Association Between Autoantibodies Against Thyroid Stimulating Hormone Receptor and Thyroid Diseases.

AIM: The aim of this study is to determine the relationship between TRAb and different diseases. The highest percentage of increased TRAb levels can be found at patients with Graves'™ diseases.
MATERIAL AND METHODS: Study was performed in 70 patients, grouped in three gr oups, and 14 persons who based on the clinical status and the levels of thyroid hormones do not ha ve any thyroid disease. The TRAb levels has been determined in patients with Graves'™ disease (N=40) , Hashimoto'™s disease (N=15), Plummer'™s disease (N=15) and the control group (N=14).
RESULTS: The highest mean TRAb levels exist in patients with Graves'™ disease. There exists a positive correlation between TRAb levels and T3, and T4, while there is no correlat ion between TSH and TRAb levels in patients with Graves'™ disease,. On the other hand, the correlati on between TRAb and T3 and T4 in patients with Hashimoto'™s diseases and Plummers disease was shown to be positive, but of a low levels.

1. INTRODUCTION

Thyroid autoimmune diseases – AITD – is a group of diseases with different clinical and laboratory manifestations (1, 2), with the possibility of progression based on another clinical disorder (3). while it is well known that Graves’ disease and chronic autoimmune thyroiditis – Hashimoto’s thyroiditis are autoimmune diseases, the association between autoimmune process and development of toxic nodular goiter (Plummer disease) still remains unclear (4).

Autoimmune thyroid diseases are characterized by spontaneous production of autoantibodies against thyroid antigens (5). Autoantibodies against the following antigenic molecules of thyroid gland can be detected in the serum of patients with AITD: thyrotropin receptor (TSH-R), thyroglobulin (Tg), thyroperoxidase (TPO), thyrostimulating hormone itself, etc. Autoantibodies against TSH receptor – TRAb, thyroglobulin – TgAb and autoantibodies against thyroperoxidase – TPOAb, are of paramount clinical importance for diagnosis and prognosis of thyroid diseases (6).

The main protein that controls the function of thyroid gland and which is in fact the main auto antigen, is the receptor for TSH. There are three categories of autoantibodies against the receptor for TSH. The first category contains thyroid-stimulating antibodies (TSAb) that have analogous functions to TSH and work by stimulating the adenyl cyclase. The second category contains autoantibodies that inhibit binding of TSH in the membrane of thyrocytes (TBII). The third category contains thyroid-blocking antibodies (TBAb) that block interaction of TSH to TSHR. The first and second categories cause hyperthyroidism in Graves’ disease, while the third category of autoantibodies of TRAb causes hypothyroidism in patients with atrophic thyroiditis and in some Graves’ disease patients.

Determining the levels of TRAb is of clinical value for diagnosing of Graves’ disease, evaluation of prognosis, and for predicting neonatal hyperthyroidism. This also helps in diagnosis of euthyroid Graves’ disease patients.

2. OBJECTIVE

The aim of this study is to determine the relationship between TRAb and different diseases. For the purpose of this study, the following has been researched: the percentage of increased TRAb levels in the above mentioned diseases, mean levels of these autoantibodies, and the correlation between the TRAb levels and T3, T4 and TSH.

3. MATERIAL AND METHODS

In this study the patients sera with different thyroid diseases has been utilized. Study was performed in 70 patients, grouped in three groups, and 14 persons who based on the clinical status and the levels of thyroid hormones do not have any thyroid disease. The TRAb levels has been determined in patients with Graves’ disease (N=40), Hashimoto’s disease (N=15), Plummer’s disease (N=15) and the control group (N=14).

Included patients in this study did not have any previous therapeutic treatment and were diagnosed in the Department of Endocrinology whereas laboratory measurements were done in Department of Physiology University Clinical Center, Prishtina, Kosovo. This research was approved by Faculty of Medicine, Teaching-Science Council, and was conform to the provisions of the Declaration of Helsinki (paragraph 11, 13,15, 16, 20). Informed written consent was obtained from all subjects before inclusion in the study.

The diagnosis of patients was based on clinical status, laboratory data – TSH, T3 and T4 levels, as well ultrasonographic and histopathologic findings. Basic precondition for inclusion of patients in the study was disease diagnosis based on clinical status and, at least, two of above mentioned parameters. For serum isolation the blood was taken from vena mediana cubiti. The isolated sera were kept in refrigerator at -200C until the determination of the levels of autoantibodies was done.

The radio receptor assay – RRA was used in order to determine the levels of autoantibodies against TSHR. For quantitative determination of autoantibodies against TSHR (TRAb) the DYNOtest TRAK human reagent kit, article nr: 101.1, produced by B.R.A.H.M.S. Diagnostica GmbH was utilized.

The radioactivity of samples was measured using DPC-type gamma counter, while the result calculation was done using GMS software application. Using this method, values < 1IU/L are considered negative, while values > 1 IU/L are considered positive.

4. RESULTS

In Table 1 we presented the percentage of increased TRAb levels in patients, groped in two groups (group with “normal TRAb values” and group with “increased TRAb values”), according to diseases and control group.

Table 1

The percentage of incresed TRAb levels and mean TRAb levels (UI/L) by diseases. Data are shown as mean ± SD. Statistical analyses were performed with student t-test, p<0.05. Significant statistical difference in the percentage of cases with increased TRAb levels, compared to control group, was only observed at patients with Graves’ disease (p < 0.002), while the percentage of increased TRAb levels in patients with Hashimoto’s disease and Plummer’s disease, compared to the control group did not show any statistically significant difference (p>0,3 respectively p > 0.5). The mean TRAb levels are significantly greater in Graves’ disease vs. Hashimoto’s thyroiditis and control group (p<0.0001).

