The tumor necrosis factor (TNF) superfamily is a protein superfamily of transmembrane proteins containing TNF homology domain and forming trimers. Members of this superfamily can be released from the cell membrane by extracellular proteolytic cleavageand function as a cytokine. These proteins are expressed predominantly by immune cells and regulate diverse cell functions, including regulation of immune response and inflammation, but also proliferation, differentation, apoptosis and embryogenesis. The superfamily contains 19 members that bind to 29 members of TNF receptor superfamily.