Synovial fluid ferritin in rheumatoid arthritis: an index or cause of inflammation?

In many inflammatory disorders excess iron is found within reticuloendothelial cells. In patients with rheumatoid arthritis the synovial membrane contains an excess of iron (in the form of ferritin) concentrated within the cytoplasm and lysosomes of the type A reticuloendothelial cells.1 The concept that this iron may promote or worsen inflammation is not new. de Duve2 suggested that lysosomes containing phagocytosed material discharge their enzymes more readily than do normal lysosomes. Muirden' suggested that incorporation of iron as ferritin in synovial cell lysosomes may facilitate enzyme release and promote tissue damage but failed to find a clear association between synovial membrane iron in rheumatoid patients and the degree of inflammation within the joints. We found large quantities of ferritin within the synovial fluid of patients with rheumatoid arthritis but not in those with osteoarthritis.3 This ferritin is presumably derived from the synovial reticuloendothelial cells. To establish whether synovial fluid ferritin concentrations reflect local reticuloendothelial activity we correlated synovial fluid ferritin concentration with other indices of synovial inflammation. As intra-articular immune complexes are considered to be responsible for perpetuating chronic synovitis in patients with rheumatoid arthritis we also looked at their association with synovial fluid ferritin concentrations.