CD95, also known as Fas and APO-1, is a 45 kDa type I transmembrane glycoprotein and a member of the tumor necrosis factor receptor superfamily. It is expressed by activated lymphocytes, monocytes, neutrophils, fibroblasts, and cell lines. Fas ligand binding to CD95 induces apoptosis in activated mature lymphocytes thereby playing a role in maintaining peripheral tolerance.