Clearance of platelets in Mpl^-/- c-Myb^Plt4/Plt4 mice. Platelets were biotinylated in vivo, and then blood samples were collected at the times indicated. Platelets were identified flow cytometrically on the basis of size and CD41 positivity. (A) To measure platelet clearance, the number of labeled platelets at a given time (Bt) was divided by the initial number of labeled platelets (B, at 24 hours after biotin injection), and the logarithm of this ratio was plotted against time. (B) To monitor platelet production, the number of new unlabeled platelets (the number of unlabeled platelets at a given time less the initial number of unlabeled platelets) was plotted against time. Each point represents data from 2 to 3 mice of each genotype. □ indicates Mpl^-/ c-Myb^Plt4/Plt4; ○, Mpl^-/- c-Myb^+/+; and ▵, Mpl^+/+ c-Myb^+/+.