In order to investigate the regulation of autoimmune response to thyroglobulin (Tg), one of the thyroid autoantigens, we established a Tg-specific T cell line by stimulation of peripheral blood mononuclear cells from a healthy volunteer with Tg and characterized its cytokine production pattern. The Tg-specific Tcell line, designated DH5D1, obtained from a limiting dilution culture bore ap”Tcell receptor and was CD4 and CD45RO positive. Upon stimulation with Tg, DH5D1 secreted little or no titers of IL-2, TNF-a, and IFN-γ, whereas activation with combination of phorbor myristate acetate and calcium ionophore produced measurable levels of these cytokines. These results indicate that the Tg-specific T cell line is not defective in its capacity to produce proinflammatory cytokines and suggest that the inability of cytokine production by autoreactive T cells of healthy individuals is one fail-safe mechanism for preventing aggression of harmful autoimmune response.