Immunopathological changes in rheumatoid arthritis and other joint diseases.

A comparative study of the distribution of immunoglobulins G, M, and A and C3 in the synovium and inside synovial fluid leucocytes and of the relative levels of IgG, IgM, AND C3 in paired samples of serum and synovial fluid from both seropositive and seronegative patients with rheumatoid arthritis and other types of non-infective synovitis shows that although there is no distinctive immunopathological feature of rheumatoid arthritis, the incidence of immune complexes containing IgG and IgM with and without detectable C3 in the affected synovium or inside synovial fluid granulocytes is higher in rheumatoid arthritis and especially so in seropositive cases. The mean level of C3 in synovial fluid from patients with rheumatoid arthritis is lower than that from the group without rheumatoid arthritis. In contrast to previous reports, extracellular clumps of IgA could be detected in the affected synovium of a number of affected patients. Aggretated human IgG could be bound by some of the synovial biopsies and synovial fluid leucocytes from both seropositive and seronegative rheumatoid arthritis patients. Antinuclear factor and rheumatoid factor could be detected in the synovial fluid but not in the serum of several patients suggesting either selective sequestration or local synthesis of antinuclear and rheumatoid factors in the affected joints.