Recruitment of multiple V beta genes in the TCR repertoire against a single pathogenic thyroglobulin epitope

Tolerogenic semimature dendritic cells suppress experimental autoimmune thyroiditis by activation of thyroglobulin-specific CD4+CD25+ T cells

Ex vivo treatment of bone marrow-derived dendritic cells (DCs) with TNF-alpha has been previously shown to induce partial maturation of DCs that are able to suppress autoimmunity. In this study, we demonstrate that i.v. administration of TNF-alpha-treated, semimature DCs pulsed with thyrogloblin (Tg), but not with OVA Ag, inhibits the subsequent development of Tg-induced experimental autoimmune thyroiditis (EAT) in CBA/J mice. This protocol activates CD4(+)CD25(+) T cells in vivo, which secrete IL-10 upon specific recognition of Tg in vitro and express regulatory T cell (Treg)-associated markers such as glucocorticoid-induced TNFR, CTLA-4, and Foxp3. These CD4(+)CD25(+) Treg cells suppressed the proliferation and cytokine release of Tg-specific, CD4(+)CD25(-) effector cells in vitro, in an IL-10-independent, cell contact-dependent manner. Prior adoptive transfer of the same CD4(+)CD25(+) Treg cells into CBA/J hosts suppressed Tg-induced EAT. These results demonstrate that the tolerogenic potential of Tg-pulsed, semimature DCs in EAT is likely to be mediated through the selective activation of Tg-specific CD4(+)CD25(+) Treg cells and provide new insights for the study of Ag-specific immunoregulation of autoimmune diseases.

Flexibility of TCR repertoire and permissiveness of HLA-DR3 molecules in experimental autoimmune thyroiditis in nonobese diabetic mice

Experimental autoimmune thyroiditis (EAT) is inducible in genetically susceptible mice by immunization with mouse thyroglobulin (mTg). With susceptibility linked to MHC class II, EAT is useful in studying human leukocyte antigen (HLA) associations with Hashimoto's thyroiditis. In non-obese diabetic (NOD) mice, approximately 10% thyroiditis incidence occurs with aging. This potential was exploited to examine the T cell repertoire and HLA association in EAT. Similar to B10.K-Vbeta(c)mice with TCRBV genes reduced by approximately 70%, mTg-immunized NOD-Vbeta(c)mice developed thyroiditis comparable to controls, indicating plasticity of the TCR repertoire for pathogenic epitopes. HLA association was evaluated by introducing HLA-DRA/DRB1*0301 (DR3) transgene into class II-negative NOD mice (Ab(0)/NOD). Previously, this HLA-DR3 transgene rendered EAT-resistant B10.M and Ab(0)mice susceptible to both mTg- and hTg-induced EAT. These results are now confirmed. mTg-induced thyroiditis in DR3+ Ab(0)/NOD mice was comparable to that in NOD and DR3- NOD mice, and the proliferative response was stronger. By comparison, NOD mice were only moderately susceptible to hTg-induced EAT. However, thyroiditis was more severe in DR3+ Ab(0)/NOD than in DR3- NOD mice, with no difference in proliferative response to hTg harbouring heterologous epitopes. The confirmed permissiveness of HLA-DR3 molecules on an NOD background for EAT induction by both mTg and hTg supports the importance of this class II gene implicated in some patient studies.

Pathogenic thyroglobulin peptides as model antigens: insights on the induction and maintenance of autoimmune thyroiditis

In recent years, the discovery of pathogenic thyroglobulin (Tg) peptides has given a new impetus to study, at the basic level, mechanisms of induction and immunoregulation of autoimmune thyroiditis. The genetic control of the immune response against defined Tg epitopes and the diversity of the T-cell receptor repertoire recruited for their recognition were among the first issues examined. Some of these epitopes contained hormonogenic sites, i.e. thyroxine residues, and thus offered an excellent opportunity to study how post-translational modifications such as iodination, can influence induction of thyroiditogenic cells. The delineation of pathogenic Tg determinants also enabled the search for "molecular mimics" i.e. peptides of microbial origin that may be involved in the pathogenesis of the disease. In addition, factors promoting the generation of pathogenic epitopes during Tg processing in antigen presenting cells could now be systematically investigated. This review summarizes recent findings in these areas.

Involvement of Epitope Mimicry in Potentiation But Not Initiation of Autoimmune Disease

We have examined whether the peptide (368–381) from the murine adenovirus type 1 E1B sequence, exhibiting a high degree of homology with the known pathogenic thyroglobulin (Tg) T cell epitope (2695–2706), can induce experimental autoimmune thyroiditis (EAT) in SJL/J mice. The viral peptide was a poor immunogen at the T or B cell level and did not elicit EAT either directly or by adoptive transfer assays. Surprisingly, however, the viral peptide was highly antigenic in vitro, activating a Tg2695–2706-specific T cell clone and reacting with serum IgG from mice primed with the Tg homologue. The viral peptide also induced strong recall responses in Tg2695–2706-primed lymph node cells, and subsequent adoptive transfer of these cells into naive mice led to development of highly significant EAT. These data demonstrate that nonimmunogenic viral peptides can act as agonists for preactivated autoreactive T cells and suggest that epitope mimicry may at times play a potentiating rather than a precipitating role in the pathogenesis of autoimmune disease.