Immunohistochemistry of NF-E2 in MPN,U, ET, and PMF patients. Bone marrow biopsies were stained with an antibody against NF-E2 and counterstained with hematoxylin (original magnification ×1000, bar indicates 20 µm). Arrows point to erythropoietic cells with nuclear NF-E2 staining and filled arrowheads indicate cytoplasmic NF-E2 staining. (A) MPN,U later reclassified as ET. (B) MPN,U later reclassified as PMF. (C) ET later reclassified as PMF. (D) Quantitative analysis of NF-E2 immunohistochemistry in MPN,U patients. One hundred erythropoietic cells in each of 3 high-power fields per bone marrow biopsy were evaluated (300 erythroid cells in total). Shown is the percentage of nuclear NF-E2–positive erythroid cells as a proportion of all erythroid precursors. Data for ET and PMF are presented as in Figure 2F; **P < .01, ****P < .0001 by Wilcoxon test.