Transferrin iron uptake by human synovium

SUMMARY 55Fe-labelled transferrin was injected into the synovial fluid before synovectomy in 6 patients with rheumatoid arthritis. The results show that transferrin iron is taken up by synovial macrophages. The synovium of patients with rheumatoid arthritis contains more than the normal amount of stainable iron (Mowat and Hotherstall, 1968; Muirden and Senator, 1968) despite the frequent presence of anaemia and sideropenia. In this respect the synov-ium mimics the reticuloendothelial iron stores of the marrow which in this disease may also contain increased quantities of iron. The marrow iron may come from the breakdown of worn out red cells, while in the synovium local bleeding as a result of joint damage may supply iron to the tissue macro-phages. It is, however, possible that cells of the reticuloendothelial system may take up at least some of their iron from transferrin. Although Lynch et al. (1974) concluded that reticuloendothelial cells do not take up iron from transferrin, other workers (MacSween and MacDonald, 1969; O'Shea et al., 1973) have shown that iron uptake from transferrin is possible in vitro. This study was undertaken to investigate whether synovial tissue macrophages can take up labelled transferrin iron in vivo and hence whether their intracellular iron could be in part derived from the same source. Methods The study was carried out in 6 patients who were to undergo synovectomy. All were suffering from classical or definite rheumatoid arthritis (Ropes et al., 1959). Their haemoglobin concentrations were between 13 g/dl and 14 g/dl, with a mean corpuscular volume of 77-88 fl. Fully informed consent to participate in this study was obtained from each patient. Approximately 2 hours before operation 10 ml venous blood was taken from each patient and the plasma transferrin labelled with 55Fe by the metho