[1][2][3] In the 1920s, the originator of the term RES, Ludwig Aschoff, reviewed the field of vital staining, and concluded that the cells lining the hepatic sinusoids are by far the most numerous and important cells accumulating intravenously administered vital stains in mammals and other vertebrates.
Cells lining the lymph sinuses, and the capillaries of the adrenals, pituitary and bone marrow also accumulated vital stains, yet to a lower extent.
Based on these observations Aschoff in his review concluded that these were the organs housing the cells of the RES, in the narrow sense of the term.
During the years that followed after Aschoff had originated the concept of RES, research on macrophages and their role as phagocytes steadily increased, and in 1960 the concept of the mononuclear phagocyte system was proposed to denote all cells identified as macrophages.
In 1998 experiments were carried out to repeat the studies of Aschoff, following exactly the original methods description, and using modern ways of identifying the cells that were responsible for clearance of intravascularly injected colloidal lithium carmine, the most commonly used vital stain.