Effects of platelet depletion on senescent RBC retention in the circulation. (A-D) Cohorts of mice were pulse-labeled with NHS-biotin (IV, day 0) and then treated with platelet-depleting anti-GPIbα or nonimmune isotype (control) antibodies on day 45, at which time the mean proportions of P-RBC complexes in the labeled RBCs were significantly higher than in the unlabeled RBCs (mean ± SEM: 7.6% ± 1.2% vs 1.36% ± 0.17%; P < .0001). Blood samples were taken at indicated intervals and analyzed for percentages of biotin-labeled and unlabeled P-RBC complexes (B), biotin-labeled RBCs (normalized to day 45 levels) (C), and the relative RBC clearance rates (D). Clearance rates (determined by nonlinear regression) are shown separately for the days 45 to 48 and days 48 to 52 periods (indicated by vertical dashed lines in panel C). Comparisons shown between treatment groups using ANOVA; 8 mice per group, 2 independent experiments. (E-G) Mpl^−/− and Mpl^+/+ mice were pulse-labeled with NHS-biotin and blood samples taken at indicated intervals and analyzed for percentages of biotin-labeled and unlabeled P-RBC complexes (F) and biotin-labeled RBCs (G). Comparisons shown between treatment groups using ANOVA; 5 mice per group. (H-J) Proportions of P-RBC complexes (H) and annexin V–stained (I) and anti-FasR–stained (J) RBCs in blood samples collected from 9 patients with primary ITP and 9 healthy controls. Comparisons shown between groups using Student t test. Bars indicate means.