Asthma is a common disease of the airways that involves episodes of bronchoconstriction with chronic infl ammation and eventual structural remodelling of the airways. Asthmatic airway infl ammation is characterized by the infi ltration of eosinophils, neutrophils, mast cells and activated T helper 2 (Th2) lymphocytes, which together with structural cells such as airway epithelial cells, smooth muscle cells, endothelial cells and fi broblasts, release a variety of infl ammatory mediators that are responsible for many of the pathophysiological processes occurring in the airways, including bronchoconstriction, mucosal and submucosal oedema, increased secretion of mucus and remodelling of the airways (Hamid and Tulic 2009).