β2‐Microglobulin‐containing IgG Complexes in Sera and Synovial Fluids of Rheumatoid Arthritis and Systemic Lupus Erythematosus Patients

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Abstract
The occurrence and composition of complexed β2-microglobulin (β2m) In sera and synovial fluids of rheumatoid arthritis and systemic lupus erythematosus patients and control persons was investigated. β2m-containing complexes were detected In immune complex (IC)-enriched fractions isolated by precipitation with 3% polyethylene glycol 6000, In the macromolecular peaks after Sephadex G-200 gel filtration, and in IC desorbed from solid-phase Clq. β2m complexes were demonstrated also after precipitation of redissolved PEG-insoluble material by anti-human β2m serum or isolation of the complexes by use of Sephadex-anti-β2m. IgG was co-isolated with with β2m on Sephadex-anti-β2m, and free β2m inhibited the binding of IgG to Sephadex anti-β2m, Indicating that IgG was present in the complexed β2m. Analysis by SDS–polyacrylamide gradient electrophoresis under reducing conditions indicated that the purified β2m complexes contained IgG and β2m.