Macrophage Colony-Stimulating Factor (M-CSF) is a protein that plays a crucial role in the immune system. It is primarily responsible for the growth and differentiation of macrophages, which are essential white blood cells that help the body fight infections and clear away dead cells. M-CSF is produced by various cells, including fibroblasts and endothelial cells, in response to inflammation or injury. M-CSF binds to its receptor, known as CSF1R, on the surface of precursor cells in the bone marrow, promoting their development into macrophages. This process is vital for maintaining a healthy immune response and ensuring that the body can effectively respond to pathogens and tissue damage.