Granulocyte Colony-Stimulating Factor (G-CSF), also known as CSF-3 and MGI-1G, is a cytokine and hormone belonging to the IL-6 superfamily. It is expressed by monocytes, macrophages, endothelial cells, fibroblasts and bone marrow stroma. G-CSF stimulates the bone marrow to produce granulocytes and stem cells, and specifically stimulates the proliferation and differentiation of the neutrophilic granulocyte lineage. G-CSF has been used to stimulate white blood cell production after chemotherapy. It has also been used to boost the number of hematopoietic stem cells after bone marrow transplantation.