T-cell restriction in thyroid eye disease

Mechanisms That Underly T Cell Immunity in Graves' Orbitopathy

Graves' orbitopathy (GO), also known as thyroid-associated ophthalmopathy, is the most common ocular abnormality of Graves' disease. It is a disfiguring, invalidating, and potentially blinding orbital disease mediated by an interlocking and complicated immune network. Self-reactive T cells directly against thyroid-stimulating hormone receptor-bearing orbital fibroblasts contribute to autoimmune inflammation and tissue remodeling in GO orbital connective tissues. To date, T helper (Th) 1 (cytotoxic leaning) and Th2 (antibody leaning) cell subsets and an emerging role of Th17 (fibrotic leaning) cells have been implicated in GO pathogenesis. The potential feedback loops between orbital native residential CD34^- fibroblasts, CD34⁺ infiltrating fibrocytes, and effector T cells may affect the T cell subset bias and the skewed pattern of cytokine production in the orbit, thereby determining the outcomes of GO autoimmune reactions. Characterization of the T cell subsets that drive GO and the cytokines they express may significantly advance our understanding of orbital autoimmunity and the development of promising therapeutic strategies against pathological T cells.

Thyroid dermopathy and acropachy

Graves' disease is an autoimmune condition commonly associated with thyroid dysfunction and with anti-thyroid antibodies, usually TSH receptor stimulating antibodies. Thyroid autoimmunity also may be associated with extra thyroidal manifestations. Most common extra thyroidal manifestation is ophthalmopathy. Less common is thyroid dermopathy, usually occurring in pretibial area. Dermopathy is almost always associated with ophthalmopathy and in severe cases with acropachy. A common antigen with thyroid in tissues of the skin and the eyes, most likely TSH receptor, is involved in pathogenesis of extra thyroidal manifestations. Presence of dermopathy and acropachy are predictors of severity of autoimmune process. Local corticosteroid application is the standard therapy for dermopathy. Response to therapy is good in mild cases and poor in severe cases. Immune modulators and biotherapies are undergoing randomized trials for ophthalmopathy component of Graves' disease. Any therapy proven to be effective for ophthalmopathy can be utilized in future for management of dermopathy.

New insights into antibody-mediated hyperthyroidism

The most common cause of hyperthyroidism is Graves' disease, which represents a typical example of an organ-specific autoimmune condition. The exact triggers for the disease remain unknown, but are likely to involve a complex interaction between multiple environmental factors in a genetically predisposed individual. The main feature of the condition is the presence of thyroid-stimulating antibodies, which activate the thyroid- stimulating hormone receptor, resulting in hyperthyroidism. These antibodies may also be involved in the extrathyroidal complications of the disease. The recent generation of thyroid-stimulating antibodies in animal models and the isolation of monoclonal thyroid-stimulating antibodies from a patient with Graves' disease should allow the detailed study of thyroid-stimulating antibodies-thyroid-stimulating hormone receptor interactions. This will help to shed more light on disease pathogenesis and may offer new treatment strategies in difficult cases, particularly in patients with extrathyroidal complications.

T-cell-mediated immunity in thyroid-associated ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is considered to be an autoimmune inflammatory disorder of the extraocular muscles and the orbital fat/connective tissue. Recent studies analyzing T cells infiltrating retrobulbar tissues generated important insights into the immunopathogenesis of TAO. The present review focuses on advances in our understanding of mechanisms responsible for the autoimmune inflammation in TAO, especially T cell migration to the inflammatory site, T cell activation by autoantigens and costimulatory signals and their cytokine profile. The elucidation of these processes might lead to the development of novel therapeutic strategies directed against autoreactive T cells.

Thyroid-associated ophthalmopathy: clinical features, pathogenesis, and management

Thyroid-associated ophthalmopathy (TAO) is a progressive eye disorder characterized by immune-mediated inflammation of the extraocular muscles and orbital connective tissue. TAO is linked, in a unique way, with thyroid autoimmunity, in particular Graves' hyperthyroidism. Our working hypothesis for the pathogenesis of TAO is that recognition of a thyrotropin receptor (TSHR)-like protein in the orbital preadipocytes by antibodies may be the initial event leading to homing of lymphocytes into the orbital tissues. In the course of thyroid inflammation, antibodies and T cells reactive against G2s expressed in thyroid membranes cross-react with the protein in the eye muscle fiber, leading to eye muscle damage and dysfunction. Those patients with anti-G2s antibodies develop ocular myopathy. Antibodies against flavoprotein, the 64-kDa protein, which are produced in the context of eye muscle fiber damage and mitochondrial rupture, are sensitive markers of immune-mediated fiber necrosis in patients with ophthalmopathy but do not directly damage the eye muscle. Antibodies against type XIII collagen, which is localized in the plasma membranes of orbital fibroblast, may be a new marker for the congestive ophthalmopathy subtype of TAO. The measurement of antibodies against key eye muscle and orbital connective tissue autoantigens may have a role in the management of active ophthalmopathy and its prediction in patients with Graves' hyperthyroidism.

Management of Graves' ophthalmopathy: reality and perspectives

Graves' ophthalmopathy is an debilitating disease impairing the quality of life of affected individuals. Despite recent progress in the understanding of its pathogenesis, treatment is often not satisfactory. In mild cases, local therapeutic measures (artificial tears and ointments, sunglasses, nocturnal taping of the eyes, prisms) can control symptoms and signs. In severe forms of the disease (3-5%), aggressive measures are required. If the disease is active, high-dose glucocorticoids and/or orbital radiotherapy, or orbital decompression represent the mainstay of treatment. If the disease is severe but inactive, orbital decompression is preferred. Novel treatments such as somatostatin analogs or intravenous immunoglobulins are under evaluation. Rehabilitative (extraocular muscle or eyelid) surgery is often needed after treatment and inactivation of eye disease. Correction of both hyper- and hypothyroidism is crucial for the ophthalmopathy. Antithyroid drugs and thyroidectomy do not influence the course of the ophthalmopathy, whereas radioiodine treatment may cause the progression of preexisting ophthalmopathy, especially in smokers. The exacerbation, however, is prevented by glucocorticoids. In addition, thyroid ablation may prove beneficial for the ophthalmopathy in view of the pathogenetic model relating eye disease to autoimmune reactions directed against antigens shared by the thyroid and the orbit.