F4/80, also known as ADGRE1 or EMR1, is a cell surface glycoprotein and a member of the EGF-TM7 protein family. It is widely used as a marker for mature mouse macrophages and is highly expressed in various macrophage populations, such as Kupffer cells in the liver, Langerhans cells in the skin, and microglial cells in the brain. However, its expression in human cells is different, being mainly found in eosinophils and some macrophages. F4/80 is an orphan receptor involved in cell adhesion and immune cell interactions, and it may also play a role in the development of regulatory T cells. The protein has a large extracellular domain containing multiple EGF-like calcium-binding domains, linked to a seven-transmembrane domain characteristic of G protein-coupled receptors.