Francesco Latrofa

Disappearance of humoral thyroid autoimmunity after complete removal of thyroid antigens.

RiassuntoLe malattie autoimmuni della tiroide sono caratterizzate dalla presenza di anticorpi diretti contro la tireoperossidasi (TPO), la tireoglobulina (Tg) e il recettore per l’ormone tireotropo (TSH-R). Questo studio ha valutato se la rimozione completa degli antigeni tiroidei fosse in grado di indurre la scomparsa dei segni di autoimmunità tiroidea circolante. Lo studio è basato su una revisione retrospettiva delle cartelle cliniche di pazienti che erano stati seguiti e trattati secondo un protocollo standard. Sono stati studiati 182 pazienti affetti da tumore differenziato della tiroide i quali, per la coesistenza di una tiroidite cronica autoimmune, di un morbo di Basedow o di una tiroidite focale autoimmune, risultavano positivi per anticorpi anti-TPO (TPOAb), anti-Tg (TgAb) o anti-TSH-R (TRAb). Dei 182 soggetti, 151 erano di sesso femminile e 31 di sesso maschile; l’età media era di 39,7±13,7 anni, con un range da 6 a 81 anni. Tutti i pazienti sono stati sottoposti a tiroidectomia totale e a trattamento con iodio radioattivo allo scopo di ablare il tessuto tiroideo residuo o metastatico. Il follow-up è stato effettuato mediante scintigrafie corporee totali con radioiodio e dosaggio della Tg circolante. La media del follow-up era di 10,1±4,1 anni, con un range di 4–20 anni. A seguito del trattamento con tiroidectomia totale e iodio radioattivo, si è verificata la scomparsa dei TgAb, TPOAb e TRAb. La mediana di scomparsa è stata di 6,3 anni per iTPOAb e di 3,0 anni per i TgAb. La scomparsa del tessuto tiroideo e quella degli anticorpi antitiroide erano correlate in modo statisticamente significativo. La persistenza di TPOAb e TgAb non veniva influenzata dal sesso, dall’età e dalla concomitanza della tiroidite autoimmune o del morbo di Basedow.

The thyrotropin receptor autoantigen in Graves disease is the culprit as well as the victim

Graves disease, a common organ-specific autoimmune disease affecting humans, differs from all other autoimmune diseases in being associated with target organ hyperfunction rather than organ damage. Clinical thyrotoxicosis is directly caused by autoantibodies that activate the thyrotropin receptor (TSHR). The etiology of Graves disease is multifactorial, with nongenetic factors playing an important role. Of the latter, there is the intriguing possibility that the molecular structure of the target antigen contributes to the development of thyroid-stimulatory autoantibodies (TSAbs). Among the glycoprotein hormone receptors, only the TSHR undergoes intramolecular cleavage into disulfide-linked subunits with consequent shedding of some of the extracellular, autoantibody-binding A subunits. Functional autoantibodies do not arise to the noncleaving glycoprotein hormone receptors. Recently, TSAbs were found to preferentially recognize shed, rather than attached, A subunits. Here we use a new adenovirus-mediated animal model of Graves disease to show that goiter and hyperthyroidism occur to a much greater extent when the adenovirus expresses the free A subunit as opposed to a genetically modified TSHR that cleaves minimally into subunits. These data show that shed A subunits induce or amplify the immune response leading to hyperthyroidism and provide new insight into the etiology of Graves disease.

Thyroid-stimulating autoantibodies in Graves disease preferentially recognize the free A subunit, not the thyrotropin holoreceptor.

Graves disease is directly caused by thyroid-stimulating autoantibodies (TSAbs) that activate the thyrotropin receptor (TSHR). We observed upon flow cytometry using intact cells that a mouse mAb (3BD10) recognized the TSHR ectodomain with a glycosidylphosphatidylinositol (ECD-GPI) anchor approximately tenfold better than the same ectodomain on the wild-type TSHR, despite the far higher level of expression of the latter. The 3BD10 epitope contains the N-terminal cysteine cluster critical for TSAb action. Consequently, we hypothesized and confirmed that TSAb (but not thyrotropin-blocking autoantibodies [TBAbs]) also poorly recognize the wild-type TSHR relative to the ECD-GPI. Despite poor recognition by TSAb of the holoreceptor, soluble TSHR A subunits (known to be shed from surface TSHR) fully neutralized autoantibody-binding activity. These data indicate that the epitope(s) for TSAbs, but not for TBAbs, are partially sterically hindered on the holoreceptor by the plasma membrane, the serpentine region of the TSHR, or by TSHR dimerization. However, the TSAb epitope on the soluble A subunit is freely accessible. This observation, as well as other evidence, supports the concept that A subunit shedding either initiates or amplifies the autoimmune response to the TSHR, thereby causing Graves disease in genetically susceptible individuals.

