| Popis: |
PADGEM protein is a platelet-specific alpha grannie membrane protein that is translocated to the plasma membrane during platelet activation and secretion. Monoclonal EC4 and polyclonal anti-PADGEM antibodies are specific for PADGEM on activated platelets. Because PADGEM is internal in unstimulated platelets* these antibodies do not bind to resting platelets. Since activated platelets are concentrated in thrombi, we used radiolabeled anti-PADGEM antibodies to image thrombi in baboons.In vitro: Dacron graft material incubated with thrombin-activated platelet-rich plasma and 131I-KC4, 131I-anti-PADGEM, 131I-nonimmune IgG or 131-BSA bound 95%, 70%, 9% and 1% of the radiolabel, respectively, after exhaustive washing.In vivo: Imaging experiments were carried out in baboons with an external Dacron shunt between the femoral artery and vein. Gamma camera images following 123I-anti-PADGEM infusion (1.0 mCi; 300 μg) demonstrated intense uptake in the thrombus induced by the Dacron vascular graft within 10 minutes. The graft:blood pool activity ratio was 33:1. Control experiments with 123I-nonimmune IgG showed minimal uptake. 123I-anti-PADGEM cleared the circulating blood pool with an initial half-disappearance time of 2-6 minutes. The primary routes of metabolism were hepatic uptake, dehalogenation and urinary excretion of free iodine. There was no evidence that the anti-PADGEM antibodies had any adverse effects on the normal processes of hemostasis in any of these experiments.Anti-PADGEM antibodies, both monoclonal and polyclonal, are directed against activated platelets in thrombi or in areas of tissue injury; they do not bind to resting platelets in the circulation. Radioimmunoscintigraphy with these agents provides a novel approach to the noninvasive detection and localization of thrombi in vivo, with potential application to human disease. Furthermore, linkage of these antibodies to fibrinolytic enzymes offers a strategy for the specific lysis of thrombi in vivo. |
