Asthma, viruses, and nitric oxide.

Over the last two decades there has been a worldwide increase in the morbidity and mortality associated with asthma, a chronic inflammatory disease of the airways. There is a growing body of evidence that suggests there is an association between upper respiratory viral infections, particularly rhinovirus infections, and asthma exacerbations. Virally induced airways hyperreactivity has been associated with elevated numbers of inflammatory cells in the bronchial mucosa. Upon virus infection, respiratory epithelial cells produce proinflammatory cytokines, including IL-6, IL-8, RANTES, and GM-CSF, which could contribute to the increased inflammatory cell recruitment noted in the airways. Whether or not a viral infection triggers an asthma attack may depend upon many factors, including the types of inflammatory cells recruited to the airways, the viral load, and variations in the host antiviral response. There is evidence to support the idea that eosinophils from asthmatic and symptomatic atopic subjects may be primed to respond to chemotactic cytokines produced by infected epithelial cells. Rhinovirus infections may therefore enhance airway eosinophilia in asthmatics, leading to airway hyperresponsiveness and impaired pulmonary function. Nitric oxide is a potent inhibitor of both rhinovirus-induced cytokine production and viral replication and may play an important role in the host response to viral infections. Based upon these observations, we speculate that nitric oxide donors may represent a novel therapeutic approach for the treatment of rhinovirus infections and viral exacerbations of asthma.