The effect of tissue type-plasminogen activator deletion and associated fibrin (ogen) deposition on macrophage localization in peritoneal inflammation

There are two plasminogen activators (PAS), urokinase type-PA (u-PA) and tissue type-PA (t-PA). While u-PA is considered to be involved in cellular migration and tissue remodeling and t-PA in fibrinolysis, this distinction is not always clear-cut. With the use of u-PA and t-PA gene deficient mice (u-PA-/- and t-PA-/- mice, respectively) we have assessed the role of each PA in acute peritonitis. The cellular infiltrate in both thioglycolate- and antigen-induced peritoneal exudates was unaffected in u-PA-/- mice; in contrast, in t-PA-/- mice, the macrophage numbers, particularly of the Mac-I-hi population, in the peritoneal cavity by day 4 were significantly reduced compared to wild-type mice. However, examination of the peritoneal wall revealed in fact increased numbers of macrophages adhering on/in the cavity lining at all time points studied; in addition, increased fibrin(ogen) staining was observed for these mice. The reduced macrophage numbers in the peritoneal cavities of t-PA-/- mice could be increased by administration of plasmin or t-PA prior to harvesting the thioglycolate-elicited exudates. These results suggest that t-PA and not u-PA is the PA controlling fibrinolysis in murine peritonitis. In its absence macrophages adhere to the accumulated fibrinogen) on/in the cavity wall lining, most likely via Mac-I binding, thus affecting migration into and/or out of the peritoneal cavity. They also highlight the need to examine both the peritoneal cavity and wall in order to monitor accurately the extent of a peritoneal inflammatory reaction. Peritoneal inflammation in t-PA-/- mice represents a useful model to study the progression of intra-abdominal adhesions during surgery and clinical peritonitis.