IgG Complexes in Serum of Rheumatoid Arthritis Patients

Sera from 171 consecutive rheumatoid arthritis patients were tested for direct platelet aggregation. Thirty‐three of 146 rheumatoid factor (RF)‐positive sera and 3 of 25 RF‐negative sera gave platelet aggregation, indicating the presence of circulating IgG complexes equal to or greater than 19S. Forty randomly selected sera were analyzed by gel filtrations on Sepharose 4B and Sephadex G‐200 and by sedimentation analysis. IgG complexes, mainly of intermediate sizes, were demonstrated in 54% of sera with RF titers of 40 to 640 and in 80% of sera with an RF titer equal to or greater than 1280. The intermediate complexes could be absorbed on and eluted from cross‐linked human IgG, thus indicating IgG‐RF to be a dominant constituent of the complexes.