Characterization of IgG complexes in eluates from rheumatoid tissue.

Eluates of rheumatoid synovial and other rheumatoid granulation tissues both from seropositive and seronegative patients contained complexes of IgG, reacting with isolated IgM rheumatoid factor. According to gel filtration patterns, the molecular size of the complexes was similar to or even higher than that of heat-aggregated IgG. Patients with active disease and large amounts of IgG complexes in the tissue eluates often had low titres of free IgM rheumatoid factor both in eluates and in serum. This suggested an in vivo binding of IgM rheumatoid factor to tissue IgG complexes. A selection of Gm markers was observed in some eluates, compared to the corresponding markers in whole serum. The eluate IgG thus consisted partly of a restricted population of IgG molecules. After pepsin treatment of the IgG complexes to destroy Fc antigens, rheumatoid factor activity, not present in the untreated complexes, was revealed. This indicated that IgG antibodies to IgG took part in complex formation.