Makoto Iitaka

Lack of Effect of Methimazole on Thyrocyte Cell-Surface Antigen Expression

The nature of the immunosuppressive effect of antithyroid drugs has been a subject of controversy. It has been claimed that these agents exert a direct effect on the immune system, although we and others have suggested that the drugs affect the thyroid cells primarily with consequent reduced thyrocyte-immunocyte signalling. This may occur from reduced thyroid hormone production and/or reduced antigen presentation by the thyrocytes to local T lymphocytes. Using a cytotoxicity assay system, with chromium-51 labelling, monoclonal antibodies against thyroperoxidase (TPO) and HLA-DR, and complement, we have measured the expression of TPO and HLA-DR on cultured normal human thyroid cells; we have also measured thyroglobulin (Tg) release by radioimmunoassay into the medium of the cultured cells. The thyroid cells were stimulated with TSH or thyrotropin binding inhibitory immunoglobulin (TBII) for 48 hours before measuring for TPO induction, and with interferon gamma (IFN-gamma) (with or without TSH or TBII) for thyrocyte HLA-DR expression. A dosage of 1.6 milliunits per ml of TSH resulted in a significant increase in TPO expression on thyrocytes when compared with control unstimulated thyroid cells (p less than 0.001). The concentrations of Tg released into the medium with TSH or TBII were also significantly higher than those of the control thyrocytes. IFN-gamma at 200 units per ml induced HLA-DR expression, but did not induce thyrocyte TPO expression, or Tg release. Addition of the antithyroid drug, methimazole (MMI), at different concentrations, in addition to the other stimulators, IFN-gamma, TSH, or TBII, did not result in any inhibition of TPO, Tg release, or HLA-DR expression on the thyroid cells. It would thus appear that the pathways for stimulation for the expression of TPO and HLA-DR appear to be different. Finally, MMI does not cause its immunosuppressive effect by any reduction of thyroid antigen expression or release.

Sensitization of T lymphocytes to thyroid antigen in autoimmune thyroid disease as demonstrated by the monocyte procoagulant activity test

Monocyte procoagulant activity (PCA) production has been reported to have a close relation to cell-mediated immunity (CMI), and the collaboration of T lymphocytes is necessary to induce PCA. Antigen-specific sensitization of lymphocytes in patients with Graves’ disease (GD) and Hashimoto’s thyroiditis (HT) has been demonstrated by means of the production of cell-bound PCA by monocytes following antigen stimulation of whole peripheral blood mononuclear cells (PBM). These cells, obtained from both normal subjects and patients with autoimmune thyroid diseases, produced significant amounts of PCA with non-specific lectin, concanavalin A (Con A) stimulation; however, there was no significant difference between the two groups, suggesting that Con A stimulated T cells induced monocyte PCA nonspecifically. Peripheral mononuclear cells from patients with autoimmune thyroid diseases produced significantly greater amounts of PCA than PBM from normal subjects when stimulated with solubilized and IgG-free thyroid antigen. On the other hand, liver antigen did not induce significant amounts of PCA production in PBM from either normal subjects or patients. Significantly larger amounts of PCA were produced by PBM from patients following thyroid antigen stimulation than with liver antigen stimulation. Although monocytes were the major source of PCA, T cells were necessary to induce PCA in monocytes with thyroid antigen and Con A stimulation. Elimination of lymphocyte subsets in PBM from patients by negative selection (using monoclonal antibodies and complement) suggested that the collaboration of T lymphocytes, especially helper/inducer (T4+) T cells, was necessary to produce PCA with thyroid antigen stimulation. These data provide evidence that patients with autoimmune thyroid disease have sensitized T (helper/inducer) lymphocytes to thyroid antigen, which can induce monocyte PCA with thyroid antigen stimulation.

IMMUNOMODULATORY EFFECT OF THE TREATMENT OF GRAVES’DISEASE ON ANTIGEN‐SPECIFIC MONOCYTE PROCOAGULANT ACTIVITY PRODUCTION

The monocyte procoagulant activity (PCA) production assay has been shown to be a good parameter of cell‐mediated immunity. We have studied antigen‐specific PCA production in peripheral blood mononuclear cells from patients with Graves’disease to determine the effect of the treatment on the cell‐mediated immune response. Peripheral blood mononuclear cells from patients with untreated or relapsed Graves’disease produced significantly greater PCA with thyroid antigen stimulation than those from normal subjects. Patients both on antithyroid drugs in the hyperthyroid state and within 3 months post‐131I therapy also produced significantly larger amount of PCA than normal subjects. However, there was no significant difference in PCA production with thyroid antigen stimulation between normal subjects and patients on anti‐thyroid drugs in the euthyroid state, or patients over 3 months post‐131I therapy. The ratio of positive to negative PCA production in patients on anti‐thyroid drugs in the euthyroid state or over 3 months post‐131I therapy was significantly lower than in untreated or relapsed Graves’disease patients. Mononuclear cells from patients on propylthiouracil responded to propylthiouracil in vitro by production of PCA. Cells from normal subjects, untreated Graves’disease patients, or patients with Hashimotos thyroiditis did not produce PCA with propylthiouracil stimulation. Mononuclear cells from patients who were on propylthiouracil for more than 3 months produced greater PCA than those on the drug for less than 3 months, suggesting sensitization of lymphocytes to propylthiouracil during the course of treatment. However, after 131I therapy, they gradually became unresponsive to propylthiouracil. This study has shown that the activity of the antigen‐specific response assessed by PCA production in mononuclear cells from Graves’disease patients declined after treatment, suggesting that the treatment exerted immunomodulatory effects.