Characterization of an antigen expressed on activated human T cells and platelets

We have identified a protein complex on the surface of activated human T cells and platelets. This Ag, detected by the murine mAb 1B3, is not expressed on resting human T cells or platelets or on other hematopoeitic cells. The majority of T cells express the Ag after stimulation with PHA, Con A, or allogeneic cells. Platelets express the Ag after activation with 1 U/ml thrombin. Immunoprecipitation of 125I-labeled activated T cells with antibody 1B3 shows a heterodimer of 180,000 and 155,000 Mr. An additional protein of 130,000 Mr is very faintly seen depending on the cell type. On platelets, the 180,000 Mr protein is the predominant protein immunoprecipitated under both nonreducing and reducing conditions. Antibody 1B3 may prove useful in identification of activated T cells and platelets as well as definition of specific mechanisms of T cell and platelet activation.