Figure 2.

Factors in the development of an exacerbation involve interactions with an environmental agent, respiratory virus, and host (genetics) factors to promote airway inflammation and lead to an exacerbation. In the susceptible asthma patient, a respiratory virus infects airway epithelium to activate an inflammatory response, which is characterized by eosinophils. This occurs early in the infection. This shifts the imbalance in asthma between inflammation to protection towards greater inflammation and a progression to an exacerbation. There is a later onset counterbalance with the production of antiviral interferons, which may gradually control the viral infection.