Expression of fibrinolytic antigens in redistributed cardiac mast cells in auricular thrombosis

Recent data suggest that auricular thrombosis is associated with an increase and accumulation of mast cells (MC) in the subendothelial region of the upper endocardium. However, the molecular basis and the functional role of MC in this process are not known. In the current study, expression of fibrinolytic and antifibrinolytic antigens in human cardiac MC was analyzed by immunohistochemistry. MC were found to react with antibodies against tissue-type plasminogen activator (tPA) and urokinase receptor (uPAR/CD87), but not with antibodies against urokinase (uPA) or plasminogen activator inhibitors (PAI-1, PAI-2). Significant changes were observed when the phenotype of accumulated MC in the upper endocardium in patients with auricular thrombosis was compared with the phenotype of myocardial MC in the same patients or with MC in normal hearts. These redistributed MC stained less intensely with antibodies against tPA and chymase but retained their staining for tryptase and uPAR. Together, these data indicate that cardiac MC are a source of fibrinolytic antigens and that accumulation of MC in auricular thrombosis is associated with phenotypic changes of MC and loss of cellular tPA. It is hypothesized that MC and their products may play a role in endogenous fibrinolysis in auricular thrombosis.