Scientists at Washington University School of Medicine in St. Louis have implicated a type of immune cell in the development of chronic lung disease that sometimes is triggered following a respiratory viral infection. The evidence suggests that activation of this immune cell—a type of guardian cell called a dendritic cell—serves as an early switch that, when activated, sets in motion a chain of events that drives progressive lung diseases, including asthma and chronic obstructive pulmonary disease (COPD).