CD105 expression in early erythroid precursors.

Abstract

We read with interest the article by Wang et al. regarding pure erythroid leukemia (PEL).1 In the immunophenotype and markers section for PEL they consider that ideally a marker for PEL should only highlight proerythroblasts and be negative in more mature erythroid cells and cells of other lineages. The CD105 antigen (endoglobin) has been traditionally used as an endothelial marker.2 Mesenchymals cells also express CD105 in combination with CD13, CD10, HLA-DR, and CD90 without reactivity for CD45 and CD117 markers.3 Using six to eight-colors flow cytometry in different antigens combinations, CD105 can also be used to detect immature erythroid progenitors. Human BFU-E are CD34+, CD45+, Glicophorin A (CD235a)–, CD36– or low, and CD71 low, whereas CFU-E cells are CD34–, CD235a–, CD36+, and CD71++.4 In Figure 1, a subset of CD34 cells (dark green cells) CD117+ shows a progressive expression of CD105 and CD36 and may be considered the CD34+ erythroid progenitors. Proerythroblasts are characterized by their expression of CD117+, CD105++, HLA-Dr–/+, CD36++, CD71+, CD45 –/+ with higher granularity (SSC) than mature erythroid cells. Basophilic erythroblasts also show reactivity for CD105, but they do not have expression of CD117, HLA-Dr, and have a brighter expression of CD36 and CD71 (Figure 1).2, 5 CD105 is not expressed on polychromatophilic, erythroblasts orthochromatophilic, and mature erythroid cells. The combination of CD235a, band3, and α4-integrin may also contribute to the differentiation between proerythroblasts (α4-integrin+ and band3 negative) and basophilic erythroblasts (α4-integrin+, and band3+/−).6 Therefore, CD105 in combination with CD36, CD71, CD117, HLA-DR, CD45, CD34, and CD235a may be considered a immunophenotypic strategy for the detection of erythroid progenitors and early erytrhoid precursors in myelodisplastic syndromes and PEL. Flow cytometric dot plots of normal erythroid differentiation from CD34+ cells in normal bone marrow. A small subset of CD34+ CD117+ cells (dark green dots) shows a progressive expression of CD105 and CD36 (CD34+ erythroid progenitors); proerythroblasts (red dots) are defined as CD34–/CD117+CD36+CD105+/CD71+/CD235a+, and basophilic erythroblasts (green dots) as CD34–CD117–CD36++CD105+CD71+CD235a+. CD105 is negative from polychromatophilic erythroblasts (blue dots) to the end stages of the erythropoiesis. Myeloid progenitors are CD34+CD117+HLA-Dr+CD105– (violet dots). [Color figure can be viewed at wileyonlinelibrary.com] Nothing to report.