Immunoregulation of experimental autoimmune thyroid disease

Verginis, Panayotis (2005) Immunoregulation of experimental autoimmune thyroid disease. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Experimental autoimmune thyroiditis (EAT) can be induced in mice after challenge with thyroglobulin (Tg) in complete Freund's adjuvant (CFA). EAT resembles Hashimoto's thyroiditis (HT) in humans and is characterized by mononuclear cell infiltration of the thyroid gland leading to hypothyroidism. -- In the first part of this study, we attempted to delineate pathogenic Tg peptides that encompass dominant epitopes in order to study immunoregulation mechanisms in EAT. Since susceptibility to EAT is under the control of H-2A k genes, we utilized an algorithm-based approach that predicts peptides with Ak -binding potential. Five Tg peptides were found to induce EAT in CBA/J (H-2k) mice. In addition, all five peptides were immunogenic at the T cell level and induced production of IL-2 and IFN-[gamma] by peptide-primed LNCs. Although none of these Tg peptides encompass dominant epitopes, they will allow us to study mechanisms involved in the immunoregulation of EAT. Furthermore, one of the five new Tg peptides (a.a. 2596-2608), was pathogenic in H-2k strains of diverse non-H-2 background but not in mice of q, s, d, and b haplotypes. The above findings provide important information regarding the influence of H-2 and non-H-2 genes in the thyroiditogenic potential of the Tg peptides. -- In the second part of this study, we showed that TNF-[alpha]-treated, semimature DCs pulsed with Tg, but not with OVA antigen suppressed Tg-induced EAT in CBA mice, through the induction of Tg-specific CD4+ CD25 + T cells. These CD4+ CD25+ Treg cells produce high levels of IL-10 and inhibit the proliferation of Tg-specific effector cells in vitro. Suppression was shown to be cytokine-independent but cell-cell contact dependent. Additionally, adoptive transfer of the CD4 + CD25+ Treg cells into CBA hosts suppressed Tg-induced EAT confirming the suppressogenic potential of this cell subset. The induction of antigen-specific Treg cells will contribute to understand the mechanisms involved in the immunoregulation of autoimmune diseases. -- Finally, we describe the generation of transgenic mice specific for the p2496 pathogenic Tg epitope. The [alpha] and [beta] chain of a p2496-specific I-As -restricted T cell hybridoma were identified and inserted into TCR expression vectors. Linearized fragments containing the [alpha] and [beta] chain genes and the constant chain regions were injected into fertilized oocytes of (SJLxC57BL6) mice and integration of the transgene was monitored by PCR. The p2496-specific TCR transgenic mice will provide an excellent source of p2496-specific naïve T cells that will be used to answer questions on the maintenance of self tolerance. In addition it allow the study of parameters that lead to activation of the autoractive T cells and initiation of EAT.

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