Previous studies have shown that efficient virus clearance requires Th1-type responses characterized by IFN-γ, IL-2 and IL-12 expression, and that a bias toward Th2-type responses can contribute to RSV pulmonary disease characterized by airway hyperresponsiveness, mucus over-production, wheezing, bronchiolitis, and pulmonary eosinophilia [33,35,73–75]. Here, IL2 is linked to bronchiolitis.