Color Atlas of Hematology - Practical Microscopic and Clinical ...

30Normal Cells of the Blood and Hematopoietic OrgansThe Individual Cells of HematopoiesisImmature Red Cell Precursors: Proerythroblasts andBasophilic ErythroblastsProerythroblasts are the earliest, least mature cells in the erythrocyteformingseries (erythropoiesis). Proerythroblasts are characterized bytheir size (about 20 µm), and by having a very dense nuclear structurewith a narrow layer of cytoplasm, homogeneous in appearance, with alighter zone at the center; they stain deep blue after Romanowsky staining.These attributes allow proerythroblasts to be distinguished frommyeloblasts (p. 35) and thus to be assigned to the erythrocyte series. Aftermitosis, their daughter cells display similar characteristics except thatthey have smaller nuclei. Daughter cells are called basophilic erythroblasts(formerly also called macroblasts). Their nuclei are smaller and the chromatinis more coarsely structured.The maturation of cells in the erythrocyte series is closely linked to theactivity of macrophages (transformed monocytes), which phagocytosenuclei expelled from normoblasts and iron from senescent erythrocytes,and pass these cell components on to developing erythrocytes.Diagnostic Implications. Proerythrocytes exist in circulating blood onlyunder pathological conditions (extramedullary hematopoiesis; breakdownof the blood–bone marrow barrier by tumor metastases, p. 150; orerythroleukemia, p. 100). In these situations, basophilic erythroblasts mayalso occur; only exceptionally in the course of a strong postanemia regenerationwill a very few of these be released into the blood stream (e.g.,in the compensation phase after severe hemorrhage or as a response tovitamin deficiency, see p. 152).