GPIbα^−/−platelets do not have increased c-Mpl density or enhanced TPO clearance function. (A) Representative immunoblots (left panel) and densitometry (right panel) of TPO receptor (c-Mpl) expression relative to glyceraldehyde-3-phosphate dehydrogenase (loading control) in GPIbα^−/− and WT BALB/c platelets (n = 6). ELISA-determined TPO levels from platelet lysates (internalized TPO) of GPIbα^−/− and WT BALB/c mice (B) and cultured supernatant supplemented with recombinant TPO following a 1-hour incubation of GPIbα^−/− or WT platelets (C) (n = 6). **P < .01, ****P < .0001. NS, not significant.