Thrombus imaging in dogs with a monoclonal antibody (SZ-51) specific for activated human platelets.

To specifically detect the localization of thrombus in vivo, we prepared a monoclonal antibody (McAb) SZ-51 specific for an alpha-granule membrane protein (GMP-140) on the surface of activated human platelets. The thrombus binding rate in vitro was 80 +/- 5% for 131I-SZ-51 and 4.4 +/- 0.5% for 131I-nonimmune IgG. Owing to the crossreaction of McAb SZ-51 with the activated platelets of dogs, thrombus in the femoral artery and vein of dogs was formed and imaged with single photon emission computerized tomography (SPECT). The ratio of thrombus to blood radioactivity (T/B) was 2.1, 4.8, 14.0 and 18.0 at 1, 2, 3 and 4 hours after injection of 131I-SZ-51 (0.6 mCi, 50 micrograms) into the arterial thrombus respectively, while the T/B ratio was 1.7, 2.2, 5.3 and 8.0 for venous one. The injection of 131I-nonimmune IgG at the same doses yielded a T/B ratio of 1.2 +/- 0.3 at each time period for both arterial and venous thrombi. These findings were in good agreement with the counting of removed thrombi 24 hours after the injection of radiotracer. The ratio was 21.7 and 2.6 for the 131I-SZ-51 in the arterial and venous thrombus, respectively. However, there were only 1.48 and 1.6 for the 131I-nonimmune IgG. These results indicate the great potentiality of McAb SZ-51 in application to detection of thrombi in vivo.