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ABSTRACT

We studied the lymphocyte-induced alterations in hormonal metabolism and the production of tumour necrosis factor α (TNF-α) during coculture of thyrocytes and autologous lymphocytes from 20 patients with Graves' disease and from five normal subjects. Thyroglobulin (Tg) mRNA was assessed by slot-blot analysis under TSH stimulation. Tg, tri-iodothyronine (T₃) and cAMP secretion in the presence of TSH were measured by RIA after 3 or 5 days of coculture. TNF-α levels produced after 5 days incubation were also assayed in lymphocyte culture and coculture media.

Lymphocytes isolated from peripheral blood (PBLs) altered the production of Tg, T₃ and cAMP in autologous thyrocytes. Intrathyroidal lymphocytes (ITLs) decreased Tg and cAMP secretion but had no effect on T₃ secretion. The reductions in Tg and cAMP levels obtained with mechanically isolated ITLs (M-ITLs) were generally higher than those obtained with ITLs isolated by dispase (D-ITLs). No difference was seen between Graves' disease and normal cocultures. PBLs secreted large concentrations of TNF-α, larger than those obtained with M-ITLs whereas D-ITLs produced low amounts of this cytokine. In coculture, TNF-α levels were lower than those observed in lymphocyte culture. Significant correlations were obtained between TNF-α levels and the decrease in Tg, T₃ and cAMP concentrations. The percentage of T lymphocytes was higher in PBLs and D-ITLs than in M-ITLs. B lymphocytes levels were higher in ITLs, especially M-ITLs, than in PBLs. TNF-α production by B lymphocytes was maximal in M-ITLs.

In conclusion, lymphocytes induced a decrease in hormonal thyroid metabolism when cocultured with autologous thyrocytes. These perturbations may be attributed, at least partly, to TNF-α secreted by lymphocytes. TNF-α interacts via the adenylate cyclase pathway of TSH signal transduction.

ABSTRACT

We have studied the action of peripheral blood lymphocytes (PBLs) and intrathyroidal lymphocytes (ITLs) on the biochemical and hormonal metabolism of autologous thyrocytes cultured in follicles in a collagen gel. The production of tumour necrosis factor α (TNF-α) in culture was also measured. Thyroid tissues and lymphocytes were obtained from ten patients with Graves' disease and from five control subjects. Lymphocyte-induced cytotoxicity was evaluated in autologous thyrocytes cultured in a collagen gel by several tests: neutral red uptake, lactate dehydrogenase activity and glutathione level. Hormonal metabolism was assessed by evaluating tri-iodothyronine (T₃) and total cAMP production under TSH stimulation. TNF-α levels were measured in supernatants after 5 days of coculture. PBLs altered biochemical metabolism, T₃ synthesis and cAMP production in autologous thyroid follicles. These inhibitions were greater than those obtained with ITLs. No difference was seen between cells obtained from patients with Graves' disease and those from normal subjects. TNF-α levels secreted by PBLs were higher than those secreted by ITLs. The concentrations of this cytokine decreased in coculture. Significant correlations were observed between the decrease in biochemical and hormonal parameters and TNF-α levels. Exogenous TNF-α and high doses of interferon γ inhibited follicle metabolism, especially hormone secretion.

In conclusion, thyrocytes cultured in follicles provide a more sensitive model than monolayer cultures for analysis of lymphocyte-induced interactions. Lymphocytes gradually inhibit the biochemical and hormonal metabolism of autologous thyroid follicles depending on the isolation method. These alterations may be particularly attributed to TNF-α secreted by lymphocytes. The cytokine-induced inhibition of thyroid hormonal function apparently involves the adenylate cyclase system.