Expression and characterization of erythropoietin receptors on normal human bone marrow cells

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Abstract
We studied the specific binding of 125I‐labeled bioactive recombinant human erythropoietin (Epo) to human bone marrow mononuclear cells (BMNC) obtained from normal subjects. The 123I‐labeled Epo bound specifically to the BMNC. Scatchard analysis of the data showed two classes of binding sites; one high affinity (Kd 0.07 nM) and the other low affinity (Kd 0.38 nM). The number of Epo binding sites per BMNC was 46 16 high‐affinity receptors and 91 51 low‐affinity receptors. The specific binding was displaced by unlabeled Epo, but not by other growth factors. Receptor internalization was observed significantly at 37C, but was prevented by the presence of 0.2% sodium azide. These findings indicate that human BMNC possess two classes of specific Epo receptors with characteristics of a hormone‐receptor association.