AbstractThrombin‐induced neutrophil chemotaxis and aggregation were studied using cells isolated from either human or sheep blood. Sheep neutrophils (108cells/ml) exhibited maximum chemotactic migration towards 10−8M human α ‐thrombin, 10−8M γ‐thrombin (which lacks the fibrinogen site), and 10−12MD‐Phe‐Pro‐Arg‐CH2‐α‐thrombin (catalytically inactive thrombin). Chemotactic responses of the same magnitude were obtained with human neutrophils (108cells/ml). The chemotactic responses to thrombin were comparable to those obtained with diluted (1:200 v/v) zymosan activated serum (ZAS) and 10−11M FMLP. Premixing of the thrombin forms with hirudin in 1:1 stoichiometric amounts abolished the chemotaxis but not chemokinesis Aggregatory responses of human and sheep neutrophils were comparable for ZAS, α‐thrombin, and γ‐thrombin. The responses of both human and sheep neutrophils toD‐Phe‐Pro‐Arg‐CH2‐α‐thrombin were attenuated, indicating that the proteolytic site may be involved in the aggregatory response. The results suggest that thrombin‐induced neutrophil chemotaxis and aggregation are mediated by different mechanisms, since chemotaxis is a catalytically independent response whereas a
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