Retrobulbar adipocytes and humoral immunity in Graves' ophthalmopathy

As CT and MR-imaging revealed an enlargement of retrobulbar fat tissue in patients with Graves' ophthalmopathy, the role of the retrobulbar adipocytes in the pathogenesis of this disorder remains to be elucidated. To evaluate the in vitro influence of humoral immunity on retrobulbar adipose tissue, the effects of IgG and sera from 56 euthyroid ophthalmopathy patients and 53 controls on both porcine and human (patients' and controls') retrobulbar adipocytes were measured by means of several assays: An enzyme-linked immunosorbent assay was employed to reveal specific binding of antibodies to the adipocytes. Metabolic activity was determined by means of a colorimetric dimethyl thiazolium-diphenyl-tetrazolium bromide test which quantifies the activity of mitochondrial dehydrogenases; cell proliferation was measured by incorporation of [3H]-thymidine in 24 h, and activities of adipocyte specific enzymes, such as membrane-bound lipoprotein lipase and 1-glycerol-3-phosphate-dehydrogenase were determined. By means of these specific enzyme tests no distinctions could be made between patients and controls. Furthermore, a significant difference between patients' (untreated and treated) and controls' IgG to bind to, to activate or to stimulate the proliferation of porcine or human (patients' and controls') retrobulbar adipocytes could not be detected under the employed experimental conditions. The effects of patients' heat-inactivated and non-inactivated sera were indistinguishable from those of the controls. Incubation with autologous sera, however, led to an activation of the retrobulbar adipocytes which was higher than the median caused by the patients' group and that engendered by incubation with autologous IgG.(ABSTRACT TRUNCATED AT 250 WORDS)