Autoantibodies reactive with extracellular matrix proteins in patients with thyroid-associated ophthalmopathy

Autoantibodies reacting with extracellular matrix proteins have been extens ively studied in various autoimmune connective tissue diseases. Because of the possibility that such antibodies may play a role in orbital connective tissue inflammation in thyroid-associated ophthalmopathy (TAO), we studied the humoral immune response against specific extracellular matrix (ECM) pro teins, namely: collagen types I, III, IV, V (CI, CIII, CIV, CV), fibronecti n (FN), and laminin (LM). Anti-ECM antibodies of immunoglobulin G (IgG), Ig A, and IgM classes were determined by enzyme linked immunosorbent assay (EL ISA). Overall, sera from 50% of patients with TAO contained antibodies reac tive against one or more ECM proteins, compared to 27% with Graves' disease (GD) without evident eye involvement, 28% with Hashimoto's thyroiditis (HT ), and 9% of normal subjects. Serum anti-CI, anti-CIII, anti-CV and anti-LM levels were significantly (p < 0.05) higher in patients with TAO than in n ormals. Anti-CI, anti-CV and anti-LM reactivity was antigen-specific in mos t TAO sera, while anti-CIII antibodies cross-reacted with other antigens. A nti-collagen antibodies were mainly of the IgG class. To determine the stru ctural epitopes of these proteins, we performed immunoblotting studies on c yanogenbromide (CNBr)-derived peptides of CI and CV, While sera from 9 of 1 0 patients with TAO reacted with CI peptides, the response was polyclonal a nd uniform in all patients. However, only 2 of 10 TAO sera reacted with CV peptides. In conclusion, our study suggests that a variety of ECM proteins (CI, CV, LM) may be secondary autoantigens that are recognized by antibodie s in TAO, While these antibodies appear to react with epitopes expressed on both native and denatured proteins, and may therefore have the potential t o bind to ECM in vivo, their pathogenic role in TAO remains unknown.