Detection of activated platelets using activation-dependent monoclonal antibody (SZ-51) in clinical disorders

Abstract

Platelets may become activated in a number of clinical disorders and participate in thrombus formation. A direct test for activated platelets in whole blood has been developed by radioimmunoassay with 125I labelled SZ-51, an antibody specific for an alpha-granule membrane protein (GMP-140) that associates with the platelet surface during secretion. The assay with sufficient sensitivity can be applied satisfactorily to detect as few as 2% activated platelets. In 50 normal subjects, minimal GMP-140 molecules per platelet were expressed on the surface of circulating platelets. The expression of GMP-140 molecules was increased transiently in 10 patients undergoing cardiopulmonary bypass, especially at the end of bypass. Evaluation of 18 patients with epidemic hemorrhagic fever (EHF) showed that the number of GMP-140 molecules on the platelet surface increased significantly, particularly at the shock phase, and closely related to the four different phases of EHF. In 9 patients suffered from acute myocardial infarction (AMI), the number of GMP-140 molecules changed with the procession of AMI and the highest occurred at the 48th h after AMI. The GMP-140 molecules were also increased in patients with asthma attack (n = 14), but not in patients with idiopathic thrombocytopenic purpura (n = 11). Considered together, these results suggest that activated platelets can be measured reliably in whole blood using radiolabeled SZ-51 antibody and the detection of activated platelets is potentially useful in identifying patients with certain thrombotic disorders.