Hashimoto's thyroiditis is associated with papillary thyroid carcinoma: role of TSH and of treatment with l-thyroxine

The possible association between Hashimoto’s thyroiditis (HT) and papillary thyroid carcinoma (PTC) is a still debated issue. We analyzed the frequency of PTC, TSH levels and thyroid autoantibodies (TAb) in 13 738 patients (9824 untreated and 3914 under L-thyroxine, L-T4). Patients with nodular-HT (nZ1593) had high titer of TAb and/or hypothyroidism. Patients with nodular goiter (NG) were subdivided in TAbKNG (nZ8812) with undetectable TAb and TAbCNG (nZ3395) with positive TAb. Among untreated patients, those with nodular-HT showed higher frequency of PTC (9.4%) compared with both TAbKNG (6.4%; PZ0.002) and TAbCNG (6.5%; PZ0.009) and presented also higher serum TSH (median 1.30 vs 0.71 mU/ml, P!0.001 and 0.70 mU/ml, P!0.001 respectively). Independently of clinical diagnosis, patients with high titer of TAb showed a higher frequency of PTC (9.3%) compared to patients with low titer (6.8%, P!0.001) or negative TAb (6.3%, P!0.001) and presented also higher serum TSH (median 1.16 vs 0.75 mU/ml, P!0.001 and 0.72 mU/ml, P!0.001 respectively). PTC frequency was strongly related with serum TSH (odds ratio (OR)Z1.111), slightly related with anti-thyroglobulin antibodies (ORZ1.001), and unrelated with anti-thyroperoxidase antibodies. In the L-T4-treated group, when only patients with serum TSH levels below the median value (0.90 mU/ml) were considered, no significant difference in PTC frequency was found between nodular-HT, TAbKNG and TAbCNG. In conclusion, the frequency of PTC is significantly higher in nodular-HT than in NG and is associated with increased levels of serum TSH. Treatment with L-T4reduces TSH levels and decreases the occurrence of clinically detectable PTC. Endocrine-Related Cancer (2011) 18 429‐437

Clinical features of thyroid autoimmunity are associated with thyroiditis on histology and are not predictive of malignancy in 570 patients with indeterminate nodules on cytology who had a thyroidectomy

Background  The relationship between thyroid autoimmunity and cancer is still uncertain.

Thyroglobulin Autoantibodies in Patients with Papillary Thyroid Carcinoma: Comparison of Different Assays and Evaluation of Causes of Discrepancies

CONTEXT Thyroglobulin autoantibodies (TgAb) have been proposed as a surrogate marker of thyroglobulin in the follow-up of differentiated thyroid carcinoma. Commercially available TgAb assays are often discordant. We investigated the causes of discrepancy. DESIGN TgAb were measured by three noncompetitive immunometric assays and three competitive RIA in 72 patients with papillary thyroid carcinoma and associated lymphocytic thyroiditis (PTC-T), 105 with papillary thyroid carcinoma and no lymphocytic thyroiditis (PTC), 160 with Hashimotos thyroiditis, and in 150 normal subjects. The results of the six assays were correlated. TgAb epitope pattern, evaluated by inhibition of serum TgAb binding to thyroglobulin by TgAb-Fab regions A, B, C, and D, were compared in sera which were positive in all six assays (concordant sera) and positive in only one to five assays (discordant sera) were compared. TgAb International Reference Preparation (IRP) was measured in 2007 and 2009. RESULTS The correlations of the six assays ranged from -0.01 to 0.93 and were higher in PTC-T and Hashimotos thyroiditis than in PTC and normal subjects. Two uncorrelated components, one including the three immunometric assays, the other the three RIA, explained 40 and 37% of the total variance of the results of the six assays. The levels of inhibition were higher in concordant sera than in discordant sera by TgAb-Fab region B (27.0%, 21.2-34.0 vs. 6.0%, and 2.7-12.7%) and region C (30.5%, 21.3-37.7 vs. 4.0%, and 1.0-6.5%); thus, the epitope pattern was more homogeneous in concordant sera than in discordant sera. TgAb IRP ranged from 157 to 1088 (expected 1000) IU/ml in 2009; results in 2007 were similar in all but two assays. CONCLUSIONS TgAb assays are highly discordant. Discrepancy is lower when comparing assays with similar methodology. Results of TgAb from PTC-T are more concordant than those from PTC because their epitope pattern is more restricted. The internal standardization of TgAb is generally, but not completely, satisfactory.

The large majority of 1520 patients with indeterminate thyroid nodule at cytology have a favorable outcome, and a clinical risk score has a high negative predictive value for a more cumbersome cancer disease.

