PDE4B encodes phosphodiesterase 4B, an enzyme that hydrolyzes the second messenger cAMP, playing a crucial role in regulating various physiological processes 1. The primary function involves degrading cAMP to terminate cAMP-mediated signaling pathways, thereby controlling inflammatory and fibrotic responses 2. PDE4B shows preferential expression in lungs and is distinct from other PDE4 isoforms in its cellular effects - unlike PDE4D, PDE4B overexpression exhibits protective effects against oxidative stress and hypertrophy in cardiomyocytes without affecting CREB-SIRT1 pathways 3. The enzyme is significantly involved in inflammatory diseases, with PDE4B-expressing macrophages infiltrating colonic mucosae in pediatric inflammatory bowel disease 4. Therapeutically, PDE4B represents a promising target for treating pulmonary fibrosis and other fibro-inflammatory conditions. Selective PDE4B inhibitors like nerandomilast (BI 1015550) demonstrate antifibrotic effects by inhibiting myofibroblast transformation, reducing extracellular matrix protein expression, and improving lung function parameters in preclinical models 15. These inhibitors show improved tolerability compared to pan-PDE4 inhibitors while maintaining anti-inflammatory and antifibrotic efficacy 6. Genome-wide association studies have also implicated PDE4B in neuropsychiatric conditions, including suicide attempt risk 7.