Exchange of IgM and albumin between plasma and synovial fluid in rheumatoid arthritis.

Most of the plasma proteins have been identified in normal synovial fluid (Schur and Sandson, 1963; Ropes and Bauer, 1953) but they are usually present in lower concentrations than those found in the plasma (Ropes and Bauer, 1953; Pekin and Zvaifler, 1964; Sundblad, Jonsson, and Nettelbladt, 1961). The higher molecular weight proteins, such as IgM macroglobulins, a2-macroglobulin, and fibrinogen, may not always be detectable. This synovial fluid protein pattern is altered in rheumatoid arthritis so that relatively greater concentrations of the high molecular weight components are present and quantitatively the constituent proteins more closely resemble plasma (Wilkinson and Jones, 1964; Perlmann, Ropes, Kaufmann, and Bauer, 1954; Schmid and MacNair, 1956; Vaughan, Jacox, and Noell, 1968). Recent studies (Rodnan, Eisenbeis, and Creighton, 1963; Hannestad and Mellbye, 1967; Barnett, Bienenstock, and Bloch, 1966) show similar titres for rheumatoid factor in plasma and synovial fluid, usually with slightly higher titres in plasma, or less commonly higher titres in synovial fluid. However, the precise distribution of rheumatoid factor IgM between plasma and synovial fluid can be only approximated by serological titration. There have been few reports (Rodnan and Maclachlan, 1960; Kuipers, Francke, and Robert, 1956; Ahlstrom, Gedda, and Hedberg, 1956; Oeff, 1960) of dynamic studies of the distribution of proteins between synovial fluid and plasma. This investigation is an attempt to follow the metabolism and distribution of radioiodinated IgM in the plasma and synovial fluid of six patients with rheumatoid arthritis, using a group of highly purified cold agglutinins as a source of IgM macroglobulin. IgM was chosen because of its high molecular weight, and its rele-