Apoptosis can be induced by certain cytokines including TNF and Fas Ligand of the TNF super-family throμgh their death domain (DD) containing receptors, TNFR1 and Fas. A member of the TNF receptor family was recently identified and designated DR4 (death receptor 4) and TRAIL-R1. The ligand for this novel death receptor has been identified and termed TRAIL. DR4 is expressed in most of the human tissues including spleen, peripheral blood leukocytes (PBLs), small intestine and thymus. Like TNFR1, Fas and DR3, DR4 mediates apoptosis and NFkB activation in many tissues and cells.