This follow up study was performed on patients with myocardial infarction (MI) in order to test their immunocompetance before and after treatment with actilyse, a fibrinolytic drug used to dissociate thrombosis plaque. Fifteen patients with an acute myocardial infarction were given a 100 mg actilyse over 90 minutes. Blood : samples were collected before treatment and at different time intervals following treatment to perform the following tests: - Lymphocyte transformation assay. Phagocytic activity. Plasma immunosuppressive activity to blastogenesis. The role of alpha-2-macroglobulin, its level and protease binding properties. Human alpha-2-macroglobulin (a2M) was purified from plasma by gel filteration chromatography. The purified alpha-2-macroglobulin (a2M) was used to produce anti-a2M for determination of alpha-2-macroglobulin concentration in patient's plasma by rocket immunoelectrophoresis. The trypsin binding activity of alpha-2-macroglobulin was determined by measuring the esterolytic activity of Trypsin-alpha-2-