Vitronectin (Vn) is an important human glycoprotein involved in maintaining homeostasis via regulation of the fibrinolytic system. Vn also functions as a complement regulator by inhibiting the terminal complement pathway during C5b6-7 complex formation and C9 polymerization. Several bacterial pathogens have been shown to recruit Vn to the cell surface as a means of resisting complement deposition. In addition, Vn functions as a "sandwich" molecule between bacteria and host epithelial cell receptors, thereby promoting adherence and internalization of pathogens. Binding of Vn to the bacterial cell surface is mediated by other currently unidentified proteins.