Humoral regulation of eosinophilopoiesis in vitro: analysis of the targets of interleukin-3, granulocyte/macrophage colony-stimulating factor (GM-CSF), and interleukin-5.

In order to delineate the humoral regulation of eosinophil production, we studied the effects of interleukin-3 (IL-3), granulocyte/macrophage colony-stimulating factor (GM-CSF), and interleukin-5 (IL-5), and their combinations on eosinophil colony formation in clonal cell culture. We plated 1,000 bone marrow null cells per dish and in some experiments used polyclonal anti-gibbon IL-3 sera and anti-human GM-CSF. IL-3 or GM-CSF independently from each other supported eosinophil colony formation. Although IL-5 supported formation of small eosinophil colonies, the number of colonies were significantly smaller than that supported by GM-CSF or IL-3. Cytological examination of the constituent cells revealed that some of the apparent eosinophil colonies supported by IL-3 and GM-CSF were mixed colonies containing eosinophils and one or more other lineages. In addition, the majority of the eosinophils seen in cultures with IL-3 and/or GM-CSF proved to be early eosinophil precursors including eosinophilic promyelocytes, myelocytes, and meta-myelocytes. IL-5-supported eosinophil colonies were pure eosinophil colonies and contained mostly maturer eosinophils such as band and segmented forms. These observations indicated that the developmental stages of the targets of IL-3 and GM-CSF are earlier than those of IL-5 and that the primary function of IL-5 is to support terminal maturation of eosinophils.