What have mast cells to do with edema formation, the consecutive repair and fibrinolysis?

Mast cells (MC) have been implicated in the activation of vascular endothelial cells, capillary leak formation, transmigration of white blood cells, and translocation of fibrinogen (and other plasma molecules) into the tissues, with consecutive edema formation. However, the mechanisms of repair that lead to tissue reconstitution after MC activation and edema formation have not been defined so far. In the present article, the possible contribution of MC to repair, in particular fibrinolysis, is discussed. Thus, accumulating evidence exists that human MC express and release the tissue-type plasminogen activator (tPA) in a constitutive manner. MC also express the urokinase receptor (uPAR) and heparin. Most importantly, however, MC lack plasminogen activator inhibitors (PAI-1, PAI-2, PAI-3). In line with this 'pro-fibrinolytic' profile of antigens, MC supernatants induce plasminogen-to-plasmin conversion and fibrin clot lysis in vitro. The c-kit ligand SCF upregulates uPAR expression, and the release of tPA from MC. These observations point to an important role of MC in endogenous fibrinolysis, a hitherto unrecognized (repair) function of this cell.