Sensitive assay to detect thyroid stimulating antibody (TSAb) in the presence of thyroid stimulation blocking antibody (TSBAb) in serum

Elevated follicular helper T cells and expression of IL-21 in thyroid tissues are involved in the pathogenesis of Graves' disease

The follicular helper T cell (Tfh) and IL-21 have been shown to play an important role in many autoimmune diseases. However, less is known about their role in Graves' disease (GD). This study aimed to investigate the expression of Tfhs and related factors (IL-21, IL-21R, CXCR5, and CXCL13) in GD thyroid tissues and to explore the effect of IL-21 on thyroid follicular cells (TFCs). The expression of Tfh-related factors in GD and normal thyroid tissues was validated using immunohistochemistry, real-time polymerase chain reaction and Western blotting. Confocal microscopy confirmed the presence of Tfh and IL-21R on CD4(+)T-/CD19(+)B cell in GD thyroid tissues. Furthermore, the effect of IL-21 on cAMP production in TFCs upon thyroid-stimulating antibody (TSAb) stimulation was also examined by an in vitro bioassay. The increased expression of Tfh-related factors was observed in GD thyroid tissues compared to control subjects. Confocal microscopy further confirmed the presence of Tfhs and the expression of IL-21R on CD4(+)T cells and CD19(+)B cells in GD thyroid tissues. Moreover, the expression of IL-21mRNA in GD thyroid tissues was correlated with the levels of thyroid autoantibodies. Additionally, IL-21 could indirectly promote cAMP production upon TSAb stimulation in TFCs when cooperating with lymphocytes, and GD TFCs were more sensitive to IL-21 stimulation than normal TFCs. There is increased expression of Tfhs and related factors (IL-21, IL-21R, CXCR5, and CXCL13) in GD thyroid tissues, and the expression of IL-21mRNA in GD thyroid tissues was found to correlate with the serum levels of thyroid autoantibodies and thyroid hormones. Moreover, IL-21 could indirectly enhance the biological activity of TFCs upon TSAb stimulation when cooperating with lymphocytes in vitro, particularly in GD TFCs, suggesting that Tfh and IL-21 might be involved in the pathogenesis of GD.

Interleukin-21 is associated with disease activity in patients with Graves' disease

Graves' disease (GD) is a common autoimmune disease mainly caused by thyroid-stimulating antibodies (TSAbs). Interleukin 21 (IL-21) has recently been reported to play a vital role in the production of pathogenic autoantibodies in several autoimmune diseases, but less is known about GD. This study aimed to investigate the serum levels of IL-21 in GD patients and to explore their association with disease activity. We performed a case-control association study of 152 patients with GD and 32 healthy controls. All patients were further classified into three subgroups: the GD-untreated group (n = 70), the GD-recurrence group (n = 41), and the GD-remission group (n = 41). Serum IL-21 levels were assayed with ELISA. TSAb activity was measured by an in vitro bioassay. Changes in serum IL-21 were also observed in 12 GD patients before and after treatment. Additionally, correlations among the serum IL-21 and free triiodothyronine (FT3), free thyroxine (FT4), thyrotropin (TSH), thyroperoxidase antibodies (TPOAb), thyroglobulin antibodies (TGAb), thyrotropin receptor antibody (TRAb), and TSAb were also analyzed. The serum IL-21 levels in all GD patients were significantly higher than those in the control group (P < 0.001), and specifically, both the GD-untreated and GD-recurrence groups had elevated serum IL-21 compared to the control group (P < 0.001). Moreover, serum IL-21 in newly diagnosed patients markedly decreased after treatment (P < 0.001). Additionally, the serum IL-21 levels in GD-goiter patients were higher than those of the GD-non-goiter patients (P < 0.001). However, no significant differences were found in the serum IL-21 levels in patients with or without Graves' ophthalmopathy. Importantly, serum IL-21 positively correlated with FT3, FT4, TPOAb, TGAb, and TRAb (r = 0.5053, r = 0.3266, r = 0.1792, r = 0.2445, and r = 0.4096, respectively; all P < 0.0001), and particularly with TSAb activity (r = 0.8171, P < 0.0001), negatively correlated with TSH (r = -0.2713, P < 0.0001). Serum IL-21 levels were significantly elevated in patients with GD and decreased after treatment; moreover, IL-21 may be associated with the clinical disease activity. These observations suggest that IL-21 may play an important role in the pathogenesis of GD.

