Thyrotropin Receptor and CD40 Mediate Interleukin-8 Expression in Fibrocytes: Implications for Thyroid-Associated Ophthalmopathy (An American Ophthalmological Society Thesis)

Purpose: To better understand the pathogenesis of thyroid-associated orbitopathy (TAO) through elucidating the role of thyrotropin receptor(TSHR) and CD40in the expression of interleukin-8(IL-8) in peripheralblood fibrocytes. Fibrocytesinfiltrate the orbit of patients with TAO, where they differentiate into fibroblasts. Fibrocyteprecursors occur with increased frequency in the peripheralblood expressing TSHR and CD40in TAO patients. We hypothesize that in vitro derived fibrocytesand peripheralblood fibrocyteprecursors express proinflammatory chemoattractant molecules including IL-8 initiated by TSHR and CD40signaling. Since nearly all TAO patients express activating antibodies to TSHR, this is particularly relevant for activation of peripheralblood fibrocytes. Methods: TSHR and CD40expression on peripheralblood fibrocyteswas determined by flow cytometry. IL-8 RNA was quantitated by real-time polymerase chain reaction. IL-8 protein production was measured by Luminex and flow cytometry. Thyroid-stimulating hormoneand CD40ligand–stimulated phosphorylation of Akt in peripheralblood fibrocyteswas studied by flow cytometry. Results: Both TSHR- and CD40-mediated signaling lead to IL-8 expression in mature fibrocytes. Fibrocyteprecursors assayed directly from circulating peripheralblood demonstrate intracellular IL-8 expression with addition of thyroid-stimulating hormoneor CD40ligand. TSHR- and CD40-induced IL-8 production is mediated by Akt phosphorylation. Conclusions: Peripheralblood TSHR+ and CD40+ fibrocytesexpress IL-8 and may promote the recruitment of inflammatory cells, mitogenesis, and tissue remodelingin TAO. TSHR- and CD40-mediated IL-8 signaling is mediated by Akt. Delineating the molecular mechanisms of fibrocyteimmune function may provide potential therapeutic targets for TAO.