19S IgM rheumatoid factor-7S IgG rheumatoid factor immune complexes isolated in sera of patients with juvenile rheumatoid arthritis

19S IgM rheumatoid factors (RF) and hidden 19S IgM RF have been associated with increased disease activity in juvenile rheumatoid arthritis (JRA). Recently, immune complexes (IC) were isolated from JRA sera by several methods which demonstrated the presence of 19S IgM RF. The present study evaluates 25 JRA patients’ sera by separation on a Sepharose 4B column to which were bound F(ab’)₂ fragments of goat IgG anti-human IgM antibody to separate IgM-containing IC. The columns were sequentially eluted with 1 M ammonia and 0.1 M glycine-HCl buffer, pH 3.0. The isolated fractions were assayed for 19S IgM RF and 7S IgM RF by ELISA, IgG levels by immunodiffusion, and by preparative isoelectric focusing. The ammonia eluate from the aHIgM column revealed IgG, 19S IgM RF in six patients, and IgM RF in four patients. All were polyarticular-onset JRA patients. In the glycine-HCl eluate of sera, 19S IgM RF and IgG were also detected in 15 patients, all six seropositive, polyarticular-onset, six seronegative, polyarticular-onset, and three pauciarticular-onset patients. Significant 7S IgG RF titers were demonstrated in the glycine-HCl eluates of six patients, five seropositive, polyarticular-onset patients, and one seronegative, polyarticular-onset patient. Analysis by preparative isoelectric focusing of the IgM RF and IgG RF positive ammonia and glycine-HCl eluates showed IgM RF throughout the pH range (4-10), but the highest amount of IgM RF was in the pH range 4.0-5.5. Significant IgG RF titers were detected only in this restricted spectro-typic area of pH 4.0-5.5. These studies demonstrate IC-containing 19S IgM RF-IgG and 19S IgM RF-7S IgG RF can be detected in JRA patients’ sera. The 19S IgM RF and IgG RF when present are predominantly found in the pH band 4.0-5.5 by preparative isoelectric focusing. The ability to isolate IC containing 19S IgM RF as a marker in this pH band may relate to active disease. Further determination of the constituents of the IC may help in defining the antigen in JRA and understanding the pathophysiologic mechanisms of the disease.