Background: The role of costimulatory molecules expressed on lymphocytes and thyrocytes in hyperthyroidism has attracted increasing attention and research has shown a close correlation between variant expression of these molecules on lymphocytes and thyrocytes and the development of GD.
Materials and methods: [corrected] Thyroid tissues were collected from GD patients during surgery and from Hashimoto disease (HT) and non-toxic goiter (NTG) patients as controls. ICOSL expression on infiltrated B cells and TFC was detected by flow cytometry (FCM), reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry (IHC). Variation in ICOSL expression on TFC in primary cultures was analyzed in the absence or presence of cytokines using FCM assays. The role of ICOS-ICOSL signaling in proliferation, thyroid hormone production and thyroglobulin (Tg) release was investigated in primary TFC cultures using ICOS gene transfected L929 cells (ICOS-L929 cells) and the blocking ICOSL antibody (11 C4) in MTT assays and radioimmunoassays.
Results and discussion: ICOSL expression on infiltrated B cells and TFC was detected in GD patient tissue. However, ICOSL expression was only detected on infiltrated B cells in control HT and NTG patient tissue. ICOSL expression on TFC was induced in vitro by the proinflammatory cytokines IFN-γ, IL-6 and TNF-α. Compared with mock transfected L929 (mock-L929) control cells, ICOS-L929 cells promoted significant proliferation of primary cultured TFC, with increased thyroid hormone and Tg production (all P < 0.01). TFC proliferation and production of thyroid hormones and Tg were inhibited significantly in the presence of ICOSL blocking antibody (11 C4) (all P < 0.05). Our observations suggest that ICOS-ICOSL signal plays a direct role in proliferation and differentiation of TFC and may exert important effects in the initiation, maintenance and exaggeration of autoimmune responses in local tissue.