Subacute thyroiditis: activated HLA-DR and interferon-gamma expressing T cytotoxic/suppressor cells in thyroid tissue and peripheral blood

Thyroid cell survival in coculture with autologous peripheral or intrathyroidal lymphocytes

OBJECTIVE

We have studied lymphocyte induced cytotoxicity and the production of interferon gamma (IFN-gamma) and tumour necrosis factor alpha (TNF-alpha) during coculture of thyrocytes and autologous lymphocytes from patients with Graves' disease and from normal subjects.

PATIENTS

Thyroid tissues and lymphocytes were obtained from 28 patients with Graves' disease and from 9 control subjects.

MEASUREMENTS

Lymphocyte induced cytotoxicity was evaluated on autologous thyrocytes using 5 metabolic tests: the MTT assay, the neutral red uptake, lactate dehydrogenase measurement and glutathione assay. IFN-gamma and TNF-alpha measurements were performed after 1, 5 or 7 days' coculture.

RESULTS

The lymphocytes isolated from peripheral blood (PB lymphocytes) altered the morphology and the metabolism of autologous thyrocytes. The intrathyroidal lymphocytes isolated after Dispase digestion were not toxic whereas mechanically isolated lymphocytes exerted a little toxicity. No difference was seen between Graves' disease and normal cells. The supernatants from cocultures had higher IFN-gamma levels than those from lymphocyte cultures. In coculture, PB lymphocytes secreted more IFN-gamma and TNF-alpha than intrathyroidal lymphocytes. The PB lymphocyte induced cytotoxicity was not due to IFN-gamma and TNF-alpha alone.

CONCLUSION

Peripheral blood lymphocytes are cytotoxic in vitro to autologous thyrocytes whereas intrathyroidal lymphocytes exert little or no cytotoxicity according to their isolation method. The mechanisms of lymphocyte induced toxicity remain to be explained.

Granulomatous and lymphocytic thyroiditis associated with a follicular adenoma

A 44-year-old woman came to medical attention with right thyroid lobe enlargement and weight loss. Thyroid scan and ultrasound demonstrated a nodule in the right thyroid lobe; a right hemithyroidectomy was performed. Histologic examination documented granulomatous and lymphocytic thyroiditis associated with a follicular adenoma. No inflammation was apparent within the adenoma. The parallels between granulomatous thyroiditis and lymphocytic thyroiditis, including presumed viral initiation and deranged immunologic function, suggest that granulomatous thyroiditis may evolve into chronic lymphocytic thyroiditis; this case may be an example of such a transition. It is proposed that thyroid follicular adenomas have different antigenicity, which may account for the conspicuous absence of inflammation within the tumor.

Evaluation of a radioreceptor assay for TSH receptor autoantibodies

A commercial radioreceptor assay for TSH receptor autoantibodies (TRAb), based on solubilized porcine receptor and purified radio-iodinated bovine TSH, was tested in 264 subjects with a variety of thyroid disorders. The sensitivity of the assay for the detection of hyperthyroid Graves' disease was 91%. The assay specificity for Graves' disease was 95%. With the exception of one patient with Hashimoto's disease and one patient with de Quervain's subacute thyroiditis no subjects other than Graves' patients had detectable TRAb. Thus purely blocking TSH receptor autoantibodies were not detected with the assay. One female with thyroxine-treated idiopathic primary hypothyroidism who had given birth to two children with transiently elevated TSH, was found to have a circulating TSH-binding substance that resulted in an abnormally negative TRAb value, and highly discrepant results when TSH was measured with a double antibody TSH radioimmunoassay and an immunoradiometric assay. The TSH-binding substance was precipitated like a protein, but was not IgG. Similar findings have not previously been reported.

Pathogenetic aspects of organ-specific autoimmunity

In the last few years a great deal of information on the etiopathogenetic aspects of organ-specific autoimmune diseases (OSADS) has been obtained. It has been shown that genetic factors play an etiologic fundamental role. They are responsible for the dysregulation of the immune system and for the target organ susceptibility which favour the onset of the diseases. Putative environmental factors, such as viral infections, can act as initiating or precipitating events only in genetically predisposed individuals. Immunological mechanisms capable of triggering autoimmune responses have been demonstrated. Data obtained from experimental models and from humans suggest that the ongoing expansion of autoreactive T cells with specificity for autoantigens (AAgs) can be considered as the main immunological event capable of inducing and maintaining the target organ damage. These cells can activate different effector systems, i.e., autoantibody (AAb)-producing B cells, cells with cytotoxic activity, etc., by releasing different combinations of lymphokines. In overt diseases AAbs are directly involved in the pathogenesis of lesions due to autoimmune responses against functional molecules and cellular receptors. The pathogenesis of the common inflammatory destructive lesions of the target organs is more complex and not yet clarified. A large proportion of T cells present in the inflammatory infiltrates are apparently not directed to the AAgs. Most cells display cytolytic activity and may contribute to tissue damage by releasing lymphokines which activate other cells and cascade the process. Vicious cycles, i.e., upregulation of class II and I molecules, alterations of the cytokine network, etc., are supposed to be involved in the maintenance of target organ lesions.

Induction of circulating activated suppressor-like T cells by methimazole therapy for Graves' disease

Thyrostatic drug treatment of Graves' disease suppresses excessive thyroid hormone synthesis and causes a parallel decrease in serum thyroid autoantibody levels. The mechanism of this immunosuppression is unknown. We studied methimazole-induced immunoregulatory effects prospectively in 14 patients with Graves' disease treated for up to six months. The numbers of circulating activated, HLA-DR-positive T helper/inducer cells decreased gradually, from 8.3+1.7 percent (+SD) to 1.0+1.7 percent (P less than 0.001). HLA-DR-positive T suppressor/cytotoxic cells increased transiently at one month, from 2.0+1.9 percent to 12.6+6.4 percent (P less than 0.001), and returned to 2.9+3.7 percent at six months. Methimazole did not alter the HLA-DR expression of T cells in vitro. In two patients, the helper activity of T cells in inducing autoantibody secretion in vitro was substantially reduced after one month of methimazole treatment. Before treatment, large proportions of thyroid-infiltrating T-cell subsets expressed the activation markers HLA-DR, interferon-gamma, and interleukin-2 receptors, which were partially lost during therapy. Methimazole treatment was accompanied by a gradual reduction in circulating levels of thyrotropin-receptor, microsomal, and thyroglobulin autoantibodies. These results are compatible with the view that methimazole-induced immunoregulation in Graves' disease is mediated by a direct inhibitory effect on thyrocytes. This inhibition is in turn accompanied by marked changes in the proportions of activated T helper-like and T suppressor-like cells. This altered T-cell activation profile reflects, at least in part, the functional suppression of autoantibody production observed in methimazole-treated patients with Graves' disease.