IL13 and airway hyperresponsiveness: In fact, IL-4 is the key inducer of CD4+ Th cell commitment towards a Th2 immunophenotype, whilst IL-13 primarily promotes the development of bronchial inflammation and remodeling, thus enhancing airway hyperresponsiveness (Coyle et al., 1995; Grünig et al., 1998; Wills-Karp et al., 1998).