Preparation of a monoclonal antibody, SZ-51, that recognizes an alpha-granule membrane protein (GMP-140) on the surface of activated human platelets.

To identify the changes on the platelet plasma membrane after platelet activation, we prepared monoclonal antibodies specific for activated platelets. Hybridoma cell line SZ-51 was screened for antibodies which bound to thrombin activated platelets but not to resting platelets. 125I-SZ-51, and IgG1, bound 780 molecules/platelet on resting platelets. However, it bound 11,000 molecules/platelet on thrombin activated platelets with high affinity (4.2 nmol/L). The isolated protein using affinity chromatography showed a single band in both periodic acid-Schiff and Coomassie blue staining. Immunoblot analysis revealed that SZ-51 reacted with a 140,000 molecular weight protein which was identified to be alpha-granule membrane protein (GMP-140) in radioimmunoassay. These results demonstrate that the antigen recognized by SZ-51 is GMP-140, which is expressed on the plasma membrane of activated platelets.