In the higher percentage, the increased TRAb levels was shown to be in the group of patients with Graves’ disease (34/40,85%), while in those with Hashimotos’ disease and Plummer’s disease, the increased levels was at 40% (6/15), namely 33.33% (5/15) of cases. In the control group, this levels was increased only in 21.43% (3/14).

In patients with thyroid diseases, a significant statistical difference in the percentage of cases with increased TRAb levels, compared to control group, was only observed at patients with Graves’ disease (p < 0.002), while the percentage of increased TRAb levels in patients with Hashimoto’s disease and Plummer’s disease, compared to the control group did not show any statistically significant difference (p>0,3 respectively ρ > 0.5).

In the Table 1, it can be observed that higher TRAb levels are found in the group of patients with Graves’ disease. The mean TRAb levels in patients with Graves’ disease has shown significant statistical difference, compared to mean TRAb levels in patients with Hashimoto’s disease, patients with Plummer’s disease, and control group. The mean TRAb levels in patients with Hashimoto’s disease, has shown significant difference compared to mean levels of these autoantibodies in patients with Plummer’s disease and control group. Negligible statistical difference was found between TRAb mean levels in patients with Plummer’s diseases and control group.

The correlation between TRAb levels and T3, T4 and TSH hormones was specifically analyzed. In patients with Graves’ disease, a positive medium correlation (r = 0.62, t=4.87, df=38, p=0.00002), with regression line: y=0.0363x+3.0275, between levels of T3 and TRAb was found. Another positive correlation was also found between levels of T4 and TRAb (r = 0.50, t=3.61, df=38, p=0.001), with regression line: y=1.7791x+168.66 (Diagram 1). A low negative correlation was found between levels of TSH and TRAb in patients with Graves’ disease (r = -0.21, t=1.34, df=38, p=0.189), with regression line: y = -0.0044X+0.7108. (Diagram 1)

Diagram 1

Correlation between levels of T4 and TRAb in patients with Graves’ disease Positive correlation was also found between levels of T4 and TRAb (r = 0.50, t=3.61, df=38, p=0.001), with regression line: y=1.7791x+168.66

A low positive correlation between levels of T3 and TRAb was found in patients with Hashimoto’s disease. In these patients, also, the correlation between T4 and TSH and TRAb levels was negative.

In patients with Plummer’s disease, a low positive correlation between T3 and TRAb levels was found. A negative correlation between T4 and TRAb levels was observed, but of a low levels. Finally, a low positive correlation was also observed between TSH and TRAb levels.

5. DISCUSSION

Different authors found different percentage of cases with increased TRAb levels depending on the method they used. On the other side, great variations are found in patients with Graves’ disease living in Great Britain, depending on the region, in a structure of 35% in Prinston until 92% in Suthampton (13). Also, there is a wide range of occurrence in the percentage of patients with Graves’ disease, which is a consequence of their clinical status, considering that a considerable number of them at the same time produce thyrostimulating and thyroblocking autoantibodies (7,14,15).

According to Hasse-Lazar (16), the increased TRAb autoantibodies levels was observed in 94,1% of patients with Graves diseases (mean value 52 U/L), 12.5% at those with Hashimoto’s diseases (mean levels value 4,1 U/L), 25% of patients with Plummer’s disease (mean levels value 4,1 U/L), while an increased levels of these autoantibodies was observed at 4,8% of control group (mean levels value 1,7 U/L). Giovanella et.al (12) observed 89,1% (41/46) of cases with increased TRAb levels at patients with Graves’ disease.

Zophel et.al (8) concluded that increased TRAb levels was present in 86.7% (52/60) of patients with Grave’s disease that were in relapse period after therapeutic treatment. On the other hand, Sergio (10) observed increased TRAb levels at 84,5% (62/73) of patients with Graves’ disease, while at no one in the control group (0/60).

According to the above, the results presented in our study with regards to increased TRAb levels in patients with Graves’ disease conform to the results of some authors (8,10,12), while the percentage of increased levels of these autoantibodies in patients with Hashimoto’s disease, conform to the results of Trbojevic (9), considering that almost all patients in this study were with TSH value above 5 U/L. On the other hand, it is known that increased levels of TSH at patients with Hashimoto’s disease leads to an increase in expression of HLA DR antigens in thyrocites and expression of thyroid antigens, which causes the increase in TRAb levels (6).

With regards to the percentage of increased TRAb levels in patients with Plummer’s disease and control group, this study shows higher levels compared to other authors, but with an mean, almost undetectable levels, which is a consequence of the sample size.

Rieu M in his study (11) shows that hormonal status modulates the appearance of thyroid autoimmunity, by concluding that there exists a significant correlation between some hormonal parameters and TRAb (T3, r = 0.42, P < 0.001; T4, r = 0.48, p < 0.001) at patients with Graves’ diseases, something that was also shown in this study.

6. CONCLUSIONS

The highest percentage of increased TRAb levels can be found at patients with Graves’ diseases. The highest mean TRAb levels exist in patients with Graves’ disease. There exists a positive correlation between TRAb levels and T3, and T4, while there is no correlation between TSH and TRAb levels in patients with Graves’ disease,. On the other hand, the correlation between TRAb and T3 and T4 in patients with Hashimoto’s diseases and Plummers disease was shown to be positive, but of a low levels.