Granulocyte-Colony Stimulating Factor (G-CSF) is a cytokine that functions as a potent inducer of neutrophilic granulocyte proliferation, terminal differentiation, and activation. G-CSF synthesis occurs in monocyte, macrophage, epithelial, endothelial, and fibroblast cells after activation by bacterial endotoxins, Tumor Necrosis Factor α (TNF-α), Interleukin-1 (IL-1), or Interleukin-17 (IL-17). The functional activity of G-CSF is mediated through the granulocyte colony-stimulating factor receptor (G-CSF-R) to activate JAK/STAT and MAPK signal transduction pathways. G-CSF also promotes neurogenesis and inhibits neuronal apoptosis. Human and mouse G-CSF proteins are cross-reactive.