Sedimentation Characteristics of Human Thyroid Autoantibodies

Forty-six sera from patients with Hashimoto's thyroiditis were separated into 7S and 19S fractions by zone ultracentrifugation over sucrose density gradients. In each case at least 98 per cent of the anti-thyroglobulin activity was recovered in the 7S fraction. This was confirmed by chromatography on DEAE-cellulose. This also revealed significant antibody activity in a 7S γ-globulin fraction of fast electrophoretic mobility obtained from one serum giving a `clear' line on reaction with thyroglobulin in agar gel. Complement-fixing antibodies reacting with the thyroid microsomal fraction were also of low molecular weight. Thyroglobulin autoantibodies induced experimentally in rats were confined to the 7S fraction of serum. Initially, rabbits respond to the intravenous injection of human thyroglobulin with the production of 19S antibodies but by the 15th day, predominantly 7S antibodies are found.