Disruption of GPIbα-flnA interaction induces macrothrombocytopenia with reduced GPIb expression. (A) Anticoagulated whole blood from hGPIbα^WT and hGPIbα^FW mice was assessed for platelet GPIb surface expression by flow cytometry using anti–CD42b-PE Ab. The results are expressed as the mean fluorescence intensity of the gated platelet population (mean ± SEM of n = 20 pairs of hGPIbα^WT and hGPIbα^FW mice; ∗∗∗∗P < .0001, unpaired t test.). (B) Representative histograms of GPIbα expression (CD42b-PE) in hGPIbα^WT (red), hGPIbα^FW (blue), and mNull (broken black line) platelets in whole blood. (C) EDTA-anticoagulated whole mouse blood was assessed using a Sysmex blood analyzer for mean platelet volume. Graph demonstrates mean ± SEM of 10 mice from each strain. (D) Representative DIC images of fixed platelets adherent to VWF/botrocetin matrix (scale bar, 3 μm). (E) Platelet count in EDTA-anticoagulated whole blood from hGPIbα^WT and hGPIbα^FW mice was determined using a Sysmex blood analyzer. Results represent the mean ± SEM of hGPIbα^WT and hGPIbα^FW mice (n = 20 of each strain), ∗∗∗∗P < .0001, unpaired t test. (F) In vivo platelet life span was determined for hGPIbα^WT and hGPIbα^FW mice using in vivo biotinylation. Results depict the mean ± SEM of hGPIbα^WT and hGPIbα^FW mice (n = 4 and n = 5, respectively), P = .8162 for strain comparisons, 2-way ANOVA. Ab, antibody; ANOVA, analysis of variance; SEM, standard error of the mean.