Effects of interleukin-3 and erythropoietin on in vivo erythropoiesis and F-cell formation in primates

To test the in vivo cooperativity between interleukin-3 (IL-3) and erythropoietin (Epo) in stimulating erythropoiesis and hemoglobin F (HbF) production in primates, we administered recombinant human IL-3 and recombinant human Epo to baboons and macaques. The effect of these treatments was assessed by serial bone marrow cultures and by measuring HbF production in the progeny of bone marrow progenitors and in peripheral-blood reticulocytes. Administration of IL-3 alone to hematologically normal or anemic baboons produced an early increase in erythroid colony-forming units (CFUe) and erythroid clusters (e- clusters) with an increase in reticulocyte counts and a late increment in the relative frequency of erythroid burst-forming units (BFUe). In parallel to the increase in peripheral-blood reticulocytes, IL-3 increased the frequency of F reticulocytes in the normal and anemic animals. When administration of IL-3 was followed by administration of Epo, expansion in all classes of erythroid progenitors and increase in reticulocytes occurred, beyond the levels observed when the animals were treated with Epo alone. The combination of IL-3 and Epo, however, did not increase consistently the rate of F reticulocytes beyond the level induced by Epo alone. These results suggest that IL-3 enhances the effect of Epo on erythropoiesis, but the combination of the two growth factors does not lead to a preferential and significant enhancement of HbF production.