CSF-1, or Colony Stimulating Factor 1, is a protein that plays a crucial role in the immune system. It is primarily involved in the growth and differentiation of monocytes and macrophages, which are essential white blood cells that help the body fight infections and clear debris. CSF-1 is produced by various cells, including fibroblasts and endothelial cells, in response to inflammation or tissue injury. By promoting the survival and proliferation of macrophages, CSF-1 helps maintain a healthy immune response and supports tissue repair processes in the body.