Anti-muscle antibodies in Graves' ophthalmopathy

The nature of the humoral immune response in patients with Graves' ophthalmopathy has been investigated using a solid phase 125I Protein A binding assay. Retro-orbital muscle (R.O.M.), skeletal muscle (Sk.M.), R.O.M.-membranes, thyroid, kidney, liver, harderian gland, acetylcholine receptors (AchR), actin and myosin were used as target antigens. No significant difference in antibody binding profile to R.O.M. and Sk.M. was found indicating that the ophthalmic immunoglobulins (OIgs) were not recognising a R.O.M. specific antigen(s). Comparison between R.O.M. and R.O.M.-membranes, however, revealed that these antigens were detecting very different antibody populations. Using the former, it appeared that the predominant antibody population being measured was anti-myosin whereas the latter appeared to be detecting primarily anti-AchR antibodies. Anti-actin antibodies were also present in some of the sera. Thus a spectrum of anti-R.O.M. antibodies appears to be present in Graves' ophthalmopathy but the cross-reactivity of these with non-R.O.M. skeletal muscle and their similarity to those found in myasthenia gravis prevent them as yet being used to explain the specific immunopathology observed in this disease.