The epidermal growth factor (EGF)-TM7 family constitutes a group of class B G-protein coupled receptors, which includes CD97, EMR1 (EGF-like molecule containing mucin-like hormone receptor 1, designated F4/80 in mouse), EMR2, EMR3, FIRE, and ETL (13). These family members are characterized by an extended extracellular region with several N-terminal EGF domains, and are predominantly expressed on cells of the immune system (13). The EGF-TM7 protein family are encoded by a gene cluster on human chromosome 19p13 (1,3,4). The F4/80 molecule is solely expressed on the surface of macrophages and serves as a marker for mature macrophage tissues, including Kupffer cells in liver, splenic red pulp macrophages, brain microglia, gut lamina propria, and Langerhans cells in the skin (1). F4/80/EMR1 undergoes extensive N-linked glycosylation as well as some O-linked glycosylation (5,6). The function of F4/80/EMR1 is unclear, but it is speculated to be involved in macrophage adhesion events, cell migration, or as a G-protein coupled signaling component of macrophages.
