Molecular analysis of complement-fixing rheumatoid synovial fluid immune complexes.

The characteristics of the solid-phase conglutinin method for the isolation of C3-containing complexes from the synovial effusions of rheumatoid arthritis patients were assessed. All major proteins in such complexes were identified and shown to be either immunoglobulin or complement components. The high proportion of IgM and the association between complexed IgM and latex agglutination titre suggest that IgM rheumatoid factor, probably binding to self-associated IgG antiglobulins, is of major importance in the formation of complement-fixing complexes. A minority of samples contained unidentified trace components and these differed from one fluid to another. The levels of complexed immunoglobulins were closely correlated to the titres of synovial fluid antiglobulins. The data accords with the view that autosensitization to IgG plays the primary role in the development of immunopathological features of rheumatoid arthritis.