Requirement for cell-bound proteases in the mechanism of human neutrophil activation with various stimuli

A cell membrane-associated protease/esterase has been implicated in the mechanism of "stimulus-secretion coupling" described for human neutrophil degranulation. In this regard, a broad spectrum of protease inhibitors were evaluated for their effects on granule enzyme release from neutrophils exposed to soluble, surface-active stimuli. The serine protease inhibitors, L-1-tosylamide-2-phenylethyl-chloromethyl ketone (TPCK) and N-alpha-p-tosyl-L-lysine-chloromethyl ketone (TLCK) and a thiol protease inhibitor, p-hydroxymercuribenzoate (PHMB), caused a concentration-related suppression of neutrophil degranulation elicited with 1-O-hexadecyl/octadecyl-2-O-acetyl-sn-glyceryl-3-phosphorylcholine (AGEPC), ionophore A23187, phorbol myristate acetate (PMA), and 5(S), 12(R)-dihydroxy-6,14-cis-8,10-trans-eicosatetraenoic acid (LTB4). However, other inhibitors, such as aprotinin and p-hydroxyphenylpyruvic acid, were inactive. The maximum inhibitory effect with TPCK, TLCK, and PHMB was observed when neutrophils were exposed to these inhibitors prior to contact with the respective stimuli. In addition, the magnitude of inhibition increased in proportion to the preincubation time of protease inhibitor with stimulus. The results of these studies implicate proteases in the sequence of events underlying activation of the human neutrophil secretory process in response to structurally and chemically dissimilar stimuli.