Use of monoclonal antibodies to investigate a possible role of thyroglobulin in the pathogenesis of Graves' ophthalmopathy.

One possible mechanism for Graves' ophthalmopathy is that the progressive orbital inflammation is initiated by formation of thyroglobulin (Tg)-anti-Tg immune complexes at sites of Tg binding to extraocular muscle membranes. In this study monoclonal antibodies (MCAB) against human Tg were used as probes (1) to identify Tg in eye muscle membranes prepared from normal subjects and (2) to measure binding of human Tg and Tg-anti-Tg immune complexes to eye muscle membranes. Reactivity of anti-Tg MCAB with Tg, thyroid, and eye muscle membranes was determined by binding of [125I]anti-Tg monoclonal antibody, an enzyme-linked immunosorbent assay (ELISA), and the indirect immunofluorescence technique. Seven membrane fractions, prepared by differential sucrose gradient centrifugation, were used. Whereas [125I]anti-Tg MCAB bound to all thyroid membrane fractions tested, no [125I]anti-Tg bound to eye muscle membranes. Similarly, reactivity of anti-Tg MCAB with eye muscle membranes was not demonstrated in ELISA or immunofluorescence tests. Although Tg-anti-Tg immune complexes bound to thyroid membranes, such complexes did not bind to eye muscle membranes. Significant binding of [125I]human Tg to eye muscle or thyroid membranes was not demonstrated for any membrane preparation. On the other hand moderate, but significant, binding to skeletal muscle was shown. Similar results were found using an ELISA. Binding of [125I]anti-Tg-Tg complexes of [125I]Tg to thyroid and eye muscle membranes was not affected by the presence of normal human serum, phosphate ions, pH, or incubation temperature, conditions claimed by others to be critical for Tg and Tg-anti-Tg immune complex binding. Since Tg is not present in normal human eye muscle a major role of Tg, or Tg-anti-Tg immune complexes, in the pathogenesis of Graves' ophthalmopathy appears to have been excluded by these findings.