Affinity purification of orbital membrane antigens for the study of the pathogenesis of Graves' ophthalmopathy

Abstract

We characterized 22 human monoclonal antibodies (MCAB) reactive with human orbital antigens. Most of these monoclonal antibodies had variable degrees of reactivity with eye muscle, orbital connective tissue, thyroid, and extra-thyroid tissue preparations when tested in an enzyme-linked immunosorbent assay (ELISA). Eight of the MCABs, selected on the basis of their reactivity with human eye muscle or orbital connective tissue antigens, were used to affinity purify orbital membrane antigens. All purified fractions were tested in the ELISA for reactivity with the MCAB used for their purification. Four of the purified antigens with a high reactivity were not proteins. To increase the specificity of the reactivity of serum autoantibodies with affinity-purified antigens, we developed a competitive binding ELISA in which the MCAB-immunoglobulin was directly labeled with alkaline phosphatase. We tested the serum of 24 patients with Graves' ophthalmopathy, 10 patients with a history of Graves' hyperthyroidism and no eye disease, 14 patients with Hashimoto's thyroiditis without eye disease, 8 patients with other nonautoimmune thyroid disorders, and 20 normal subjects for reactivity with an affinity-purified nonprotein orbital antigen. The levels of serum autoantibodies against this antigen in patients with Graves' ophthalmopathy were significantly higher than those in normal subjects or patients with Graves' hyperthyroidism with no eye disease. Although unlikely to be of primary pathogenetic significance, it is possible that levels of this antibody in patients with Graves' ophthalmopathy may reflect the extent of orbital inflammation and, therefore, be useful as a clinical marker.