Studies of the reticuloendothelial system (RES). I. Measurement of the phagocytic capacity of the RES in man and dog.

In 1884, Metchnikoff (1) presented his studies of phagocytosis and concluded that the process was a general reaction that removed particulate matter from the circulation. Highly mobile cells, the polymorphonuclear leukocytes, were observed to ingest microorganisms and other particulate matter, such as pus, corpuscular elements of extravasated blood, and foreign cells. In addition to these circulating phagocytes, or microphages, certain "reticulum" cells lining the blood and lymph spaces were observed to engulf circulating particulate matter. These fixed phagocytes were designated subsequently by Aschoff (2) as the reticuloendothelial system (RES), comprising the Kupffer cells of the liver, cells lining the sinuses of the spleen, lymph nodes, and bone marrow, and endothelial cells of various other organs. To examine phagocytosis in experimental animals, one may use colloidal particles such as carbon, thorium dioxide (Thorotrast), saccharated iron oxide, and more recently, radioactive chromic phosphate, colloidal gold, or colloidal silver. Although they have yielded important information, studies with these inorganic colloidal substances have been of limited value in the study of human disease. Because the body cannot metabolize these particles, they remain in the RES almost indefinitely, and only trace quantities can be administered safely to human subjects. Since the rate of removal of trace quantities of particles from the circulation depends primarily on the blood flow to reticuloendothelial cells, the greatest usefulness of previously available colloidal particles has been in the measurement of liver blood flow.