Delineation of erythropoiesis in normal and malignant bone marrow using monoclonal antibody AS-E1 directed against transferrin receptors (CD71).

We have delineated the erythropoietic compartment in normal and malignant bone marrow (BM) by using the monoclonal antibody (mAb) AS-E1 directed against the transferrin receptor by flow cytometric (FCM) analysis. In normal BM we found a bimodal expression in antigen density with a minor subset (similar to 3%) expressing AS-E1(high) and a larger subset (similar to 15%) expressing AS-E1(low). By fluorescence activated cell sorting, morphological examination of smears stained by immunocytochemistry and by BFU-E assays the AS-E1(high) fraction was shown to contain cells of erythroid origin (proerythroblasts, basophilic erythroblasts and polychromatic erythroblasts), whereas the AS-E1(low) fraction consisted mainly of promyelocytes and myelocytes. In patients with malignant hematological disorders we found a more pronounced heterogeneity in the density and the degree of AS-E1(low) expression compared to normal BM, and to further characterize the AS-E1(low) cells in patients and to exclude that this broad reactivity interfered with the identification of the AS-E1(high) cells, we employed triple-color FCM assays with mAbs directed against the myeloid surface markers CD13 and CD66 in addition to AS-E1. In all patients we found that 80-90% of the AS-E1(low) cells co-expressed CD13 and/or CD66 and thus were of myeloid origin. Finally, we evaluated 2 methods for determination of the AS-E1(high) subset and found an assay involving forward light scatter and logAS-E1 density to be sufficient. We conclude that AS-E1(high) is a valid FCM marker for the normal erythropoiesis.