AJP - Cell Physiology, Vol 258, Issue 6 C1100-C1107, Copyright © 1990 by American Physiological Society
Activation of human platelets by C5a-stimulated neutrophils: a role for cathepsin G
P. Ferrer-Lopez, P. Renesto, M. Schattner, S. Bassot, P. Laurent and M. Chignard
Unite Associee IP-Institut National de la Sante et de la Recherche, Medicale 285, Institut Pasteur, France.
Human platelets can be stimulated by recombinant human fifth component of
complement (rhC5a) in the presence of human neutrophils. After challenge
with N-formyl-Met-Leu-Phe or rhC5a, concentrated neutrophils release
cathepsin G into the supernatant. The concentrations of cathepsin G
recovered by titration of the enzymatic activity correlate with the
capability of these supernatants to induce platelet stimulation as measured
by serotonin release. Cathepsin G purified from neutrophil granules
triggered platelet aggregation and serotonin release independent of
arachidonic acid metabolites and platelet-activating factor formation. A
concentration of 100 nM of cathepsin G, which was reached in the
surrounding space of activated neutrophils, induced a 50% platelet
stimulation. Three distinct antiproteinases were tested against cathepsin
G-induced platelet activation. Z-Gly-Leu-Phe-CH2Cl, a specific inhibitor of
cathepsin G enzymatic activity, proved to be nonspecific in our biological
system. By contrast, alpha 1-antichymotrypsin and alpha 1-antitrypsin
displayed specific activities. The physiological specific inhibitor of
cathepsin G, alpha 1-antichymotrypsin, was the most potent and was used in
the rhC5a-induced neutrophils-mediated platelet activation. A complete
inhibition was achieved, showing that release of cathepsin G from
neutrophils accounts for platelet activation. Such a chain of events
involving C5a, neutrophils, cathepsin G, and platelets may be of relevance
in certain inflammatory states, particularly the adult respiratory distress
syndrome.
