Reticuloendothelial system

In anatomy, the reticuloendothelial system (abbreviated RES) is a network of immune cells distributed throughout the body that defends against foreign invaders, clears cellular debris, and recycles iron.

The term "reticuloendothelial system", more accurately called the mononuclear phagocyte system (MPS), was employed by the beginning of the 20th century to denote a system of specialised cells that effectively clear colloidal vital stains (so called because they stain living cells) from the blood circulation. The term is still used today but its meaning has changed over the years, and it is used inconsistently in present-day literature. Although RES is commonly associated exclusively with macrophages, recent research has revealed that the cells that accumulate intravenously administered vital stain belong to a highly specialised group of cells called scavenger endothelial cells (SECs) that are not macrophages.