The UK98/6 monoclonal antibody specifically recognizes Urokinase-type Plasminogen Activator (uPA) that is encoded by PLAU (Plasminogen Activator Urokinase). uPA (PLAU) is secreted as an inactive single-chain precursor protein (Pro-urokinase or Pro-uPA) by various cells including vascular endothelial cells, renal epithelial cells, fibroblasts, monocytes, macrophages, smooth muscle cells and tumor cells of different origin. Following proteolytic cleavage, two resulting chains are disulfide bonded together with an amino-terminal A-chain (ATF) with EGF-like growth factor and Kringle domains bound to a catalytically active peptidase, the C-terminal B-chain. uPA (PLAU) binds to cell-surface CD87 (also known as, Urokinase Plasminogen Activator Receptor or uPA-R) by its growth factor-like domain. CD87 is widely expressed by monocytes, neutrophils, dendritic cells, activated T cells, NK cells, fibroblasts, endothelial cells, keratinocytes, and some tumor cells. The cell-associated form of uPA (PLAU) efficiently acts upon the plasminogen proenzyme to generate active plasmin which degrades blood plasma proteins and dissolves fibrin blood clots. uPA (PLAU) also activates collagenases that are involved in the breakdown of the extracellular matrix as well as some mediators of the complement system. It may play a role in tumor cell proliferation, migration, and metastases. A specific polymorphism of uPA (PLAU) is associated with late-onset Alzheimer's disease. The UK98-6 antibody can reportedly suppress the biological activity of uPA (PLAU).