Analysis of platelet surface Mpl expression by flow cytometry. Washed platelets were incubated with anti-human Mpl rabbit IgG or normal rabbit IgG as isotype control. Binding was detected by labeling with FITC-conjugated anti-rabbit F(ab′)₂ fragment and fluorescence-activated cell sorter (FACS) analysis of CD41-gated cells. Gray-shaded histograms represent staining with the isotype control whereas solid black lines indicate staining with the Mpl antibody. Shown are the results obtained in healthy subjects (A,D) and patients with FPD/AML, who reveal reduced (B) or barely detectable (C,E,F) Mpl surface expression. Samples were analyzed in duplicate with similar findings.