Immunocytology in arthritic joints.

The capacity of exudative neutrophils to phagocytose and digest fibrin, an important constituent of inflammatory exudates, was investigated in various types of arthritis. In addition, the catheptic enzyme content of inflammatory cells was established directly with the aid of fluorescent anticathepsin. The intracellular organization of cathepsin varied considerably among the patients. The distribution can be related to intracellular digestion of phagocytosed proteins and to release of cathepsin for extracellular proteolysis. From previous studies in dogs, we knew that exudative neutrophils exercise their phagocytic capacity to ingest and digest autologous fibrin during an experimental acute inflammation. Fibrin or something derived from it appeared to be a specific attractant for polymorphonuclear leucocytes. Furthermore, the continued addition of fibrin to the inflammatory site delayed the mononuclear cell entry that is so prominent in later stages of inflammation (Riddle and Barnhart, 1964). We wondered if a similar interrelationship between fibrin deposits and granulocytes might not exist within acute inflammatory sites in man. Joint disease offered an excellent source of inflammatory exudates to represent various stages of inflammation. The extent to which phagocytosis of fibrin occurred and the significance of its intracellular digestion as compared to the phagocytosis of other protein aggregates is the subject of this communication. Immunocytology identified the protein constituents of exudative leucocytes. With fluorescent markers specific for either fibrin, rheumatoid factor (IgM), gamma globulin (IgG), or albumin, we found that these substances were handled in different ways by exudative neutrophils from various arthritic patients. The significance of neutrophilic phagocytosis of fibrin and the role of fibrin per se in accounting for the persistence and recycling of acute inflammation becomes apparent from our work. Material and Methods