PDE4A and airway hyperresponsiveness: Rolipram has been shown to reverse endotoxin-induced airway hyperresponsiveness and bronchoconstriction in vivo [30], whilst PDE4 knockdown attenuates basic fibroblast factor and interleukin-1β-induced proliferation, and transforming growth factor-β-induced myofibroblastic differentiation of fibroblasts [31].