Possible role of human foamy virus in Graves' disease

Human foamy virus (HFV) is a member of the retroviral family of Spumaretrovirinae. In addition to the three retroviral structural genes, gag, pol and env, HFV also contains regulatory sequences, called bel. Foamy viruses have been previously associated with human thyroid disease, notably DeQuervain's thyroiditis. In indirect immunofluorescence tests we have demonstrated the reactivity of the thyroid glands of 7/7 patients with Graves' disease and antibodies to HFV gag proteins. No reactivity was observed with antibodies to pol, env and bel proteins. Nine thyroids of patients with struma parenchymatosa, 4 with follicular carcinoma and 2 normal thyroids were negative throughout. From the thyroids of 5 patients with Hashimoto's disease, 4 were negative and 1 showed a single small focus of anti-gag antibody reactivity. The uniform immunofluorescent staining was restricted to the basal and lateral intercellular areas between the thyroid epithelial cells. Extension of these studies to the retrobulbar tissue of 1 Graves' disease patient with malignant exophthalmus revealed positive staining with anti-gag antibodies of fibroblasts and fat cells but not eye muscles. Furthermore, we were successful in establishing several T-cell lines derived from the retrobulbar tissue of this patient. They were CD8+ and proliferated, in contrast to peripheral blood cells, upon cocultivation with autologous retroorbital fibroblasts. It remains to be determined whether these observations are of relevance in the pathogenesis of Graves' disease.