Electron microscopy of the spleen. II. Phagocytosis of colloidal carbon.

COLLOIDAL PrCLES, such as carbon, have been used for many years to study the physiology and phagocytic capacities of the reticuloendothelial system.1J The method by which thle particulate matter is cleared from the blood has been deemed important because of its analogy to septicemia and to the clearance of antigens in immunologic reactions.3 Altlough ffiere have been a considerable number of studies on the physiology of reticuloendothelial phagocytosis, there have been relatively few ultrastructural studies and most of these have concentrated on the liver and not on the spleen.4'0 The only electron microscopic studies emphasiing splenic phagocytosis have been concerned with reticuloendothelial blockade'" or anatomical investigations.12"13 Tracers have also been used to localiz and follow the movement of antigen within the spleen at different periods following injection. The distribution of I2' labelled Salmonella flagellar antigen has been compared with that of carbon particles.'4"5 Bot Salmonella antigen and carbon accumulate initially in the red pulp and marginal zone but differ in their final localization. This movement of tracer containing macrophages has not been verified with the electron microscope in the spleen. Nor have there been any studies to determine if it is only the macrophages that migrate, or whether, for example, the splenic endothelial cells also participate in any migration and phagocytmis. It is also curious that there have been more studies of phagocytosis by endothelial cells outside the reticuloendothelial system.161'