In vitro characterization of synthesized thyroglobulin immune complexes (IC). A model for studies of IC containing an autoantigen.

Human thyroglobulin (Tg) immune complexes (TgIC) were preformed at different ratios from purified Tg, and Tg antibodies (TgAb) obtained from six patients with autoimmune thyroid diseases. TgIC were characterized by precipitation with polyethylene glycol, and sedimentation in sucrose gradient. TgIC from one patient were further characterized by concanavalin A (con A), and binding to the complement factor Clq and rheumatoid factor (RF). Tg and TgIC had almost identical binding to con A, no binding to Clq, but could be partially separated by ultracentrifugation and polyethylene glycol. The highest degree of separation was obtained by a RF-coated plastic tube radiometric assay, using 125-I-rabbit TgAb as indicator. Tg showed no binding to RF, and a dose-response curve of TgIC in serum could be established. There was a dependence of the Tg-TgAb ratio, TgIC at equilibrium and in antibody excess being detected most efficiently. The method may serve as an aid in the evaluation of the fate of Tg, TgAb and TgIC following thyroid damage (surgery, radioiodine) and may be extended as a model system in the investigation of immune complexes in connection with autoimmune disorders.