It is now widely accepted that apoptosis plays an important role in the selection of immature thymocytes and Ag-primed peripheral T cells. Fas antigen is a cell-surface protein that mediates apoptosis. It is expressed in various tissues including the thymus and has structural homology with a number of cell-surface receptors, including tumor necrosis factor receptor and nerve growth factor receptor.Synonyms: APT1, Apo-1 antigen, FAS1, FASLG receptor, TNFRSF6, Tumor necrosis factor receptor superfamily member 6