Autoimmune endocrine ophthalmopathy and retrobulbar antigens

Endocrine Ophthalmopathy (EO) is based on autoimmune processes that lead to lymphocyte infiltration of the retrobulbar space. In this study, antigenic character of retrobulbar adipose, connective and muscle tissue as well as of cultured fibroblasts and myoblasts were examined. Samples were obtained from EO patients (n = 13, 8 fem., age 26-82 years, median 47 years) undergoing orbital decompression surgery. Retrobulbar and abdominal tissue from 7 controls (4 fem., 48 - 74 y) was investigated, too. Tissues were homogenized and the proteins were separated by SDS-PAGE according to molecular weight. In order to recover the separated proteins in soluble form, an electroelution technique was employed. Twenty-two separated soluble protein fractions were used as antigenic stimuli for autologous peripheral blood mononuclear cells (PBMC) separated by Ficoll gradient centrifugation. Subsequently, the proliferation of T cells was measured by [3H]-thymidine uptake. A marked T cell response to protein fractions with molecular weight of 6 - 10 kD and 19 - 26 kD was detected (p < 0.001). These autoantigens were found readily reproducible in adipose tissue in 8 out of 9 EO patients, stimulation index (SI) to antigen 6 - 10 kD 29 +/- 4.6 (mean +/- SEM); 19 - 26 kD 5 +/- 1.4 and in 3 out of 4 patients using retrobulbar eye muscle tissue (SI: 6 - 10 kD 23 +/- 4.2; 19 - 26 kD 6 +/- 2). Using the proteins of cultured fibroblasts as antigen, the autologous PBMC from 2 out of 4 tested EO-patients also responded (SI: 7 +/- 2; 4 +/- 1.4). Testing cultured retrobulbar myoblasts of an EO patient, a response to the 19 - 26 kD antigen was found only (SI: 8.0). In response to retrobulbar or muscle proteins, PBMC of 2 controls showed also a higher proliferation rate (SI: 16 +/- 3.5; 13 +/- 2.8), whereas, a response to abdominal adipose or muscle proteins (4 controls) was never found. Thus, two orbital antigens reacting with autologous T cells could be demonstrated and may play an important role in the immunopathogenesis of EO. According to these findings, retrobulbar fibroblast antigens are most likely the main T cell targets.