The cloning and expression of the gene for ovine interleukin-3 (multi-CSF) and a comparison of the in vitro hematopoietic activity of ovine IL-3 with ovine GM-CSF and human M-CSF.

The ovine interleukin-3 (IL-3) gene has been cloned. It encodes a protein 146 amino acids (aa) in length and is situated approximately 10 kb from the gene encoding granulocyte-macrophage colony-stimulating factor (GM-CSF). A comparison of the ovine gene sequence with that of the human IL-3 gene reveals that the protein coding regions share between 49 and 59% identity, while the introns and other noncoding regions share between 63 and 78% identity. The gene promoters also share approximately 72% identity. Recombinant ovine IL-3 (rovIL-3) was expressed in Chinese hamster ovary (CHO) cells, and its biologic activity was compared to that of rovGM-CSF and recombinant human macrophage colony-stimulating factor (rhM-CSF) on ovine bone marrow cells. rovIL-3 predominantly stimulated the growth and development of mast cells and macrophages in liquid cultures and colonies of mixed cell phenotype, megakaryocytes, erythroid burst-forming units (BFU-E), and basophilic granular cells in soft agar cultures of bone marrow cells. In common with rovGM-CSF, IL-3 also stimulated eosinophil and macrophage colonies, which were increased in size and number of cells in cultures containing both cytokines. Maximum macrophage colony numbers were achieved with the combination of rovIL-3, rovGM-CSF, and rhM-CSF. rovGM-CSF stimulated neutrophil colony formation, whereas rovIL-3 did not.