Immunohistochemistry of NF-E2 in HCs, RT, ET, PV, and PMF patients. (A-B represent HCs; D represents essential thrombocythemia; E represents PMF) Bone marrow biopsies were stained with an antibody against NF-E2 and counterstained with hematoxylin (original magnification ×1000; the bar indicates 20 µm). Arrows point to erythropoietic cells with nuclear NF-E2 staining, filled arrow heads indicate cytoplasmic NF-E2 staining, and open arrowheads mark cells negative for NF-E2 staining. (C,F-H) One hundred erythropoietic cells in each of 3 high-power fields per bone marrow biopsy (300 erythroid cells total) were evaluated for NF-E2 subcellular localization and/or differentiation stage. (C) Quantitative analysis of NF-E2 subcellular localization in HCs. Shown is the percentage of nuclear or cytoplasmic NF-E2–positive erythroid cells, respectively, and NF-E2–negative cells as a proportion of all erythroid precursors. (F) Quantitative analysis of nuclear NF-E2 positivity in erythroid cells in HC RT, and MPN patients. Shown is the percentage of nuclear NF-E2–positive erythroid cells as a proportion of all erythroid precursors. ****P < .0001 by 2-tailed Wilcoxon test. (G) Proportion of early and late erythroblasts of all erythroid cells in ET and PMF patients. Shown is the percentage of early and late erythroblasts as a proportion of all erythroid cells in ET and PMF patients. An early erythroblast was defined on a CAE stain as a CAE-negative erythroid cell with a small cytoplasm, a large nucleus (1.5-2.5–fold of the diameter of an erythrocyte), and 1 or 2 prominent nucleoli. A late erythroblast was defined as a CAE-negative cell, with abundant cytoplasm, frequently polygonal in shape, and with a round nucleus with dense chromatin. (H) Proportion of NF-E2 nuclear or cytoplasmic positive early erythroblasts in ET and PMF patients. Shown is the percentage of nuclear or cytoplasmic NF-E2–positive cells, as indicated, in early erythroid precursors. ***P < .001 by 2-tailed Wilcoxon test.