Viral infection and asthma: Respiratory syncytial virus and wheezing illness

A strong link between bronchiolitis and asthma has been indicated. Bronchiolitis that occurs in infants is manifested physiologically by a widespread narrowing of the air passages and, clinically, by asthma-like symptoms.The major cause of bronchiolitis is respiratory syncytial virus infection. While the precise pathophysiologic sequences of infection are incomplete, many observations have suggested that there is an infiltration of eosinophils in the airways. Current studies have shown that the respiratory syncytial virus penetrates the pulmonary defenses and initiates immunologic responses. The histamine and leukotriene mediators that are released produce an inflammatory reaction and the chemotactic factors bring eosinophils to the site of the reaction. Degranulation of eosinophils can release eosinophil cationic protein into the airways. Our finding that chemoattractants for eosinophils, interleukin-8 and RANTES (regulated upon activation, normal T cell expressed and presumably secreted) were detected in nasopharyngeal aspirates of infants with bronchiolitis suggests that such chemokines from epithelial cells may induce an eosinophil infiltration in the airway. Similar allergic inflammatory changes have been observed in asthma and in epithelial cells infected with respiratory viruses. Future investigation of the mechanism by which bronchiolitis can induce asthma will provide benefits in the treatment and prevention of asthma in sensitive individuals.