title: Early-life viral infection and allergen exposure interact to induce an asthmatic phenotype in mice.
abstract: BACKGROUND
  Early-life respiratory viral infections, notably with respiratory syncytial virus (RSV), increase the risk of subsequent development of childhood asthma. The purpose of this study was to assess whether early-life infection with a species-specific model of RSV and subsequent allergen exposure predisposed to the development of features of asthma.
  
  
  METHODS
  We employed a unique combination of animal models in which BALB/c mice were neonatally infected with pneumonia virus of mice (PVM, which replicates severe RSV disease in human infants) and following recovery, were intranasally sensitised with ovalbumin. Animals received low-level challenge with aerosolised antigen for 4 weeks to elicit changes of chronic asthma, followed by a single moderate-level challenge to induce an exacerbation of inflammation. We then assessed airway inflammation, epithelial changes characteristic of remodelling, airway hyperresponsiveness (AHR) and host immunological responses.
  
  
  RESULTS
  Allergic airway inflammation, including recruitment of eosinophils, was prominent only in animals that had recovered from neonatal infection with PVM and then been sensitised and chronically challenged with antigen. Furthermore, only these mice exhibited an augmented Th2-biased immune response, including elevated serum levels of anti-ovalbumin IgE and IgG1 as well as increased relative expression of Th2-associated cytokines IL-4, IL-5 and IL-13. By comparison, development of AHR and mucous cell change were associated with recovery from PVM infection, regardless of subsequent allergen challenge. Increased expression of IL-25, which could contribute to induction of a Th2 response, was demonstrable in the lung following PVM infection. Signalling via the IL-4 receptor alpha chain was crucial to the development of allergic inflammation, mucous cell change and AHR, because all of these were absent in receptor-deficient mice. In contrast, changes of remodelling were evident in mice that received chronic allergen challenge, regardless of neonatal PVM infection, and were not dependent on signalling via the IL-4 receptor.
  
  
  CONCLUSIONS
  In this mouse model, interaction between early-life viral infection and allergen sensitisation/challenge is essential for development of the characteristic features of childhood asthma, including allergic inflammation and a Th2-biased immune response.
authors.affiliation: Department of Pathology, University of New South Wales, Sydney, NSW, Australia.
authors.forename: Jessica S
authors.initials: JS
authors.lastname: Siegle
authors.forename: Nicole
authors.initials: N
authors.lastname: Hansbro
authors.forename: Cristan
authors.initials: C
authors.lastname: Herbert
authors.forename: Helene F
authors.initials: HF
authors.lastname: Rosenberg
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Domachowske
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Asquith
authors.forename: Paul S
authors.initials: PS
authors.lastname: Foster
authors.forename: Rakesh K
authors.initials: RK
authors.lastname: Kumar
mesh_terms: D000485:Allergens / Q000633:toxicity; D000818:Animals; D000831:Animals, Newborn; D001249:Asthma / Q000503:physiopathology* / Q000821:virology*; D051379:Mice; D008807:Mice, Inbred BALB C; D010641:Phenotype; D018357:Respiratory Syncytial Virus Infections / Q000503:physiopathology* / Q000821:virology*; D012136:Respiratory Syncytial Viruses / Q000502:physiology*
chemical_list: D000485:Allergens