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We investigated 86 synovial membranes from patients suffering either from rheumatoid arthritis (RA) or osteoarthritis (OA). Iron deposits in the synovial membrane were stained by the Prussian blue reaction, and the amount of stained iron was quantitatively assessed by microscope photometry. We found a statistically significant increase in iron deposits in the synovial membrane of RA patients when compared to OA patients. The amount of iron deposits correlated with the histological subtype of synovitis, those presenting with more exudative and proliferative features showing greater amounts of iron deposits. We also observed an inverse correlation between the haemoglobin concentration and erythrocytes in the serum and the amount of iron in the synovial membrane. From our data we concluded that iron deposits in the synovial membrane can contribute by several mechanisms, including activation of oxygen radicals, to the chronic inflammatory reaction in RA synovitis.

Lysozyme-producing cells were analysed by enzyme histochemistry in paraffin sections of synovial tissue of 60 patients with rheumatoid arthritis (RA) and 20 patients with osteoarthritis (OA). For lysozyme detection three enzyme histochemical systems - peroxidase-anti-peroxidase, alkaline phosphatase and biotin-avidin - were used in parallel experiments. Lysozyme was found to be produced by polymorphonuclear cells, mononuclear phagocytes and part of synovial lining cells. All types of lysozyme-producing cells were increased in RA compared with OA. Subgrouping of RA synovitis according to histomorphological criteria allowed the demonstration of an inverse relationship between the number of lysozyme-producing cells and the grade of proliferation of fibroblasts, called mesenchymoid transformation by Fassbender [19]. The different methods of lysozyme detection differed in specificity and sensitivity. The immunoenzymatic staining of lysozyme allows specific and quantitative evaluation of phagocytizing cells in RA and OA.