Granulocyte-colony stimulating factor (G-CSF) is a naturally occurring protein that stimulates the production of white blood cells, specifically neutrophils. It plays a crucial role in the immune system by enhancing the body's ability to fight infections. G-CSF is produced by various cells in the body, including macrophages and fibroblasts, in response to inflammation or infection. In medical settings, synthetic forms of G-CSF are used as a treatment to boost white blood cell counts in patients undergoing chemotherapy or those with certain blood disorders. This helps reduce the risk of infections and allows for more effective cancer treatment.