PDE4A and asthma: In the context of allergic airway inflammation and asthma, phosphodiesterase 3 (PDE3) and PDE4 are widely expressed in airway cells, including epithelial and endothelial cells, smooth muscle cells, and inflammatory cells (Beavo, 1995; Blease et al., 1998; Wright et al., 1998; Myou et al., 1999; Souness et al., 2000; Boswell-Smith et al., 2006).