Use of plaque assays to study thyroglobulin autoantibody synthesis by human peripheral blood lymphocytes

Plaque assays have been used to study thyroglobulin autoantibody synthesis and total immunoglobulin production by cultures of peripheral blood lymphocytes from patients with Hashimoto's thyroiditis. Freshly isolated Hashimoto or normal lymphocytes contained small numbers (7-1300) of total IgG plaque-forming cells (PFC) and total IgM PFC, but specific thyroglobulin antibody PFC was undetectable. After 5-8 days' culture with pokeweek mitogen (PWM), total IgG and IgM PFC were markedly increased to a geometric mean of 10,140 (8414-12,220) IgG PFC and 3450 (163-7534) IgM PFC per 10(6) cultured lymphocytes (95% confidence limits in parentheses). Furthermore, a mean of 63 (22-287) specific IgG thyroglobulin antibody PFC per 10(6) lymphocytes were detectable in cultures of Hashimoto lymphocytes. The IgG thyroglobulin antibody PFC were stimulated by Epstein-Barr virus (EBV) infection, suggesting that EBV infection may be useful in obtaining monoclonal thyroid autoantibodies.

Acetylcholine receptor antibody synthesis in lymphocyte cultures

The synthesis of immunoglobulin and acetylcholine receptor antibody by lymphocytes extracted from the peripheral blood and thymus of patients with myasthenia gravis was investigated using the Marbrook culture system. Small amounts of immunoglobulin were synthesised by thymic lymphocytes cultured in medium without mitogen for 14 days and acetylcholine receptor antibody activity was detectable in cultures from 3 out of 5 patients with thymic hyperplasia. Addition of Pokeweed mitogen to the cultures increased both IgG and acetylcholine receptor antibody synthesis and under these conditions receptor antibody activity was detectable in all 5 thymic lymphocyte cultures studied. Peripheral blood lymphocytes also produced small amounts of IgG when cultured in the absence of mitogen but acetylcholine receptor antibody levels were undetectable. In the presence of Pokeweed mitogen, however, peripheral blood lymphocytes synthesised increased amounts of IgG and acetylcholine receptor antibody activity was detectable in cultures of lymphocytes from 3 out of 4 patients. The amount of acetylcholine receptor antibody per microgram IgG, the specific activity, was greater in cultures of thymic lymphocytes than the specific activity of IgG in serum, suggesting that the hyperplastic thymus may be a major site of acetylcholine receptor antibody synthesis. Therefore it should be possible to use the culture system described to investigate the processes involved in the breakdown of self-tolerance in myasthenia gravis.

Cyclosporin A promotes spontaneous outgrowth in vitro of Epstein-Barr virus-induced B-cell lines

Cyclosporin A (CSA) is a fungal metabolite which exerts profound effects on the immune system and has potential as a selective immuno-suppressive agent. Clinical trials with human renal allograft recipients have confirmed this potential but there have been disturbing reports of lymphoma in a significant number of patients. Despite extensive animal studies, the specificity of this drug for human lymphocyte subpopulations is largely unknown. We demonstrate here that in vitro CSA has no apparent effect on Epstein-Barr virus (EBV)-induced B-lymphocyte activation, but totally inhibits the T-cell dependent pokeweed mitogen (PWM) B-cell response. In addition, CSA markedly facilitates the outgrowth of B-lymphoblastoid cell lines from both EBV-infected and non-infected lymphocytes of EBV immune donors cultured in vitro. These results indicate that CSA can interfere with the lymphocytes normally responsible for maintaining the life-long carrier state initiated by primary infection with EBV, allowing outgrowth of the persistently infected cells circulating in the peripheral blood.

Carbimazole and the autoimmune response in Graves' disease

Microsomal antibodies and antibodies directed toward the receptor for thyroid-stimulating hormone (TSH) decreased in parallel while patients with Graves' disease were taking carbimazole, whereas no significant changes were observed during treatment with placebo or propranolol. The changes in autoantibody levels during carbimazole treatment were independent of changes in serum thyroxine and could have been due to a direct effect of the drug on autoantibody synthesis. Evidence for this suggestion was provided when low doses of methimazole (the active metabolite of carbimazole) were found to inhibit thyroid-autoantibody production in cultured lymphocytes. Since thyroid lymphocytes are probably a major site of thyroid-antibody synthesis in Graves' disease and methimazole is concentrated in the thyroid during treatment, a local action of the drug on antibody production seems likely. This possibility could be important in the use of carbimazole to control hyperthyroidism.

