Vitronectin

The multifaceted complement regulator vitronectin (Vn) can be found in almost all tissues of the human body. It is primarily produced by the liver and is thus detected at high concentrations in plasma. Upon inflammation, Vn is upregulated revealing its importance for the innate immune defence against danger signals. It consists of 459 amino acids and has several key sequences linked to its functions. Vn interacts at its N-terminal with plasminogen activator inhibitor-1 and urokinase-type plasminogen activator receptor (uPAR). Downstream of these binding sites are sequences that attract integrins and collagen in addition to the thrombin-antithrombin III complex. Heme-binding plasma proteins, as well as plasminogen, can also interact with Vn through heparin-binding domains. One of the main functions of Vn is to inhibit the terminal pathway of the complement system by preventing formation of the lethal pore-forming complex. This chapter will in detail discuss the knowledge on this important molecule.