CD71 is Selectively and Ubiquitously Expressed at High Levels in Erythroid Precursors of All Maturation Stages

Histology assessment of erythroid precursors in bone marrow biopsies can be challenging under pathologic conditions and often requires ancillary studies. CD71 (transferring receptor-1) is known to be expressed in the earliest erythroid precursors, and has been useful for flow cytometry. However, CD71 is also regarded as a proliferation marker, and its lineage specificity has not been systemically investigated by immunohistochemistry in detail. In this study, we found that CD71 was strongly expressed in all erythroid precursors in normal and dyspoietic marrows. Staining of CD71 effectively highlighted pronormoblasts in all 4 cases of parvovirus infection and erythroblasts in all 6 cases of acute erythroleukemia, for which staining of glycophorin A and hemoglobin A was either absent or unreliable. CD71 was absent in the background mature red blood cells in general, nonerythroid elements in the normal marrow, myeloid precursors in myeloproliferative disorders, and blasts in nearly all acute myeloid leukemia encompassing all common French-American-British subtypes. Benign lymphoid infiltrates and low-grade lymphomas involving the marrow also lacked detectable CD71. Although weak CD71 expression was found in acute lymphoblastic leukemia, diffuse large B-cell lymphoma, and 1 of 2 cases of acute megakaryoblastic leukemia, it had little impact on interpretation due to a high signal-to-noise ratio of the staining intensities when compared with erythroid precursors in the same section. We conclude that CD71 is selectively expressed at high levels in erythroid precursors, including those at early maturation stages. It can be reliably used as an independent erythroid marker for immunohistochemical analysis of the marrow.