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 malign ant bone marrow (BM) by using the monoclonal antibody (mAb) AS-E1 dire cted against the transferrin receptor by flow cytometric (FCM) analysi s. 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 sub set (similar to 15%) expressing AS-E1(low). By fluorescence activated cell sorting, morphological examination of smears stained by immunocyt ochemistry and by BFU-E assays the AS-E1(high) fraction was shown to c ontain cells of erythroid origin (proerythroblasts, basophilic erythro blasts and polychromatic erythroblasts), whereas the AS-E1(low) fracti on consisted mainly of promyelocytes and myelocytes. In patients with malignant hematological disorders we found a more pronounced heterogen eity in the density and the degree of AS-E1(low) expression compared t o normal BM, and to further characterize the AS-E1(low) cells in patie nts and to exclude that this broad reactivity interfered with the iden tification of the AS-E1(high) cells, we employed triple-color FCM assa ys with mAbs directed against the myeloid surface markers CD13 and CD6 6 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 l ogAS-E1 density to be sufficient. We conclude that AS-E1(high) is a va lid FCM marker for the normal erythropoiesis.