Ajjan R A, Kemp E H, Waterman E A, Watson P F, Endo T, Onaya T, Weetman A P
Division of Clinical Sciences, Northern General Hospital, University of Sheffield, United Kingdom.
J Clin Endocrinol Metab. 2000 May;85(5):2020-7. doi: 10.1210/jcem.85.5.6526.
The sodium iodide symporter (NIS) is a novel autoantigen in autoimmune thyroid disease (ATD). A recent study has described the development of a bioassay for human (h) NIS antibody detection, but this will not detect antibodies that bind the symporter without modulating its activity. Therefore, the establishment of a binding assay is of importance to determine the overall prevalence of hNIS antibodies in ATD patients. An in vitro transcription and translation system was used to produce [35S]-labeled hNIS. The radiolabeled ligand reacted specifically in immunoprecipitation experiments with rabbit antiserum raised against a peptide fragment of hNIS. Subsequently, the reactivity of control and ATD sera to translated [35S]hNIS was determined using RIAs. A significant difference in the frequency of hNIS antibody-positive sera was found when patients with either Graves' disease (GD) or autoimmune hypothyroidism (AH) were compared with normal controls (P = 0.01 and P = 0.03, respectively). Of 49 GD and 29 AH sera tested, 11 (22%) and 7 (24%), respectively, were found to contain hNIS antibodies. Differences were also significant when the antibody-binding indices of the control group of sera were compared with those of both the GD and the AH patient sera (P < 0.0001 and P = 0.001, respectively). In contrast, sera from 10 patients with Addison's disease and 10 patients with vitiligo (without associated ATD) were all negative for antibody reactivity to the symporter. No differences were detected when the antibody binding indices of either the Addison's disease or the vitiligo sera were compared with those of the normal sera group (P = 0.9 and P = 0.6, respectively). Eight of the 11 (73%) GD and 3 of the 7 (43%) AH sera, which were positive for hNIS antibodies in the immunoprecipitation assay, were also found to inhibit iodide uptake in hNIS-transfected CHO-K1 cells, suggesting the existence of antibodies in some serum samples that bind to the symporter without modulating its function. Overall, a significant correlation was found between the iodide uptake inhibition and the binding assays for hNIS antibody detection (r = 0.49, P < 0.0001). In summary, we have developed a specific and quantitative assay for the detection of hNIS binding antibodies in sera of patients with ATD. This system offers the advantage of studying antibody reactivity against conformational epitopes and will be useful in understanding the role of NIS autoreactivity in the pathogenesis of ATD.
碘化钠同向转运体（NIS）是自身免疫性甲状腺疾病（ATD）中的一种新型自身抗原。最近的一项研究描述了一种用于检测人（h）NIS抗体的生物测定法的开发，但该方法无法检测到那些与转运体结合但不调节其活性的抗体。因此，建立一种结合测定法对于确定ATD患者中hNIS抗体的总体患病率至关重要。利用体外转录和翻译系统产生[35S]标记的hNIS。在免疫沉淀实验中，放射性标记的配体与针对hNIS肽片段产生的兔抗血清发生特异性反应。随后，使用放射免疫分析法（RIA）测定对照血清和ATD血清与翻译后的[35S]hNIS的反应性。当将格雷夫斯病（GD）或自身免疫性甲状腺功能减退症（AH）患者与正常对照进行比较时，发现hNIS抗体阳性血清的频率存在显著差异（分别为P = 0.01和P = 0.03）。在检测的49份GD血清和29份AH血清中，分别有11份（22%）和7份（24%）被发现含有hNIS抗体。当将血清对照组的抗体结合指数与GD和AH患者血清的抗体结合指数进行比较时，差异也很显著（分别为P < 0.0001和P = 0.001）。相比之下，10例艾迪生病患者和10例白癜风患者（无相关ATD）的血清对该转运体的抗体反应均为阴性。当将艾迪生病或白癜风血清的抗体结合指数与正常血清组的抗体结合指数进行比较时，未检测到差异（分别为P = 0.9和P = 0.6）。在免疫沉淀测定中hNIS抗体呈阳性的11份GD血清中的8份（73%）和7份AH血清中的3份（43%），也被发现能抑制hNIS转染的CHO-K1细胞中的碘摄取，这表明在一些血清样本中存在与转运体结合但不调节其功能的抗体。总体而言，发现碘摄取抑制与hNIS抗体检测的结合测定之间存在显著相关性（r = 0.49，P < 0.0001）。总之，我们开发了一种特异性和定量的测定法，用于检测ATD患者血清中的hNIS结合抗体。该系统具有研究针对构象表位的抗体反应性的优势，将有助于理解NIS自身反应性在ATD发病机制中的作用。
