Misharin Alexander V, Rapoport Basil, McLachlan Sandra M
Autoimmune Disease Unit, Cedars-Sinai Medical Center, Los Angeles, CA, USA.
Thyroid. 2009 May;19(5):503-9. doi: 10.1089/thy.2008.0420.
Vaccination with cDNA for the human thyrotropin receptor (TSHR) in a plasmid, without adjuvant, induces TSHR antibodies in C57BL/6 but rarely in BALB/c mice. This outcome could be due to a difference between "high" versus "low" antibody responder mouse strains. However, unlike their poor response to TSHR-DNA vaccination, BALB/c mice vaccinated with thyroid peroxidase (TPO)-cDNA readily develop antibodies to TPO. We hypothesized that insight into these conundrums would be provided by the following differences in central tolerance: (i) between two mouse strains (C57BL/6 versus BALB/c) for the TSHR; and (ii) between two thyroid autoantigens (TPO and the TSHR) in one mouse strain (BALB/c).
We studied autoantigen expression using real-time polymerase chain reaction to quantify mRNA transcripts for the TSHR, TPO, and thyroglobulin (Tg) in thymic tissue (as well as in thyroid) of young mice.
Our hypothesis was not confirmed. Intrathymic TSHR transcript expression was similar in BALB/c and C57BL/6 mice. Moreover, thymic mRNA transcripts for TSHR and TPO were comparable. Unlike the 10-fold differences for the autoantigens in thyroid tissue (Tg greater than TPO which, in turn was greater than the TSHR), intrathymic transcripts for TPO and the TSHR were similar, both being slightly lower than the level for Tg.
Central tolerance, assessed by measuring intrathymic transcripts of thyroid autoantigens, does not explain the different outcome of TSHR-DNA vaccination in BALB/c and C57BL/6 mice, or even susceptibility versus resistance to hyperthyroidism induced by TSHR-adenovirus. Instead, differences in MHC and TSHR T-cell epitopes likely contribute to TSHR antibody development (or not) following DNA plasmid immunization. The greater immunogenicity of TPO versus TSHR probably relates to the greater number of nonhomologous amino acids in the human and mouse TPO ectodomains (78 amino acids) than in the human and mouse TSHR ectodomains (58 amino acids). Overall, the autoantigens themselves, not central tolerance, control DNA plasmid-induced immunity to TPO and the TSHR.
用质粒中的人促甲状腺激素受体（TSHR）cDNA进行无佐剂疫苗接种，可在C57BL/6小鼠中诱导产生TSHR抗体，但在BALB/c小鼠中很少诱导产生。这种结果可能是由于“高”抗体应答小鼠品系与“低”抗体应答小鼠品系之间存在差异。然而，与它们对TSHR-DNA疫苗接种的不良反应不同，用甲状腺过氧化物酶（TPO）-cDNA接种的BALB/c小鼠很容易产生针对TPO的抗体。我们推测，通过以下中枢耐受方面的差异可以深入了解这些难题：（i）两种小鼠品系（C57BL/6与BALB/c）对TSHR的差异；（ii）一种小鼠品系（BALB/c）中两种甲状腺自身抗原（TPO和TSHR）之间的差异。
我们使用实时聚合酶链反应研究年轻小鼠胸腺组织（以及甲状腺）中TSHR、TPO和甲状腺球蛋白（Tg）的自身抗原表达，以定量mRNA转录本。
我们的假设未得到证实。BALB/c和C57BL/6小鼠胸腺内TSHR转录本表达相似。此外，TSHR和TPO的胸腺mRNA转录本相当。与甲状腺组织中自身抗原10倍的差异（Tg大于TPO，而TPO又大于TSHR）不同，TPO和TSHR的胸腺内转录本相似，均略低于Tg的水平。
通过测量甲状腺自身抗原的胸腺内转录本来评估的中枢耐受，无法解释BALB/c和C57BL/6小鼠中TSHR-DNA疫苗接种的不同结果，甚至无法解释对TSHR-腺病毒诱导的甲状腺功能亢进的易感性与抗性差异。相反，MHC和TSHR T细胞表位的差异可能导致DNA质粒免疫后TSHR抗体的产生（或不产生）。TPO相对于TSHR更高的免疫原性可能与人和小鼠TPO胞外域（78个氨基酸）中比人和小鼠TSHR胞外域（58个氨基酸）更多的非同义氨基酸有关。总体而言，自身抗原本身而非中枢耐受控制着DNA质粒诱导的对TPO和TSHR的免疫。
