Résumé : Exacerbations are a main feature of asthma. The majority is associated with viral infections. Innate and adaptive immunity play a major role in the antiviral response, and also in allergy. The principal actors in innate immunity include bronchial epithelial and dendritic cells. They express host pathogen receptors (Toll-like receptors, RNA helicases), which recognize motifs present on the infectious agents. Recent work suggests the existence of special features of the innate immune response, which could favor the development and subsequent expression, and evolution of asthma and allergy. If they do exist, these special features could favor repeated asthma exacerbations. This hypothesis might allow the identification of a group of patients having a particular asthma phenotype, characterized by frequent exacerbations. © 2010 Elsevier Masson SAS. All rights reserved.