Rhinovirus-Induced Exacerbations of Asthma and COPD

Hershenson, Marc B.

Respiratory viral infections cause exacerbations of asthma and COPD. This is evidenced by the increased identification of viruses in the respiratory tract during exacerbations compared to stable periods. Also, epidemic cycles of asthma and COPD exacerbations occur after school return and around the Christmas holiday, consistent with an infectious cause. It has also been well demonstrated that viruses infect and replicate in the lower airways. Finally, the severity of viralinduced exacerbations correlates with viral load. Viral infection of the epithelium increases expression of chemokines, leading to influx of inflammatory cells and increased airway inflammation. Innate immunity to viral infection may be decreased in asthma, owing to epithelial damage, mucus metaplasia, and immune system polarization towards a Th2 phenotype. Disease exacerbation in asthmatics (rather than a simple cold) may be explained in part by infection of airway inflammatory cells, which are increased in patients with preexisting airways disease. As with asthma, viralinduced COPD exacerbations are associated with increased 8 Scientifica airway neutrophils, eosinophils, and lymphocytes. Patients with COPD demonstrate clear evidence of impaired antiviral innate immune responses. Finally, in COPD, viral infection may suppress antibacterial responses and increase translocation of bacteria across the airway epithelium, leading to exacerbation and perhaps disease progression.