Respiratory syncytial virus and other respiratory viruses during the first 3 months of life promote a local TH2-like response

Background: Respiratory syncytial virus (RSV) infections during infancy are considered to be a risk factor for developing asthma and possibly allergic sensitization. Objective: The aim of this study was to investigate the cytokines, chemokines, and eosinophil cationic protein in the nasopharyngeal secretions of infants <= 7 months of age with RSV infections or other respiratory viral infections and healthy infants as controls. Groups were also analyzed according to age, <= 3 months and > 3 months, and the levels were compared within and between groups. Results: Thirty-nine infants with RSV, 9 with influenza or parainfluenza virus infections and 50 controls with no history of infections, were enrolled in the study. The RSV-infected infants had significantly higher levels of IL-4; macrophage inflammatory protein 1 beta, a chemoattractant for T cells; and eosinophil cationic protein in nasopharyngeal secretions compared with the control group. The levels of the T(H)2 cytokine IL-4 were significantly higher in RSV-infected infants : 3 months of age compared with RSV-infected infants > 3 months of age. In infants <= 3 months of age, infections with influenza or parainfluenza virus caused T(H)2-like responses similar to those produced by RSV. Conclusion: Infections with RSV as well as with influenza and parainfluenza virus during early infancy preferentially promote a T(H)2-like response in the nose with local production of IL-4, IL-5, and macrophage inflammatory protein 1 beta and infiltration and activation of eosinophils.