Pulmonary fibrosis is a respiratory disease in which scars are formed in the lung tissues, leading to serious breathing problems. It is an immunological process that is known to be regulated by the immune modulator Peroxisome proliferator-activated receptors γ (PPARγ) and transforming growth factor β (TGF-β). PPARγ ligands antagonize the profibrotic effects of TGF-β in which induce differentiation of fibroblasts to myofibroblasts, a critical effector cell in fibrosis. These sequential set of events are described in this Adverse Outcome Pathway (AOP). The molecular initiating event (MIE) is inactivation of PPARγ which leads to TGF-β inactivation, a key event (KE) at molecular level. Next, key event at cellular level is differentiation of Myofibroblast and expression of collagen gene by activated TGF-β signaling pathway. Differentiated myofibroblast subsequently produce α-smooth muscle actin (α-SMA) and overexpressed collagen deposits in lung tissue. This consecutive KE resulting in the acquisition of the accumulation of excess fibrous connective tissue, the adverse outcome on pulmonary fibrosis. Scar formation, the accumulation of excess fibrous connective tissue (the process called fibrosis), leads to thickening of the walls, and causes reduced oxygen supply in the blood. As a consequence patients suffer from perpetual shortness of breath.