The proline-selective serine protease fibroblast activation protein (FAP) is a type II transmembrane glycoprotein. It is related to the dipeptidyl peptidases (DPPs) DPP2, DPP4, DPP8 and DPP9 and furthermore related to the endopeptidase prolyl oligopeptidase (PREP). FAP combines DPP and endopeptidase activities. FAP is not detectable in most healthy...