Effect of lymphocytes on hormonal secretion by autologous thyrocytes cultured in monolayers

We studied the lymphocyte-induced alterations in hormonal metabolism and the production of tumour necrosis factor alpha (TNF-alpha) 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-alpha 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-alpha, larger than those obtained with M-ITLs whereas D-ITLs produced low amounts of this cytokine. In coculture, TNF-alpha levels were lower than those observed in lymphocyte culture. Significant correlations were obtained between TNF-alpha 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-alpha 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-alpha secreted by lymphocytes. TNF-alpha interacts via the adenylate cyclase pathway of TSH signal transduction.