The specific binding of thrombin to human polymorphonuclear leucocytes.

Thrombin is a chemotaxin for polymorphonuclear leucocytes. In this paper the binding kinetics of 125I-labelled thrombin to purified polymorphonuclear leucocytes is characterized. At 4 degrees C, the 125I-labelled thrombin bound to the cells with a half-time of about 3 min. About 0.77 of the bound tracer dissociated upon addition of a surplus of unlabelled thrombin or hirudin. Each cell possessed about 50 receptors with a Kd of 18 pmol/l and about 6000 receptors with a Kd of 31 nmol/l. Although the binding affinity at 37 degrees C was 7-10-fold lower than that measured at 4 degrees C, it may be high enough to constitute the molecular basis for the reported thrombin-induced chemotaxis.