Receptors for recombinant erythropoietin in human bone marrow cells

Human recombinant erythropoietin, labelled with 125I, was saturably bound to high affinity receptors, ka = 1.5 X 10(9) M-1, of bone marrow cells from 10 patients with various haematological disorders. Binding of labelled erythropoietin was specific, with less than 0.01% cross-reactivities of TSH, hCG and renin substrate (angiotensinogen). Binding capacity averaged 3 X 10(-14) moles/10(6) cells. Binding was maximal within 30 min at 37 degrees C. Low binding, less than 15% of that to bone marrow cells, was found to peripheral blood buffy coat, while erythrocytes and BALL cells did not bind labelled erythropoietin. Autoradiography showed binding of label confined to 4-5% of the bone marrow cells.