Light and electron microscope studies in carragheenin, adjuvant, and tuberculin-induced arthris.

The classical descriptions of the pathology of rheumatoid arthritis have largely come from autopsy studies in far advanced disease. The frequent use of surgery in recent years has stimulated much interest in the synovial changes by providing material from the earliest proliferative stages. Features previously unrecognized, such as a "distinctive" synovial giant cell, have been described in seropositive rheumatoid disease (Grimley and Sokoloff, 1966), whilst rarely mentioned deposits of iron in the joints have been shown to be an almost constant finding (Muirden and Senator, 1968). Access to biopsy material has permitted the immediate fixation necessary for electron microscopic examination. Barland, Novikoff, and Hamerman (1964) first described the presence of large cyctoplasmic granules or lysosomes in the A type lining cells. Our own studies have emphasized the frequency of ferritin deposits in these cells and a complex cytoplasmic body containing ferritin which seemed characteristic of the material examined has been described (Muirden, 1966). It has often been stated, however, that unlike the rheumatoid nodule the pathological changes in the synovium in rheumatoid arthritis cannot be considered specific for the disease (Collins, 1949). In this report it will be shown that this remains true. The "distinctive" synovial giant cell, the iron deposits, the distribution of iron within the cell, the lysosomal enlargement, and the "characteristic" lysosome containing ferritin can all be found in forms of experimental arthritis in animals. This applies to the arthritis induced by the mucopolysaccharide carragheenin, which produces its effect by chemical irritation, as well as to the adjuvant and tuberculininduced arthritis which involve immunological mechanisms.