IMMUNOGLOBULIN CLASS AND SUBCLASS DISTRIBUTION OF EYE MUSCLE AND FIBROBLAST ANTIBODIES IN PATIENTS WITH THYROID-ASSOCIATED OPHTHALMOPATHY

OBJECTIVE The investigation of the antibody response in thyroid-associ ated ophthalmopathy (TAO) using different antigens and assays has give n inconsistent results. We have analysed antibodies against eye muscle and control antigens in a large group of TAO patients to assess wheth er specific eye muscle antibodies exist in TAO. We have also evaluated the presence of IgA and IgM class antibodies and examined IgG subclas s distribution. DESIGN Sera were obtained from all patients (TAO, Grav es' disease without ophthalmopathy and Hashimoto's thyroiditis) within one year of diagnosis. Sera were also collected from healthy controls , with no family history of autoimmune thyroid disease. PATIENTS Thirt y-eight patients had Graves' disease with Grade III or greater TAO; 15 patients had Graves' disease without ophthalmopathy and nine had Hash imoto's thyroiditis without any eye signs. The control group consisted of 14 subjects. MEASUREMENTS Antibodies against porcine eye and skele tal muscle, human eye (membrane and soluble antigen) and skeletal musc le, human thyroid microsomal and thyroglobulin antigens and dermal and orbital fibroblast antigens were assessed using ELISA. Antibody isoty pes and IgG subclasses were studied for porcine and human eye muscle a ntibodies. Eye muscle (porcine and human) and orbital fibroblast antib odies were further analysed by immunoblotting. RESULTS There were no s ignificant differences in the ability of either IgG or IgA in sera fro m the different groups to bind porcine and human eye muscle antigens. There was a significant correlation (P < 0.0001) between the binding t o porcine eye muscle and skeletal muscle antigens (for both IgG and Ig A). There was no difference between sera from TAO patients and control subjects in their binding to eye muscle fibroblasts for both IgG and IgA antibodies. However, IgA antibody activity against dermal fibrobla sts differed significantly between TAO patients and controls (P < 0.05 ). By immunoblotting, the frequency of IgA antibodies recognizing 21 k Da (40% of patients) and 62 kDa (52%) bands in porcine eye muscle blot s and 20, 24 and 38 kDa bands in blots of human eye muscle (soluble) a ntigen differed significantly between patients with TAO and controls ( P < 0.05 in all cases). IgG antibodies recognizing 80 and 92 kDa bands in blots of the subcellular membrane antigen prepared from orbital fi broblasts were found more frequently in patients with TAO compared wit h controls (P < 0.05 in both cases). CONCLUSIONS We found no evidence that eye muscle membrane or fibroblast antibodies are present in a sig nificant proportion of TAO patients, using ELISAs based on antigens pr epared from several sources. We have also failed to demonstrate the pr esence of previously described specific, TAO-associated antibodies, in cluding those directed against a 64 kDa protein in eye muscle and a 23 kDa protein in fibroblasts. IgA class antibodies reactive with orbita l components appeared to be more strongly associated with TAO than tho se of the IgG class, though even this relationship is weak. These resu lts suggest that antibodies are of secondary importance in the pathoge nesis of TAO, which is most likely a T cell-mediated disorder.