergic airway response. Most published models of allergic asthma explore responses to a single allergen. However, it is unlikely that humans are only exposed to a single allergen and the sustained asthmatic effects of concurrent exposure to multiple allergens are unknown.
To determine the effect of simultaneous exposure to multiple allergens, this study combines two chronic mouse models of allergen challenge. The authors evaluate the structural and functional consequences to the airway after chronic exposure to ovalbumin (OVA) and proteins derived from house dust mites (HDM), either in combination or independently. They did not see a significant difference in AHR between animals exposed to HDM and OVA in combination, or to each allergen alone, after a transient exposure. Consistent with this, airway inflammation markers and airway remodelling in mice exposed to the combination of HDM and OVA did not significantly differ from mice exposed to HDM or OVA alone. However, following chronic exposure, they find that mice exposed to HDM and OVA in combination exhibit greater sustained AHR compared with either HDM or OVA alone.
There is a combinatorial effect of chronic exposure to multiple allergens that elevates inflammation and airway remodelling. A greater effort towards limiting allergen exposure, including to common house dust mites, may prevent subsequent allergen-induced airway disease. Further study of the combinatorial effects of allergens in animals and humans should offer insight into the mechanisms that cause the airway inflammation that leads to AHR.