The presence of adenosine A2a receptor in thyrocytes and its involvement in Graves' IgG-induced VEGF expression

Goitrogenesis in Graves' disease (GD) has been attributed to anti-TSH receptor antibody stimulation. Recently, a role for adenosine A2a receptor (A2aR) in goiter formation was reported in the thyroglobulin-A2aR transgenic mice. However, it is unclear whether A2aR is expressed in the thyroid and whether it is associated with the pathogenesis of goiter in GD. Here, we confirmed the expression of A2aR in FRTL-5 cells, primary normal human thyrocytes (both sexes were used without regard to sex), and thyroid tissue (both sexes were used without regard to sex) by PCR, Western blotting, immunohistochemistry, and immunofluorescence. After treatments with A2aR-specific agonist 2-p-(2-Carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine or GD IgG, the mRNA and protein levels of vascular endothelial growth factor (VEGF), a growth factor related to goitrogenesis, were evaluated along with upstream signaling pathways. A2aR activation and GD IgG promoted the expression of VEGF in thyrocytes, which was accompanied by the activation of cAMP/protein kinase A/phosphorylated-cAMP-response element-binding protein, peroxisome proliferator-activated receptor γ coactivator-1α, and hypoxia-inducible factor-1α. The changes induced by GD IgG were partially abrogated by A2aR small interfering RNA and an A2aR antagonist. These results were supported by data on the goiter samples from the thyrotropin receptor adenovirus-induced GD mouse model (female). These data demonstrate that GD IgG could up-regulate the VEGF expression through A2aR, indicating a potential mechanism for goitrogenesis in GD.

The effects of nonionic polymers on thyroid stimulation and TSH receptor binding by the human monoclonal TSH receptor autoantibody M22

BACKGROUND

Nonionic polymers such as polyethylene glycol (PEG), polyvinyl alcohol (PVA), and dextran amplify the ability of thyroid stimulating antibodies (TSAbs) from patients with Graves' disease to stimulate cAMP production in thyroid cells. Therefore we sought to determine if nonionic polymers also augment the effects of the human thyroid stimulating monoclonal antibody (M22) on isolated thyroid cells.

METHODS

The ability of nonionic polymers to alter the effects of M22 on certain parameters in porcine thyroid cells was examined. These parameters were augmentation of cAMP production (TSAb activity), inhibition of bovine thyrotropin (bTSH)-induced cAMP production (TBAb activity), and inhibition of bTSH binding to the TSH receptor (TSHR) (TBI activity).

RESULTS

Stimulation of cAMP production by M22 in porcine thyroid cells was augmented by PEG, PVA, and dextran in a manner similar to that of Graves' serum. In contrast, TSH-stimulated cAMP production was not increased by nonionic polymers. M22-stimulated cAMP production was completely inhibited by the sera of patients with TBAb activity, and this inhibition was diminished by PEG. M22 and TBI activity in first and second generation assays and this activity was not affected by PEG. Binding of biotin-M22 to TSHR-coated plate wells (third generation assay) was not significantly increased by co-incubation with polymers. PEG augmented the binding of (125)I-M22 to TSHR-coated tubes by twofold, but this was associated with a threefold increase in nonspecific binding. There was no increase in total and nonspecific (125)I-TSH binding. This means that PEG has less than a twofold augmentative effect on (125)I-M22 binding to the TSHR.

CONCLUSION

Nonionic polymers have similar effects in augmenting cAMP production in porcine thyroid cells in response to stimulation either by M22 or Graves' disease serum. The mechanism of this effect on the thyroid stimulating activity of M22 is unclear. The hypothesis that nonionic polymers augment M22 thyroid stimulation by increasing the mass of M22-occupied TSH receptors is not supported by the present study.

Modulation of Graves' disease autoantibody stimulation of recombinant human thyrotrophin receptor

BACKGROUND

The cAMP response of porcine thyrocytes to the immunoglobulin (Ig) fraction from Graves' sera is increased if these fractions are prepared with higher than usual concentrations of polyethylene glycol (PEG; 22.5% rather than 13.5%), leading to the suggestion that additional factors might exist in serum which influence the ability of autoantibodies to stimulate thyroid cells.

METHODS

We characterised the stimulatory activity of fractions prepared by differential PEG precipitation of Graves' sera, using heterologous eukaryotic cells expressing recombinant human thyrotrophin (TSH) receptor.

RESULTS

We found no evidence that material soluble in 13.5% PEG but precipitated by 22.5% PEG was stimulatory either on its own or in combination with the immunoglobulin-containing material precipitated by 13.5% PEG. Indeed, the stimulatory effect was reproduced by simply including low concentrations of PEG (1-4%) in the diluted sera from the majority of Graves' patients (12/18 tested) added to the target cells. Intriguingly, PEG had no effect on basal levels, with normal sera or stimulation by thyrotrophin.

CONCLUSIONS

The increase in stimulation reported when using immunoglobulins prepared with higher concentrations of PEG is attributable to a direct effect of the extra PEG (which had not been removed from the preparations) during the stimulation of the cells. Because the effect is observed with recombinant heterologous cells, it must be caused by interaction between PEG and the autoantibodies and/or the receptor-it cannot involve any other thyroid-specific molecule, although an involvement of other molecules widely distributed on many cell types is possible.