T cell competence to heterologous and homologous thyroglobulins during the induction of experimental autoimmune thyroiditis.

The ability of T cells to respond to homologous vs. heterologous thyroglobulins (Tg) has been evaluated using different models for the induction of experimental autoimmune thyroiditis. Substantial levels of T cell activation could be demonstrated to heterologous Tg following immunization with heterologous Tg in complete Freund's adjuvant, whereas only minimal levels of T cell activation to homologous Tg could be obtained following immunization with homologous Tg in complete Freund's adjuvant. Using this immunization protocol, heterologous and homologous Tg induced equivalent levels of serum antibody to the immunizing Tg. However, when injected in incomplete Freund's adjuvant, homologous Tg induced less antibody than heterologous Tg. Even greater differences in serum antibody levels to heterologous and homologous Tg, were apparent following immunization with soluble Tg. These thyroiditis differences are attributed to the presence of only a minimal level of T cell competence for homologous Tg, which is capable of inducing experimental autoimmune thyroiditis with stringent immunization protocols, but not with weaker immunization regimens.