Role of MHC class II antigen expression in thyroid autoimmunity

Pathogenesis of Hyperthyroidism

Hyperthyroidism is a form of thyrotoxicosis in which there is excess thyroid hormone synthesis and secretion. Multiple etiologies can lead to a common clinical state of "thyrotoxicosis," which is a consequence of the high thyroid hormone levels and their action on different tissues of the body. The most common cause of thyrotoxicosis is Graves' disease, an autoimmune disorder in which stimulating thyrotropin receptor antibodies bind to thyroid stimulating hormone (TSH) receptors on thyroid cells and cause overproduction of thyroid hormones. Other etiologies include: forms of thyroiditis in which inflammation causes release of preformed hormone, following thyroid gland insult that is autoimmune, infectious, mechanical or medication induced; secretion of human chorionic gonadotropin in the setting of transient gestational thyrotoxicosis and trophoblastic tumors; pituitary thyrotropin release, and exposure to extra-thyroidal sources of thyroid hormone that may be endogenous or exogenous. © 2017 American Physiological Society. Compr Physiol 7:67-79, 2017.

Induction of thyroid-stimulating hormone receptor autoimmunity in hamsters

Female Chinese hamsters (n = 10) were immunized with Chinese hamster ovary (CHO) cells that expressed the human TSH receptor (TSHR) to generate a model of Graves' disease. TSHR-autoantibodies (TSHR-Ab) were determined by CHO-TSHR. Two hamsters with stimulating TSHR-Ab showed thyrocyte hypertrophy associated with a focal lymphocytic infiltration. CHO-TSHR were then stimulated with interferon gamma to enhance major histocompatibility complex class II expression. However, after immunization no stimulating TSHR-Ab were detected, but blocking TSHR-Ab were found in three of five animals. The thyroid glands from these hamsters showed marked thinning of thyroid epithelial cells, indicative of early thyroid atrophy consistent with a TSHR blocking antibody, but no lymphocytic infiltration. Lastly, female Armenian hamsters were immunized with an adenovirus construct incorporating wild-type TSHR. High titers of TSHR-Ab were induced effectively, but the thyroid hypertrophy observed was not associated with a lymphocyte infiltration. In summary, we demonstrated that the hamster could serve as a model of TSHR autoimmunity and that an adenoviral vector produced higher levels of TSHR-Ab than more conventional immunization with cells. The data also indicated that the intrathyroidal cellular immunity in this model was not related to TSHR-Ab formation and was an independent reflection of the T-cell immune response to TSHR antigen.

A C/T single-nucleotide polymorphism in the region of the CD40 gene is associated with Graves' disease

Graves' disease (GD) develops as a result of an interaction between susceptibility genes and environmental factors. We have previously mapped a susceptibility locus for GD on chromosome 20q11 (GD-2), which has recently been independently replicated. Among the genes mapped to 20q11 was the CD40 gene, an important costimulatory molecule and a good positional candidate gene for GD. We investigated whether the CD40 gene was the GD susceptibility gene on 20q11. Linkage analysis in a subset of Caucasian families showed a maximum multipoint logarithm of odds (LOD) score of 3.3 at the CD40 locus. We then sequenced all 9 exons of the CD40 gene in 8 probands and 10 controls and identified a new C/T single-nucleotide polymorphism (SNP) in the Kozak sequence of the CD40 gene at position -1. Case control association analysis of the CD40 C/T(-1) SNP in 154 Caucasian patients with GD and 118 Caucasian controls showed an association between the CC genotype and GD (p = 0.048, relative risk [RR] = 1.6). Furthermore, the association was stronger when only the probands from the linked families (n = 20) were used (p = 0.009, RR = 4.8). Transmission disequilibrium test (TDT) analysis also showed preferential transmission of the C allele of the CD40 C/T(-1) SNP to affected individuals (p = 0.02). In conclusion, our results suggested that the CD40 gene was a new susceptibility gene for GD within certain families because it was both linked and associated with GD.