The effects of hyperthyroidism on experimental autoimmune thyroiditis in the rat.

The effects of hyperthyroidism on experimental autoimmune thyroiditis were investigated in the rat. Rats were given T4 twice daily by sc injection in amounts sufficient to raise circulating hormone levels 10-fold 4 h after administration. Thyroiditis was induced by immunization with rat thyroglobulin (Tg) in complete Freund's adjuvant, and the severity of the disease was assessed by comparison with saline-treated controls. Thymic and splenic hypertrophy were found in T4-treated animals, whereas lymph node wt decreased. The levels of Tg antibodies did not differ between animals given saline and those given T4, but the expected sustained rise in control animals was not seen in those treated with T4; in addition, there was a significant decrease in the amount of Tg antibody produced by in vitro culture of lymph node lymphocytes from T4-treated rats. Continuous T4 administration lowered the number of T cells in the circulation, but the number of phenotypically identified helper cells remained the same. The most striking effects of T4 were to ameliorate the intensity of histologically defined thyroiditis and lower the response of lymph node T cells to the nonspecific mitogen, phytohemagglutinin. These results show that excessive T4 does not, as previously suggested, enhance the immune response in autoimmune thyroid disease: on the contrary, suppression is found with the dose and model we have used. In view of the magnitude of this effect, it is now important to identify the site of T4 action and investigate how this effect contributes to the autoimmune response in Graves' disease.

Enzyme-linked immunoassay of monoclonal and serum microsomal autoantibodies.

An automated enzyme-linked immunoassay for the detection of antibodies to human thyroid microsomes has been assessed. This assay correlated closely with the established commercial passive haemagglutination method. Variations in the purity of crude microsome preparations and the degree of thyroglobulin contamination make careful comparison of different preparations essential for meaningful interpretation of results, and attempts to circumvent these problems by further purification of microsome preparations using gel filtration are discussed. The application of this method for routine screening of serum samples is demonstrated using populations of normal subjects and patients with rheumatoid arthritis and anti-glomerular basement membrane disease. This assay has also permitted the establishment of murine hybrid myelomas secreting monoclonal antibodies to human thyroid microsomes.

The influence of cyclosporin a on experimental autoimmune thyroid disease in the rat.

Female PVG/c rats, thymectomized on weaning and given 4 courses of whole body irradiation to a total dose of 1000 rads, developed experimental autoimmune thyroid disease (EAITD) as assessed by histological evidence of thyroiditis and circulating levels of antithyroglobulin antibodies. Hypothyroidism resulted. Induction of the disease was associated with a highly significant fall in T lymphocyte numbers. Eight weeks after their last dose of irradiation the animals commenced treatment with Cyclosporin A (10 mg/kg rat/day, intragastrically) and were treated for varying time intervals thereafter. The reversal of the T lymphocyte helper: suppressor ratio on Cyclosporin A therapy was associated with a significant improvement in the disease process. The alterations in the T cell subsets and in the disease lasted only as long as the drug was administered and thereafter reverted towards that seen in the control groups of animals receiving no treatment.

Analysis of the spectrotypes of autoantibodies against thyroglobulin in two rat models of autoimmune thyroiditis.

We have studied the isoelectric focusing (IEF) spectrotypes of autoantibodies against thyroglobulin in two rat models of Hashimoto's thyroiditis: (1) AUG strain rats immunized with autologous thyroglobulin in Freund's complete adjuvant; (2) PVG/c strain rats which have been thymectomized and sublethally irradiated. The IEF spectrotypes revealed differences between the two models. The anti-thyroglobulin response in immunized AUG rats is mainly oligoclonal or polyclonal, often with dominant clones in the spectrotype, similar to about 90% of Hashimoto's patients, whereas the response in the PVG/c rat is highly restricted. There were pronounced changes in spectrotype with time in the PVG/c, but not AUG, rats with considerable variation in the lifespan of individual clones. The maximum lifespan of an anti-self secreting B-cell clone in the PVG/c rat, determined by persistence of its clonotype, was at least 16 weeks.

Immunological events leading to destructive thyroiditis in the AUG rat.

Single or infrequent observations in patients or animals with autoimmune thyroid disease (AITD) have failed to elucidate the exact sequence of pathogenetic events leading to thyroid cell destruction. A detailed serial morphological and functional study of experimental AITD (EAITD) in the female AUG rat was therefore undertaken. Following induction of EAITD with thyroglobulin (Tg) in adjuvant antibodies to Tg were detectable one week after the initial immunization, at which stage Ia positive vascular endothelium was observed within the thyroid. This was followed by large numbers of Ia positive dendritic-like cells. With time, in almost all the animals whose titre of Tg antibody rose above a critical level, lymphocytic infiltration was observed consisting mainly of Ia positive B cell aggregates with fewer scattered T cells. This was associated with raised levels of serum TSH and concomitant focal follicular hyperplasia and necrosis. Expression of Ia was mainly restricted to the outer epithelial wall of follicular thyrocytes in direct contact with invading lymphoid cells, although occasional staining on the internal apical membrane was observed as a late event in the destructive process. The Ia expression on thyroid epithelial cells was only observed in areas of thyroid lymphoid infiltration. The immune infiltration of the thyroid in the AUG rat appears to be very similar to that observed in Hashimoto's thyroiditis, with the exception that Ia was not regularly observed on the apical surfaces of thyrocytes. Whether or not the diminished or absent epithelial Ia expression contributes to the spontaneous recovery of the disease observed in this model remains to be resolved.