In vitro studies on the control of thyroid autoantibody synthesis

A current hypothesis suggests that autoimmune responses are prevented in normal individuals by a population of suppressor cells. We have investigated this using a system in which thyroid autoantibodies are synthesised in culture by peripheral blood mononuclear cells (PBM) from patients with Hashimoto's thyroiditis. A group of 8 Hashimoto patients and 17 normal subjects were used in the study. PBM from the group of patients did not differ significantly from those of the control group in terms of their ability to synthesise IgG in culture, to respond to allogeneic cells or to PHA. (Nor were any genetic differences observed between the two groups in terms of HLA-A, B or C antigens.) In 6 co-culture experiments involving equal numbers of PBM from patients and normal donors, inhibition of thyroid antibody production was not observed. Additionally, T-cell enriched populations from 2 normal donors were unable to specifically inhibit thyroid antibody synthesis by Hashimoto B-cell enriched fractions from 2 Hashimoto patients. Consequently, we were unable to show suppressor cell activity in normal PBM and it is suggested that these cells may need to be activated by antigen before their presence can be demonstrated.

Effect of irradiation on thyroid-autoantibody production

Irradiated lymphocytes have been found to stimulate thyroid-autoantibody synthesis by lymphocyte cultures. It is proposed that a similar effect is involved in the increased autoimmune response which follows radioiodine treatment for Graves' disease.

Kinetics of immunoglobulin production by cultured human peripheral blood lymphocytes

A study of immunoglobulin synthesis by human peripheral blood lymphocytes cultured in Marbrook flasks is described. Maximal amounts of immunoglobulin were produced by 3 weeks and most of this was synthesised between 6 and 21 days. In the region of 90% of the immunoglobulin was secreted into the medium. Pokeweed mitogen (PWM) stimulated cultures produced about 10 times as much immunoglobulin as cells cultured in medium only. After 21 days stimulated cultures produced about 150 microgram of IgG, 125 microgram of IgM and 50 microgram of IgA per 10(7) cells.

Thyrotropin receptors in adipose tissue, retro-orbital tissue and lymphocytes

Thyrotropin (TSH) receptors on retro-orbital muscle and fat have been implicated in the pathogenesis of Graves' exophthalmos and it has been suggested that TSH has a direct effect on human fat metabolism. We have therefore investigated the interaction of biologically active 125I-labelled TSH with membranes prepared from human adipose, retro-orbital and thyroid tissue. Since lymphocytes contain receptors for several polypeptide hormones, TSH binding to lymphocyte membranes was also studied. We were unable to demonstrate TSH receptors in adult human adipose tissue, retro-orbital muscle and fat, or peripheral blood lymphocytes. In contrast, adult and neonatal guinea pig adipose tissue membranes showed similar TSH binding characteristics to guinea pig thyroid membranes.

The influence of propranolol on the thyrotropin receptor

Propranolol, a beta adrenergic blocking drug, is known to inhibit the thyrotropin (TSH) stimulation of adenosine-3',5'-monophosphate (cyclic AMP production in thyroid membranes but the mechansim of this inhibitory action is known. We have therefore investigated the influence of propranolol on the binding of 125I-labelled TSH to human thyroid membranes. Both d- and l-propranolol were found to enhance the binding of 125I-labelled TSH to thyroid membranes. The amount of label bound increased from about 30% in the absence of propranolol to about 60% in the presence of 3.3 x 10(-3)M propranolol. Scatchard analysis of the binding data indicated that propranolol increased the association constant of the thyrotropin-thyrotropin receptor interaction. Practolol, lithium carbonate, methimazole, and somatostatin had no effect on thyrotropin binding. This effect of propranolol appeared to be due to a direct reversible action of propranolol on the thyroid membranes and could be attributed to the membrane-disrupting properties of the drug rather than its beta-blocking activity. The increased TSH receptor occupancy which resulted from the increased association constant of the TSH-thyroid membrane interaction corresponded with a decrease in TSH-stimulated cyclic AMP formation. These data could indicate that propranolol reduced the efficiency of the receptor-adenylyl cyclase coupling system.