title: Role of respiratory viral infections in the development of atopic conditions.
abstract: OBJECTIVE
  Respiratory viral infections are implicated in both protection from, and inception of, allergic airway disease. Severe lower respiratory tract viral infections are associated with recurrent wheeze, asthma and atopy. It is unclear if this association is causal and the underlying mechanisms governing this are unknown. Whilst respiratory viral infections are the major precipitants of acute exacerbations of wheezing illness, early life infections are also clearly associated with protection from allergic diseases. This article aims to review the current understanding of the complex relationship between lower respiratory tract viral infections and their impact upon development of atopy in the airway.
  
  
  RESULTS
  Clinical studies and animal models have further demonstrated that lower respiratory tract viral infections are strongly associated with development of recurrent wheeze and asthma with human rhinoviruses being shown to be the most prevalent cause of lower respiratory tract viral infections in infants, along with associated asthma development. A case-control study provided evidence of a contributory role for respiratory viral infections within this association, whilst recent experimental studies provide a possible mechanistic insight.
  
  
  CONCLUSIONS
  Progress into understanding the relationship between respiratory viral infections and allergic airway disease is essential for development of treatments aimed at treating common risk factors mediating association but not cause. Recent findings may have begun to identify key pathways open to therapeutic intervention.
authors.affiliation: Department of Respiratory Medicine, National Heart and Lung Institute, Imperial College London, London, UK.
authors.forename: Ross P
authors.initials: RP
authors.lastname: Walton
authors.forename: Sebastian L
authors.initials: SL
authors.lastname: Johnston
mesh_terms: D000818:Animals; D006168:Guinea Pigs; D006801:Humans; D007110:Immunity, Active; D051379:Mice; D023421:Models, Animal; D010850:Picornaviridae Infections / Q000150:complications* / Q000276:immunology; D012130:Respiratory Hypersensitivity / Q000209:etiology* / Q000276:immunology / Q000517:prevention & control; D018357:Respiratory Syncytial Virus Infections / Q000150:complications* / Q000276:immunology; D012136:Respiratory Syncytial Viruses; D012141:Respiratory Tract Infections / Q000150:complications* / Q000276:immunology; D012229:Rhinovirus; D018417:Th1 Cells / Q000166:cytology / Q000276:immunology; D018418:Th2 Cells / Q000166:cytology / Q000276:immunology