Expression of c-mpl in essential thrombocythemia.

(A) All megakaryocytes show a uniform, strong staining intensity (× 320). The inset shows a higher magnification of a strongly stained megakaryocyte (× 1000). (B) Heterogeneous pattern of c-mplexpression with coexistence of strongly positive megakaryocytes and a significant percentage of megakaryocytes showing a moderate staining intensity (× 250). Some strongly stained plasma cells are also present. The inset shows a higher magnification of a moderately stained megakaryocyte (× 1000). (C) Heterogeneous pattern of c-mplstaining with moderately positive megakaryocytes together with several weakly stained megakaryocytes (× 250). Several plasma cells show strong c-mpl positivity. The inset shows a higher magnification of a cluster of weakly stained megakaryocytes (× 1000). (D) Heterogeneous pattern of c-mpl expression characterized by the presence of several c-mpl–negative megakaryocytes together with some moderately stained megakaryocytes and a few strongly stained plasma cells (× 250). The inset shows a higher magnification of a c-mpl–negative megakaryocyte (× 1000) (avidin-biotin-peroxidase–complex method in paraffin section lightly counterstained with hematoxylin).