The response of the fibrinolytic system to mycobacteria infection.

The human pathogen Mycobacterium tuberculosis binds to a variety of host cell proteins, including those of the fibrinolytic system. These observations prompted us to study the expression of components of this system in an animal model of progressive pulmonary tuberculosis. Lung homogenates from BALB/c mice infected with M. tuberculosis H37Rv were analyzed to determine the expression and enzymatic activity of plasmin/plasminogen and tissue plasminogen activator, as well as the mRNA levels for plasminogen, tissue and urokinase plasminogen activators. Plasminogen was also detected in infected lungs with immunohistochemistry. The results show that the expression of molecules of the fibrinolytic system increased gradually over the course of the infection, peaking during the chronic phase of the disease. Furthermore, in vitro experiments showed that both plasminogen activators were specifically induced after the stimulation of spleen cells from BCG-immunized mice with M. tuberculosis proteins. Together, these results show that molecules of the fibrinolytic system are up-regulated in the chronic phase of experimental tuberculosis and suggest that the mycobacterium itself could play an important role in the overexpression of molecules of the fibrinolytic system, contributing to chronic inflammation in tuberculosis.

Antibodies to fibrin-bound tissue-type plasminogen activator in systemic lupus erythematosus are associated with Raynaud's phenomenon and thrombosis.

Fibrinolysis triggered by t-PA bound to fibrin is one of the main antithrombotic mechanisms. Defects in the fibrinolytic system-decreased tissue-type plasminogen activator (t-PA) activity and elevated levels of plasminogen activator inhibitor (PAI-1), in patients with SLE have been associated with an increased tendency to thrombosis. In the present study, 43 patients with SLE fulfilling the ACR criteria for the disease, were studied for the presence of autoantibodies to fibrin-bound t-PA, i.e. the physiological active form of this plasminogen activator. A solution of 200 IU/ml of t-PA was incubated with solid-phase fibrin prepared as previously described (Anal Biochem 1986; 153; 201-210). Sera diluted 1:50 were incubated with fibrin-bound t-PA, the plates were then washed, and bound immunoglobulins were detected using a polyvalent peroxidase-labeled goat anti-human Ig. Plates coated with fibrin alone were used as controls. Sera were considered positive when A490/630 obtained with normal human sera in two independent test was greater than the mean plus 2 SD. Eleven of 43 (26%) SLE sera demonstrated antibody reactivity against fibrin-bound t-PA. Within the anti-t-PA positive group there was a higher proportion of SLE patients with severe Raynaud's phenomenon and thrombotic events when compared to the anti-t-PA negative group: 36% vs 6% and 18% vs 6% respectively. These results suggest that autoantibodies to fibrin-bound t-PA could play a role in the pathogenesis of vascular disease in some SLE patients.

Regulacion de la fibrinolisis en la superficie celular / Regulation of fibrinolysis in the cell surface

El plasminogeno de la enzima fibrinolitica (Pm), es una glicoproteina de cadena sencilla. La conversion de Pg en la enzima activa sobre la superficie celular esta regulada por una serie de mecanismos complejos para lo cual es necesario la union de los componentes fibrinoliticos sobre los sitios de union especificos en la superficie de la celula. Existen 2 isoenzimas del Pg en el plasma denominadas Pg1 y Pg2. Ambas poseen identica estructura primaria pero difieren en sus propiedades fisicoquimicas. estudios recientes han demostrado que el Pg2 se une con mayor afinidad al receptor que el Pg1 que contiene mayor cantidad de carbohidratos, lo que demuestra el papel importante que desempenan las cadenas de carbohidratos del Pg para su union a la superficie celular