Feline Macrophage Colony-Stimulating Factor (M-CSF) is a cytokine that regulates the development, proliferation, and survival of monocytes and macrophages in cats (Felis catus). M-CSF is produced by a variety of cell types, including fibroblasts, endothelial cells, and stromal cells, in response to tissue signals and inflammatory stimuli. Feline M-CSF binds to the colony-stimulating factor-1 receptor (CSF1R), a receptor tyrosine kinase expressed on monocytes and macrophage lineage cells, activating intracellular signaling pathways such as PI3K–AKT, ERK/MAPK, and JAK–STAT that promote differentiation and maintenance of macrophage populations. Through these mechanisms, M-CSF supports macrophage-mediated immune surveillance, phagocytosis, tissue homeostasis, and inflammatory responses. Because macrophages play a central role in controlling infection and regulating inflammation, M-CSF–mediated macrophage function is important for maintaining overall immune health and disease resistance in cats. In cell culture, recombinant feline M-CSF is commonly used to promote differentiation of feline monocytes into macrophages and to support macrophage proliferation and functional assays in vitro. Feline M-CSF is also studied in animal model research, including investigations of macrophage responses during feline infectious diseases such as feline immunodeficiency virus (FIV) and feline infectious peritonitis (FIP), helping researchers better understand macrophage biology and host–pathogen interactions.