Interleukin 3 (IL-3) encoded by the IL3 gene is a cytokine secreted by basophils and activated T cells to support growth and differentiation of T cells from the bone marrow in an immune response. IL-3 stimulates the differentiation of multipotent hematopoietic stem cells into myeloid progenitor cells or, with the addition of IL-7, into lymphoid progenitor cells. In addition, IL-3 stimulates proliferation of all cells in the myeloid lineage (granulocytes, monocytes, and dendritic cells), in conjunction with other cytokines, e.g., erythropoietin (EPO), granulocyte macrophage colony-stimulating factor (GM-CSF), and IL-6.