Fas Ligand is a 40 kDa type II transmembrane protein belonging to the TNF superfamily. The specific receptor for Fas Ligand is Fas (CD95, Apo-1). Fas Ligand is predominantly expressed on activated T cells and natural killer cells, while Fas is expressed on various types of cells. The Fas/Fas Ligand system plays a crucial role in modulating immune responses by inducing cell specific apoptosis. Human Fas Ligand shares 81% sequence identity with mouse Fas Ligand and 78% sequence identity with rat Fas Ligand.