TLT-1 expression is greater than P-selectin expression on the surface of activated megakaryocytes and platelets in vitro. (A) Whole-cell lysates of primary BM-derived mouse megakaryocytes 0 to 5 days after thrombopoietin (Tpo) administration were western blotted for TLT-1, P-selectin, and ERK1/2. Representative blots of 2 independent experiments. (B) BM-derived megakaryocyte surface expression of TLT-1 and P-selectin following collagen stimulation (30 µg/mL) for 20 minutes at 37°C. Data are presented as mean fluorescence intensity (MFI) ± SD; n = 7-9. (C-D) Platelet surface expression of TLT-1 and P-selectin was measured by flow cytometry in response to the protease activated receptor agonist thrombin and the glycoprotein VI–specific agonist CRP in murine (C) and human (D) whole blood. (i) Dose-response (thrombin, 0.03-3 U/mL; CRP, 3-30 µg/mL) and (ii) time course (thrombin, 0.1 U/mL; CRP, 10 µg/mL). Data are presented as median fluorescence intensity ± SD; n = 3-6 independent experiments per condition. *P < .05, **P < .01, ***P < .001 vs basal.