Interleukin-3 and interleukin-1α allow earlier bone marrow progenitors to respond to human colony-stimulating factor 1

By using human bone marrow cells enriched for early progenitors by selective immunoadsorption and plated at low cell density (10³ to 10⁴ cells/mL/9.6 cm²) in semisolid methylcellulose culture, we have analyzed the cooperative effects of human colony-stimulating factor 1 (CSF-1), granulocyte-macrophage-CSF (GM-CSF), interleukin-1α (IL-1α), and gibbon as well as human recombinant IL-3 on the formation of monocytic colonies. CSF-1 alone stimulated mature monocytic colony formation by human CFU-M. However, in the presence of IL-3 and erythropoietin, CSF-1 stimulated maximal immature monocytic colony formation at low concentrations and inhibited the formation of granulomonocytic, erythrocytic, and mixed colonies. Cultures with CSF-1 and IL-3 contained more immature monocytic colonies than did cultures with CSF-1 alone. IL-1α alone had little effect. However, IL-1α in combination with optimal concentrations of either CSF-1, GM-CSF, or IL-3 increased the number of colonies containing immature or mature monocytic colonies.