Which of the following precursors are target cells for IL-3?

• A. Myeloid precursors
• B. Lymphoid precursors
• C. Erythroid precursors
• D. All of the above

Answer: (D)

IL-3 is a broad-spectrum hematopoietic growth factor that acts on early progenitor cells, not just a single lineage. Because it targets multipotent progenitors, it promotes the growth and differentiation of colonies that give rise to multiple lineages, including erythroid and myeloid, and it can influence early precursors that can lead to lymphoid cells as well. In practice, IL-3 supports colonies like CFU-GEMM (which includes granulocytes, erythrocytes, monocytes, and megakaryocytes) and BFU-E, reflecting its action on both red cell and myeloid pathways. Its receptor combines subunits used by GM-CSF and IL-5, enabling a broad responsiveness across these early cells. Therefore, all of the listed precursor types can respond to IL-3, making the best choice all of the above.