Indeed, the administration of 3 mg/kg pan PDE4 inhibitor rolipram could further decrease neutrophil infiltration in the lungs of lipopolysaccharide (LPS)-induced chronic obstructive pulmonary disease (COPD) in PDE4B knock-out (KO) mice and, to a lesser extent, in PDE4D KO mice, suggesting a promising role of PDE4D in orchestrating neutrophil infiltration [53]. Here, PDE4D is linked to chronic obstructive pulmonary disease.