Macrophages as sources of hydrolases and other materials in chronic inflammation

Many inducers of inflammation, such as microorganism components, and asbestos, are potent stimulators of lysosomal enzyme secretion by cultured mouse peritoneal macrophages. Four major mechanisms of induction of prolonged acid hydrolase secretion by macrophages are now thought to exist: 1) Accompanying phagocytosis (though this has not been rigorously demonstrated); 2) Initiated within phagosomes by previously endocytosed materials; 3) Initiated at cell surface by ligard-plasma membrane interactions; 4) Pharmacologically induced secretion. Mechanisms 2 and 3 are probably particularly important in the maintenance of chronic inflammation, and also have bearing on neutral proteinase secretion. The release by stimulated macrophages of other materials such as alpha-2-macroglobulin (the general proteinase inhibitor), interferon and prostaglandins, which may be regulators of inflammatory processes is also outlined.