Cells undergo programmed cell death in response to various stimuli. Apoptosis is essential for morphogenesis, tissue homeostasis, and host defense (5). It is induced by certain cytokines including TNF and Fas ligand in the TNF family through their death domain containing receptors, TNFR1 and Fas. A death domain containing receptor was identified and designated DR4 (4). The ligand for this death receptor has been identified and termed TRAIL (2,3), which is a new member in the TNF family. DR4 is also called TRAIL receptor-1 (TRAILR1) (1). DR4 is expressed in most human tissues including spleen, peripheral blood leukocytes, small intestine and thymus. Like TNFR1, Fas and DR3, DR4 mediates apoptosis and NF-kB activation in many tissues and cells.
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