EVIDENCE FOR PROTEASES WITH SPECIFICITY OF CLEAVAGE AT AROMATIC AMINO ACIDS IN HUMAN NATURAL CELL-MEDIATED CYTOTOXICITY

Abstract

Publisher Summary This chapter examines the evidence for proteases with specificity of cleavage at aromatic amino acids in human natural cell-mediated cytotoxicity. In a study described in the chapter, lymphocyte-K562 conjugates were formed by centrifuging 2:1 mixtures of peripheral blood mononuclear cells and K562 cells for 3 minutes at 40g at room temperature. The inhibition of NK by plasma antiproteinases implies that a protease of the serine-dependent type is required for killing because these antiproteinases inactivate only this class of protease. The marked inhibitory activity of a-1-X to both slow and fast NK implies that at least one serine-dependent protease with chymotrypsin-like activity is crucial to NK. It is likely that the protease activity is either membrane-associated or released upon activation of the lytic mechanism because plasma antiproteinases are large acidically charged molecules which are unlikely to cross lymphocyte membranes. It was found that because pretreatment of lymphocytes with plasma antiproteases followed by washing has no subsequent effect, this indicates that the NK protease is either not activated and/or sequestered prior to killing. This conclusion that a protease with aromatic amino acid specificity is required for NK is further supported by the data from the experiments using ester and amide derivatives of aromatic amino acids to inhibit NK to K562 cells.