Abstract
Transgenic mice with the human thyrotropin-receptor (TSHR) A-subunit targeted to the thyroid are tolerant of the transgene. In transgenics that express low A-subunit levels (Lo-expressors), regulatory T cell (Treg) depletion using anti-CD25 before immunization with adenovirus encoding the A-subunit (A-sub-Ad) breaks tolerance, inducing extensive thyroid lymphocytic infiltration, thyroid damage and antibody spreading to other thyroid proteins. In contrast, no thyroiditis develops in Hi-expressor transgenics or wild-type mice. Our present goal was to determine if thyroiditis could be induced in Hi-expressor transgenics using a more potent immunization protocol: Treg depletion, priming with Complete Freund's Adjuvant (CFA) + A-subunit protein and further Treg depletions before two boosts with A-sub-Ad. As controls, anti-CD25 treated Hi- and Lo-expressors and wild-type mice were primed with CFA+ mouse thyroglobulin (Tg) or CFA alone before A-sub-Ad boosting. Thyroiditis developed after CFA+A-subunit protein or Tg and A-sub-Ad boosting in Lo-expressor transgenics but Hi- expressors (and wild-type mice) were resistant to thyroiditis induction. Importantly, in Lo-expressors, thyroiditis was associated with the development of antibodies to the mouse TSHR downstream of the A-subunit. Unexpectedly, we observed that the effect of bacterial products on the immune system is a “double-edged sword”. On the one hand, priming with CFA (mycobacteria emulsified in oil) plus A-subunit protein broke tolerance to the A-subunit in Hi-expressor transgenics leading to high TSHR antibody levels. On the other hand, prior treatment with CFA in the absence of A-subunit protein inhibited responses to subsequent immunization with A-sub-Ad. Consequently, adjuvant activity arising in vivo after bacterial infections combined with a protein autoantigen can break self-tolerance but in the absence of the autoantigen, adjuvant activity can inhibit the induction of immunity to autoantigens (like the TSHR) displaying strong self-tolerance.
Highlights
Transgenic mice with the A-subunit of the human thyrotropin receptor (TSHR) targeted to the thyroid gland exhibit tolerance to the transgene
We found that massive thyroiditis, associated with thyroid damage and thyroid antibody spreading to Tg and thyroid peroxidase (TPO), was induced by Treg depletion using anti-CD25 before immunization with TSHR adenovirus in transgenic mice expressing low, but not high, levels of the human TSHR A-subunit in the thymus and thyroid [2,4]
The goal of the present study was to determine if a potent immunization protocol, namely complete Freund’s Adjuvant (CFA)+A-subunit protein, followed by boosting with Asub-adenovirus in Treg depleted animals could break tolerance and induce thyroiditis in Hi-expressor transgenics
Summary
Transgenic mice with the A-subunit of the human thyrotropin receptor (TSHR) targeted to the thyroid gland exhibit tolerance to the transgene. Unlike wild type littermates, the transgenics do not respond to immunization with a low dose of adenovirus encoding the autoantigen, the human TSHR A-subunit [1]. Two transgenic lines express different amounts of TSHR A-subunit in the thyroid gland and the thymus [2,3]. Because of different expression levels in the thymus, these mouse lines have different levels of self-tolerance to the human A-subunit. Transgenic mice that express high levels of the transgene (Hi-expressors) generate little or no TSHR antibody in response to high dose A-subunit adenovirus immunization, even if pre-treated with anti-CD25 to deplete regulatory T cells (Treg)[2,3]. TSHR antibodies induced using adjuvant are non-stimulatory and do not induce hyperthyroidism
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