Purpose: Paracrine/autocrine interactions between orbital fibroblasts (OF) and infiltrating lymphocytes/macrophages are thought to play a central role in the evolution of Graves' ophthalmopathy (GO). Compounds capable of stimulating the proliferation and synthetic capacities of OF may be of particular importance to these processes, because fibroblasts are known to both produce and respond to certain paracrine factors.
Methods: The effects of interleukin-1 alpha, interleukin-2, interleukin-4, interleukin-6, insulin-like growth factor I, transforming growth factor beta, and platelet-derived growth factor on OF monolayers derived from orbital fatty connective tissue and extraocular muscle endomysium of patients with severe GO undergoing orbital decompression (n = 3), and from connective tissue of normal persons (n = 3) were investigated. Stimulation of proliferation in growth-arrested OF was determined using immunocytochemical staining for the cell-proliferation-related nuclear antigen recognized by a monoclonal anti-Ki 67 antibody. In addition, the effects of OF coincubation with one of the aforementioned compounds and hydrocortisone (10(-7) M), the selective glucocorticoid receptor agonist RU 28362 (10(-7) M), or the glucocorticoid receptor antagonist RU 38486 (10(-7) M) were assessed.
Results: Under baseline conditions (0.1% fetal bovine serum), the proportion of proliferating cells was significantly higher in GO-OF compared with normal OF (p < 0.001). Significant stimulation of GO-OF proliferation was observed with interleukin-1 alpha (10 U/ml), interleukin-4 (1 ng/ml), insulin-like growth factor I (10 ng/ml), transforming growth factor beta (10 ng/ml), platelet-derived growth factor (1 ng/ml), and 1% or 15% fetal bovine serum (all P < 0.01), but not with interleukin-2 (10 U/ml) and interleukin-6 (100 U/ml). Compared with GO-OF, proliferation of normal OF was stimulated by fetal bovine serum to a similar degree, by interleukin-4, insulin-like growth factor I, transforming growth factor beta, and platelet-derived growth factor to a significantly lesser degree (all P < 0.01), and was unaffected by interleukin-1 alpha, interleukin-2, and interleukin-6. Compared with normal OF, either glucocorticoid receptor agonists, but not testosterone or progesterone, specifically inhibited the cytokine-stimulated proliferation of GO-OF to a significantly greater degree (P < 0.01).
Conclusions: The enhanced proliferative capacity of GO-OF at baseline and in response to certain cytokines could play a role in the evolution of the clinical manifestations in GO. Inhibition of cytokine-activated cellular functions may be one mechanism by which glucocorticosteroids exert clinically useful effects in GO.