It is now widely accepted that apoptosis plays an important role in the selection of immature thymocytes and Ag-primed peripheral T cells. Fas (also known as CD95/APO-1) is a cell surface protein belonging to the tumor necrosis factor receptor superfamily, which is expressed in a variety of normal and neoplastic cells. Binding of FasL to Fas or crosslinking of Fas by anti-Fas monoclonal antibodies results in rapid induction of apoptosis in Fas expressing cells. Clone ZB4 is known as Fas blocking, Fas neutralizing or Fas antagonistic antibody, whereas anti-human Fas antibody (clone CH-11) is known as the agonistic antibody.Synonyms: APT1, Apo-1 antigen, FAS1, FASLG receptor, TNFRSF6, Tumor necrosis factor receptor superfamily member 6