CONTEXT Clinical management of patients with thyroid nodules indeterminate at fine-needle aspiration (FNA) cytology is still unsettled. OBJECTIVE Our objective was to establish the clinical outcome of patients with thyroid nodules indeterminate at cytology and to identify the features associated with malignancy. DESIGN AND PATIENTS This was a retrospective evaluation of 1520 consecutive patients with indeterminate cytology among 100 065 patients who underwent FNA between January 2000 and December 2010. RESULTS Of 1520 patients, 371 (24.4 %) had thyroid cancer at histology, the follicular variant of papillary cancer being the most frequent histotype, and 342 patients with cancer were free of disease after thyroidectomy and (131)I remnant ablation, whereas 29 needed further treatment because of persistent disease. Among them, only 12 had persistence of disease at the end of follow-up. Atypias at cytology (P = .001), blurred nodule margins (P = .005), and spot microcalcifications (P = .003) at thyroid ultrasound (US) were significantly associated with malignancy. A clinical score including cytology and US characteristics was calculated; the lowest value showed a high negative predictive value (83.9%) for the presence of malignancy and even higher (99.5%) for the presence of a more cumbersome cancer disease, and only 4 of the 29 patients who needed further treatment were included in the group with the lowest risk score. CONCLUSIONS Patients with Thy 3 cytology and histology of thyroid cancer had an overall good prognosis. A clinical risk score including the results of cytology and US features is helpful in the management of patients with indeterminate thyroid nodules.

Iodine Contributes to Thyroid Autoimmunity in Humans by Unmasking a Cryptic Epitope on Thyroglobulin

CONTEXT The mechanisms linking thyroid autoimmunity and iodine use in humans are unknown. OBJECTIVE Our aim was to correlate iodine intake, thyroid autoimmunity, and recognition of thyroglobulin (Tg) epitopes after implementation of iodine prophylaxis. SETTING The general community living in an Italian village was evaluated. MAIN OUTCOME MEASURES Thyroglobulin autoantibodies (TgAb), thyroperoxidase autoantibodies (TPOAb), and urinary iodine excretion were assessed in 906 iodized salt users (IS-users) and 389 nonusers (IS-nonusers). Ultrasound (US) was performed to identify thyroid hypoechogenicity, suggestive of Hashimoto thyroiditis (HT). TgAb epitope pattern in 16 IS-users and 17 IS-nonusers was evaluated by an inhibition binding assay to Tg, using human monoclonal TgAb-Fab directed to A, B, C, and D epitopes on Tg. RESULTS Median urinary iodine excretion was slightly higher in IS-users than in IS-nonusers (112.0 μg/L vs 86.5 μg/L; P < .01). TgAb, and not TPOAb, was more frequent in IS-users (18.9% vs 13.6%, P = .02). HT-US was found in 87 subjects, among whom both positive TgAb (58.4% vs 31.8%, P = .03) and TPOAb (61.5% vs 45.4%. P = .04) were more frequent in IS-users. In this group significantly higher serum levels of TgAb (median 108 U/mL vs 30 U/mL; P = .02), but not of TPOAb, were present. Iodized salt use had no effect on the 1208 non HT-US subjects. TgAb directed to the epitope B of Tg were more frequent in IS-users than in IS-nonusers (27.5% vs 3.0%, P = .047). CONCLUSIONS Iodine-induced thyroid autoimmunity is related to TgAb and the unmasking of a cryptic epitope on Tg contributes to this relationship in humans.

An update on the medical treatment of Graves’ hyperthyroidism

Medical treatment of Graves’ hyperthyroidism is based on the use of thionamides; namely, methimazole and propylthiouracil. In the past, methimazole was preferred by European endocrinologists, whereas propylthiouracil was the first choice for the majority of their North American colleagues. However, because of the recent definition of a better side-effect profile, methimazole is nowadays the first choice world while. Although thionamides are quite effective for the short-term control of Graves’ hyperthyroidism, a relatively high proportion of patients relapses after thionamide withdrawal. Other possible medical treatments, include iodine and compounds containing iodine, perchlorate, lithium (as an adjuvant in patients undergoing radioiodine therapy), β-adrenergic antagonists, glucocorticoids, and some new molecules still under investigation. Management of Graves’ hyperthyroidism using thionamides as well as the other available medical treatments is here reviewed in detail, with a special mention of situations such as pregnancy and lactation, as well as neonatal and fetal thyrotoxicosis.

Characterization of thyroglobulin epitopes in Sardinian adults and juveniles with Hashimoto's thyroiditis: evidence against a major effect of age and genetic background on B-cell epitopes.

Background  Using recombinant human monoclonal thyroglobulin antibodies expressed as Fab molecules (TgAb‐Fab), we have recently confirmed the restriction of Tg epitopes in Hashimoto’s thyroiditis (HT).