Description: G-CSF (Granulocyte colony-stimulating factor) is a growth factor that stimulates the proliferation, differentiation, and mobilization of hematopoetic stem cells. It is expressed by monocytes, macrophages, and bone marrow stromal cells, and can also be induced in fibroblasts by IL-17A. Unlike GM-CSF and IL-3, which can stimulate cells of multiple lineages, G-CSF activity is limited to neutrophilic granulocytes. G-CSF is essential to the maintenance of neutrophil counts during homeostasis, and low basal levels of the protein are detectable in the serum of healthy individuals. Circulating levels become elevated rapidly upon infection, as G-CSF is also important for the activation and mobilization of mature neutrophils during the innate immune response. G-CSF therapy is commonly used to treat neutropenia following bone marrow transplant or chemotherapy.