The molecular basis of self-association of antibodies to IgG (rheumatoid factors) in rheumatoid arthritis.

The serum and synovial fluid of many patients with rheumatoid arthritis contain immune complexes composed of immunoglobulin G (IgG). In this study such complexes from one patient are shown to be formed by self-association of IgG-antibodies to IgG (IgG-rheumatoid factors), so that each molecule serves as an antibody as well as an antigen. All F(ab')(2) and Fab' fragments derived from these complexes have antibody binding sites for normal IgG. Due to a high association constant in the formation of a cyclic complex by these antibodies, normal IgG is excluded as an antigen. These studies serve as a model for further elucidation of presence of similar immune complexes in the serum and synovial fluid of patients with rheumatoid arthritis.