F4/80, also known as EMR1 and Ly71, is an extensively glycosylated multi-pass transmembrane protein that is part of the EGF-TM7 family of adhesion molecules. Mouse F4/80 is 931 amino acids (aa) in length with a predicted molecular weight of approximately 160 kDa. It shares 68% aa sequence identity with the human homolog, EGF-like Module-containing Mucin-like Hormone Receptor-like 1 (EMR1). It contains seven EGF-like domains and a GPS domain. F4/80 is a well-characterized mature mouse macrophage marker that is expressed on several tissue macrophages including Kupffer cells, gut lamina propria, splenic red pulp macrophages, Langerhans cells, and microglia. In humans, EMR1 is restricted to eosinophils. It has been suggested that F4/80 plays a role in the development of peripheral tolerance.