Re-visiting autoimmunity to sodium-iodide symporter and pendrin in thyroid disease

Abstract

Objective: Iodide transport across thyrocytes constitutes a critical step for thyroid hormone biosynthesis, mediated mainly by the basolateral sodium-iodide-symporter (NIS) and the apical anion exchanger pendrin (PDS). Both transmembrane proteins have been described as autoantigens in thyroid disease, yet the reports on autoantibody (aAb) prevalence and diagnostic usefulness are conflicting. Reasons for the inconclusive findings may be small study groups and principle differences in the technologies used. Design: We decided to re-evaluate this important issue by establishing novel non-radioactive tests using full-length antigens and comparable protocols, and analysing a large cohort of thyroid patients (n=323) and control samples (n=400). Methods: NIS and PDS were recombinantly expressed as fusion protein with firefly luciferase (Luc). Stably transfected HEK293 cells were used as reproducible source of the autoantigens. Results: Recombinant NIS-Luc showed iodide transport activity, indicating successful expression and correct processing. Commercial antibodies yielded dose-dependent responses in the newly established assays. Reproducibility of assay signals from patient sera was verified with respect to linearity, stability and absence of matrix effects. Prevalence of PDS-aAb was similar in thyroid patients and controls (7.7% versus 5.0%). NIS-aAb were more prevalent in patients (7.7% versus 1.8%), especially in Graves’ Disease (12.3%). Neither NIS-aAb nor PDS-aAb concentrations were related to TPO-aAb or TSH-receptor-aAb concentrations, or to serum zinc or selenium status. Conclusions: Our data highlight a potential relevance of autoimmunity against NIS for thyroid disease, whereas an assessment of PDS-aAb in thyroid patients seems not to be of diagnostic value (yet).

Natural Autoimmunity to the Thyroid Hormone Monocarboxylate Transporters MCT8 and MCT10

“…Initially, strongly varying and particularly high prevalence has been reported in thyroid patients, partly due to the usage of small peptides as bait molecules in the aAb assays. Subsequent studies using full-length proteins either by radioactive ligand binding [46] or via detection of antigen-reporter fusion proteins [26] indicated a similar and moderate prevalence, and in a range compatible to what is reported in this manuscript for MCT8-aAb and MCT10-aAb, respectively. Longitudinal studies for elucidating a potential role of such aAb for thyroid disease incidence are consistently lacking, but it is not unlikely that transporter-targeting aAb to iodide or TH uptake are eliciting biological activity in human subjects.…”

Natural Autoimmunity to the Thyroid Hormone Monocarboxylate Transporters MCT8 and MCT10

“…Initially, strongly varying and particularly high prevalence has been reported in thyroid patients, partly due to the usage of small peptides as bait molecules in the aAb assays. Subsequent studies using full-length proteins either by radioactive ligand binding [39] or via detection of antigen-reporter fusion proteins [19] indicated a similar and moderate prevalence, and in a range compatible to what is reported in this manuscript for MCT8-aAb and MCT10-aAb, respectively. Longitudinal studies for elucidating a potential role of such aAb for thyroid disease incidence are consistently lacking, but it is not unlikely that transporter-targeting aAb to iodide or TH uptake are eliciting biological activity in human subjects.…”

“…The identification of MCT8-aAb and MCT10-ab is not very surprising, as there is an increasing number of well-characterized examples of clinically relevant aAb to endocrinerelevant membrane proteins. Besides the already mentioned TSH-receptor, also the thyroid transporters for iodide, i.e., the sodium-iodide symporter (NIS) and pendrin, have been described as potential autoantigens of the TH axis, and reliable test systems have been developed [19,39]. Initially, strongly varying and particularly high prevalence has been reported in thyroid patients, partly due to the usage of small peptides as bait molecules in the aAb assays.…”

“…The open reading frames encoding human MCT8 and human MCT10, respectively, were amplified by PCR and fused in frame to a firefly luciferase gene (Luc), essentially as described [18][19][20]. The resulting composite reading frame was inserted into the expression vector pIRESneo, generating the expression vectors pIRESneo-MCT8-Luc and pIRESneo-MCT10-Luc, respectively.…”

“…The suspension was cleared by centrifugation (2,000 g, 5 min, 4 °C), the supernatant was collected, stored at -80 C in aliquots, and thawed when needed for the measurements. Precipitation assays were established with the transporter fusion proteins, essentially as described previously [18][19][20].…”