Isolation and characterization of circulating immune complexes in patients with rheumatoid arthritis

We studied soluble immune complexes in sera and synovial fluids of ten patients suffering from Rheumatoid Arthritis (RA), six seropositive and four seronegative. Isolation of the immune complexes was obtained by a combination of gel filtration and affinity chromatography from biological fluids. The first step involved preparation of a globulin-enriched fraction by precipitation of either serum or synovial fluid with 5% polyethylene glycol 6000. The precipitate was solubilized in Borate NaCl buffer and fractioned by gel filtration in Ultrogel AcA 34. Eluted peaks were submitted to affinity chromatography on a Protein A-Sepharose CL 4B column. The recovered material was analyzed by double immunodiffusion and electrophoresis in 6-20% polyacrylamide gel containing sodium dodecylsulphate (SDS-PAGE) and was shown to contain IgG, IgM, IgA with small amounts of C1q, C3 and C4. Observation occurred that there is a different distribution of macromolecular and intermediate complexes in seropositive and seronegative samples respectively, total C1q binding activity being equal.