CSF1, 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 types of white blood cells essential for fighting infections and maintaining tissue health. CSF1 is produced by various cells in the body, including fibroblasts and endothelial cells. It binds to its receptor, CSF1R, on target cells, triggering signaling pathways that promote cell survival and proliferation. This process is vital for the proper functioning of the immune response and tissue repair.