ABSTRACT
The specific adaptive immune response can, in rare instances, be mounted against self antigens and cause autoimmune disease. Injury to body tissues can result from antibodies directed against cell-surface or extracellularmatrix molecules, from antibodies bound to molecules circulating in the plasma that deposit as immune complexes, or from clones of T cells that are reactive with self antigens. A special class of autoimmune diseases are caused by autoantibodies to cell-surface receptors (Fig. 40.1). Graves’ disease and myasthenia gravis are two well-studied examples. Graves’ disease is caused by autoantibodies to the receptor on thyroid cells for thyroid-stimulating hormone (TSH), secreted by the pituitary gland. In this disease, the binding of the autoantibody to the TSH receptor acts like TSH itself, and stimulates the thyroid gland to produce thyroid hormones. In myasthenia gravis, the opposite effect is observed: antibodies to the acetylcholine receptor at the neuromuscular junction impede the binding of acetylcholine and stimulate internalization of the receptor, thereby blocking the transmission of nerve impulses by acetylcholine (Fig. 40.2).