The tissue distribution of thyroglobulin-responsive B and T cells in experimental autoimmune thyroiditis (EAT).

The tissue distribution of thyroglobulin antibody producing lymphocytes has been studied during the course of immunisation-induced experimental autoimmune thyroiditis in the rat. The iliac lymph nodes were initially the most important source of autoantibody but later in the disease the bone marrow and thyroid-draining lymph nodes were also involved. In addition small amounts of thyroglobulin antibody were made by thyroid-derived lymphocytes. A blastogenic response to thyroglobulin was found using lymphocytes from the iliac nodes initially and later from the spleen. These results demonstrate the widespread and sequential involvement of the lymphoid system in the autoimmune response to thyroglobulin.

The role of the spleen in experimental autoimmune thyroiditis.

We have investigated the role of the spleen in the humoral and cellular immune response of rats with experimental autoimmune thyroiditis (EAT) induced by immunization with thyroglobulin and Freund's complete adjuvant. Animals subjected to splenectomy within 4 days of immunization developed lower thyroglobulin antibody levels and less severe thyroiditis compared to sham operated controls. There was no impairment in the ability of the animals to recover spontaneously from the disease after splenectomy. Together with the results obtained using splenocyte infusions, this suggests that suppressor cell production within the spleen plays only a small part in the normal immunological control which is presumably responsible for spontaneous regression of the disease.

The influence of lithium chloride on experimental autoimmune thyroid disease.

Lithium administration is known to be associated with the development of thyroid dysfunction; it also exerts an effect on the immune system. The effect of lithium on experimental autoimmune thyroid disease was studied in female August rats. Following immunization with rat thyroglobulin in Freund's complete adjuvant, lithium chloride was administered i.p. for 30 days to four groups at varying stages of the disease. Control animals received i.p. saline. Anti-thyroglobulin antibody levels (measured by ELISA) were significantly increased in rats given lithium immediately post-immunization (group B) compared to control animals (661 +/- 42 OD vs 448 +/- 68; mean +/- s.e., P less than 0.02). In contrast, animals which received lithium during the spontaneous resolution of the disease (group D) showed a significant fall in anti-TG antibody compared to controls (99 +/- 15 vs 27 +/- 15; P less than 0.001). Anti-TG antibody levels remained undetectable in animals which received lithium but were not immunized. The splenic T cell blastogenic response (as measured following phytohaemagglutinin stimulation) was significantly increased in rats receiving lithium prior to and during immunization (group A) (stimulation index 63.4 +/- 6.9 vs 10.2 +/- 2.4; P less than 0.001). Spontaneous cell proliferation of splenic lymphocytes was decreased in two lithium treated groups (group A P less than 0.005, group C P less than 0.05). There was no alteration in splenic weight or the degree of thyroid lymphocytic infiltration in any of the treated group. Lithium exerted both positive and negative influences on the immune system in rats immunized with thyroglobulin in adjuvant but did not induce autoantibody production in normal rats.

The influence of cyclosporin A on the induction of experimental autoimmune thyroid disease in the PVG/c rat.

Using an experimental model of autoimmune thyroid disease we have investigated the influence of cyclosporin A (CyA) on the induction of the disease and its potential ability to prevent disease development. PVG/c rats (n = 80) neonatally thymectomized (day 21) and thence sublethally irradiated were divided into eight groups and received either no CyA or oral CyA (10 mg/kg body weight) for varying periods prior to and during disease induction. Serial serum measurements of thyrotropin (TSH) by radioimmunoassay and anti-thyroglobulin autoantibody by enzyme linked immunosorbent assay showed a progressive rise in untreated animals. The rise in serum TSH levels from 349 +/- 15 ng/ml (mean +/- s.e., normal less than 400 ng/ml) at 7 weeks of age to 526 +/- 61 ng/ml at 11 weeks and 820 +/- 54 ng/ml at 15 weeks was not significantly different in animals treated with CyA for periods ranging from 24 h prior to thymectomy to 7 days post-thymectomy. In contrast animals treated for 28 days post-thymectomy showed significantly lower levels of TSH at both 11 weeks (391 +/- 26; P less than 0.02) and 15 weeks (587 +/- 37; P less than 0.005) as compared with untreated animals. Similar though less dramatic changes were seen in intermediate groups. Autoantibody levels in untreated animals rose from initially undetectable levels to 0.451 +/- 0.07 OD (mean +/- s.e.) at 11 weeks and 0.581 +/- 0.041 OD at 15 weeks. Animals treated for at least 4 weeks after thymectomy with CyA had significantly lower levels of antibody at both 11 weeks (0.213 +/- 0.01; P less than 0.001) and 15 weeks (0.337 +/- 0.03; P less than 0.001) of age. Intermediate groups ranged in antibody levels depending on the duration of CyA treatment. Thyroid gland weight (12.7 +/- 2.4 mg/100 g body weight, mean +/- s.e.) and histological grade of thyroiditis (1.8 +/- 0.4, mean +/- s.e.) in the animals treated with CyA for 4 weeks, assessed when the animals were killed at 15 weeks, were smaller and had less severe thyroiditis than untreated thymectomized and irradiated animals (23.8 +/- 2.8 mg/100 g, P less than 0.02 and 2.9 +/- 0.2, P less than 0.05) killed at the same time. CyA given for long enough during induction of experimentally-induced autoimmune thyroid disease delayed the onset of disease and reduced its severity but could not prevent it given over time courses ranging from 48 h prior to thymectomy to 4 weeks after.(ABSTRACT TRUNCATED AT 400 WORDS)