Combined sensitization of mice to extracts of dust mite, ragweed, and Aspergillus species breaks through tolerance and establishes chronic features of asthma.

BACKGROUND: Existing asthma models develop tolerance when chronically exposed to the same allergen.
OBJECTIVE: We sought to establish a chronic model that sustains features of asthma long after discontinuation of allergen exposure.
METHODS: We immunized and exposed mice to a combination of single, double, or triple allergens (dust mite, ragweed, and Aspergillus species) intranasally for 8 weeks. Airway hyperreactivity (AHR) and morphologic features of asthma were studied 3 weeks after allergen exposure. Signaling effects of the allergens were studied on dendritic cells.
RESULTS: Sensitization and repeated exposure to a single allergen induced tolerance. Sensitization to double and especially triple allergens broke through tolerance and established AHR, eosinophilic inflammation, mast cell and smooth muscle hyperplasia, mucus production, and airway remodeling that persisted at least 3 weeks after allergen exposure. Mucosal exposure to triple allergens in the absence of an adjuvant was sufficient to induce chronic airway inflammation. Anti-IL-5 and anti-IL-13 antibodies inhibited inflammation and AHR in the acute asthma model but not in the chronic triple-allergen model. Multiple allergens produce a synergy in p38 mitogen-activated protein kinase signaling and maturation of dendritic cells, which provides heightened T-cell costimulation at a level that cannot be achieved with a single allergen.
CONCLUSIONS: Sensitivity to multiple allergens leads to chronic asthma in mice. Multiple allergens synergize in dendritic cell signaling and T-cell stimulation that allows escape from the single allergen-associated tolerance development.