IL-1β Induces IL-6 Expression in Human Orbital Fibroblasts: Identification of an Anatomic-Site Specific Phenotypic Attribute Relevant to Thyroid-Associated Ophthalmopathy

Human orbital fibroblasts exhibit a unique inflammatory phenotype. In the present study, we report that these fibroblasts, when treated with IL-1beta, express high levels of IL-6, a cytokine involved in B cell activation and the regulation of adipocyte metabolism. The magnitude of this induction is considerably greater than that in dermal fibroblasts and involves up-regulation of IL-6 mRNA levels. IL-1beta activates both p38 and ERK 1/2 components of the MAPK pathways. Disrupting these could attenuate the IL-6 induction. The up-regulation involves enhanced IL-6 gene promoter activity and retardation of IL-6 mRNA decay by IL-1beta. Dexamethasone completely blocked the effect of IL-1beta on IL-6 expression. Orbital fibroblasts also express higher levels of IL-6R than do skin-derived cells. When treated with rIL-6 (10 ng/ml), STAT3 is transiently phosphorylated. Thus, the exaggerated capacity of orbital fibroblasts to express high levels of both IL-6 and its receptor in an anatomic site-selective manner could represent an important basis for immune responses localized to the orbit in Graves' disease.