Cationic proteins of human granulocytes Effects on human platelet aggregation and serotonin release.

Immune-aggregate and thrombin-mediated [(3)H]serotonin release from human platelets are shown to be enhanced when platelets are preincubated with the antibacterial chymotrypsin-like cationic protein isolated from human granulocytes. The enhancement is dose dependent and inhibited by heating of the cationic protein. Release with chymotrypsin-like cationic protein alone was not observed, although the protein was shown to "micro-aggregate" platelets irreversibly by an ADP-dependent reaction. Platelet "macro-aggregation" induced by immune-aggregate was also enhanced by chymotrypsin-like cationic protein whereas platelet "macro-aggregation" induced by thrombin was inhibited competitively. Platelet "micro-aggregation" induced by chymotrypsin-like cationic protein was inhibited when preincubated for more than 5 min with a 2-fold molar excess ofα-1-antitrypsin. Chymotrypsin-like cationic protein interaction with several platelet reactions suggests a close relationship between neutrophils and platelets in the inflammatory process.