Overview Article: the Articular Territory of the Reticuloendothelial System

It has long been recognized that synovial intimal cells are phagocytic and that they are capable of picking up colloidal or particulate material injected into the circulation. Hence they have been described as the "articular territory of the reticuloendothelial system." Ultrastructural studies have added a wealth new knowledge and details about the remarkable endocytotic powers of synovial cells. It has been shown that they can endocytose not only small particulate substances like colloidal iron, colloidal gold, and thorotrast but also relatively large objects like masses of fibrin and entire erythrocytes. Controversy has arisen as to whether it is the Type A or Type B cell that is the main scavenger of the joint. Evidence will be presented to show that this is a somewhat fictitious controversy and that these are not distinct and different races of cells with different functions but merely cells whose differences in morphology reflects the function they are performing at a given moment.