TPO (100 ng/mL) upregulates the activation state of α_IIbβ₃ (A) and the α_IIbβ₃-binding adhesion of ⁵¹Cr-labeled platelets to immobilized fibrinogen (B). FACScan analysis and binding experiments were performed as described in Materials and Methods. In (A), data are expressed as means ± SD of three to six separate experiments. In (B), data are expressed in cpm and represent means ± SD of three separate experiments.