Reduced platelet production and impaired MK distribution and maturation. Scatter dot plots show the total number of MKs per low-power field (A) and the number of MKs adjacent to the vasculature in each low-power field (B) in the ITP group (n = 30) and control group (n = 28). (C) Representative graph of BM stained with anti-CD31 (red), anti-CD41 (green), and DAPI (blue) showing the distribution of vascular cells and MKs in the BM niche in the control group (scale bar, 100 μm). (D) Representative graph of BM stained with anti-CD31 (red), anti-CD41 (green), and DAPI (blue) showing the distribution of vascular cells and MKs in the BM niche in the ITP group (scale bar, 100 μm). Arrowheads in panels C-D indicate MKs near the sinusoids in the BM. Arrows in panels C-D indicate the endothelial cells in the BM. (E-E″) Representative graph of MKs in the vascular niche of the control group showing the size of MKs (scale bar, 20 μm). (F-F″) High-power magnification of MKs in the vascular niche of the control group showing the size of MKs (scale bar, 10 μm). (G-G″) Representative graph of MKs in the vascular niche of the ITP group showing the size of MKs (scale bar, 20 μm). (H-H″) High-power magnification of MKs in the vascular niche of the ITP group showing the size of MKs (scale bar, 10 μm). The white arrows in panels F″ and H″ refer to the sinusoids. (I) Scatter dot plots show the diameters of MKs located adjacent to the sinusoidal endothelium in the ITP group (n = 30) and the control group (n = 28). Data shown in panels A-B are pooled from 10 independent experiments with 4 to 8 samples per experiment. Data are shown as mean ± SD. Each point represents the mean adjusted value of 3 replicates for each individual patient. P values were calculated using the Mann-Whitney U test (A,I) or the Kolmogorov-Smirnov test (B). *P < .001, **P = .003.