Functional Domains in Thrombin Outside the Catalytic Site

Thrombin is known to be sequestered within the matrix of the fibrin gel, where it may remain active and intact for extended periods of time (Wilner et al., 1981; Mann, 1987). Since deposition of fibrin accompanies wound healing, thrombin may participate in modulation of this process. Inflammation is a localized protective response elicited by injury or destruction of tissues, which serves to destroy both the injurious agent and the injured tissue. Most forms of acute and chronic inflammation are amplified and propagated as a result of the recruitment of humoral and cellular components of the immune system. Immunologically mediated elimination of foreign material proceeds through a series of integrated steps. The actual destruction of antigens by immune mechanisms is mediated by cells with phagocytic capability. Such cells may migrate freely or may exist at fixed sites as components of the mononuclear phagocyte system. Since inflammation in its early stages is characterized by an influx of inflammatory cells, we wondered whether thrombin might participate in recruitment of such cells.