Regulation of macrophage phagocytosis.

The removal of pathogens from the circulation is achieved primarily by cells of the mononuclear phagocyte system, also known as the reticuloendothelial system. The tissue macrophage is the most important component of this system. The phagocytic activity of macrophages is regulated by opsonins on pathogenic materials and by endogenous cytokines. A number of diseases are caused by qualitative or quantitative disorders of phagocytosis by four major mechanisms: a decrease in the flow of blood to organs which contain macrophages (e.g. congestive heart failure and portal hypertension); a decrease in the quantity of tissue which contains macrophages (e.g. hepatic cirrhosis and splenectomy); a decrease in the effective opsonization of pathogens because of a deficiency of complement or IgG; and qualitative dysfunction of macrophages due to a deficiency of regulatory cytokines (e.g. gamma interferon and tuftsin) or a direct inhibitory effect on the macrophage (e.g. viral infections). New approaches for selective regulation of the phagocytic activity of macrophages are emerging.