DPP4 and idiopathic pulmonary fibrosis: DPP4 also possess non-enzymatic functions including its role as a T-cell co-stimulatory protein and interactions with extracellular matrix proteins such as collagen and fibronectin, which are increased in IPF (Löter et al., 1995; Gorrell et al., 2001; Cheng et al., 2003).