The NOK-1 monoclonal antibody specifically reacts with human CD178, which is the CD95 or Fas ligand. CD178 is a TNF superfamily type II transmembrane glycoprotein expressed by activated T and NK cells and is involved in Fas-mediated apoptosis of lymphocytes. CD178 is also expressed by monocytes, neutrophils, granulocytes and the parenchymal cells of the retina and cornea. The NOK-1 antibody has been reported to bind to COOH-terminus of the Fas ligand in the region associated with Fas binding.