The effect of anti-lymphocytic IgG on estab- lished autoallergic thyroiditis in rats.

The autoallergic thyroiditis produced in rats by the injection of rat thyroglobulin in Freund's complete adjuvant can be suppressed by the administration of the IgG immunoglobulin fraction of heterologous (horse) anti-lymphocytic serum when treatment is started immediately after the antigen injection. In contrast anti-lymphocytic IgG failed to prevent the development of thyroiditis when given only 4 hr after the antigen nor did it show any suppressive effect on previously induced thyroiditis. Similar results were obtained when anti-lymphocytic IgG treatment was tested for its effect on the primary immune response to rat thyroglobulin.