Immunohistochemical staining of paraffin sections of a bone marrow biopsy from a patient with PV.

Serial sections were stained with a polyclonal antibody to native PRV-1 (panel A), to naphthol-AS-D-chloroacetate esterase (NACE, panel B), or with an antibody to hemoglobin (panel C). In panel A, the large arrowhead points to an early erythroblast, the small arrowhead points out a megakaryocyte, and the open arrow shows a promyelocyte. A 1:400 magnification is shown.