The PDE4 family includes PDE4A, PDE4B, PDE4C and PDE4D, all of which catalyze the hydrolysis of Camp.[490, 491] PDE4B is ubiquitously distributed in the brain, lung, immunocytes, heart and skeletal muscle and is an important therapeutic target of pulmonary fibrosis.[490, 492] Preferential inhibition of PDE4B has the potential to suppress inflammation and pulmonary fibrosis.[493] Inhibition of PDE4B may increase intracellular cAMP levels and suppress fibroblast proliferation, myofibroblast transdifferentiation, and ECM synthesis in the lung.[494]. Here, PDE4C is linked to pulmonary fibrosis.