Thrombin‐induced chemotaxis and aggregation of neutrophils

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Abstract
Thrombin-induced neutrophil chemotaxis and aggregation were studied using cells isolated from either human or sheep blood. Sheep neutrophils (108 cells/ml) exhibited maximum chemotactic migration towards 10−8 M human α -thrombin, 10−8 M γ-thrombin (which lacks the fibrinogen site), and 10−12 MD-Phe-Pro-Arg-CH2-α-thrombin (catalytically inactive thrombin). Chemotactic responses of the same magnitude were obtained with human neutrophils (108 cells/ml). The chemotactic responses to thrombin were comparable to those obtained with diluted (1:200 v/v) zymosan activated serum (ZAS) and 10−11 M 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 to D-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 aggregation is an active site independent response.