High Mobility Group Box Protein-1 in Experimental Autoimmune Uveoretinitis

Purpose: To investigate whether high mobility group box protein (HMGB)-1, acting as a novel proinflammatory cytokine, is involved in experimental autoimmune uveoretinitis (EAU).

Methods: HMGB-1 concentration was measured in aqueous humor, and serum was obtained from Lewis rats immunized with interphotoreceptor retinoid binding protein (IRBP) peptide (R14) and complete Freund adjuvant (CFA), rats immunized with CFA, and nontreated rats on day 14 after immunization. Immunofluorescence histochemistry was performed to examine the localization of HMGB-1 and the receptor for advanced glycation end products (RAGEs) in eyes obtained from nontreated rats or EAU-induced rats. Coexpression of CD68 (marker for macrophages) was investigated by double-immunofluorescence labeling.

Results: The level of HMGB-1 in aqueous humor was significantly elevated in eyes with EAU, and HMGB-1 and tumor necrosis factor (TNF)-alpha levels correlated with active ocular inflammation. HMGB-1 was expressed in the iris, ciliary body, and retina of eyes from nontreated rats and EAU-induced rats. Furthermore, HMGB-1 and RAGE were found in inflammatory cells infiltrating the anterior chamber, vitreous cavity, and subretinal space in EAU-induced rats. Some HMGB-1- or RAGE-positive cells in eyes with EAU were CD68(+). Cultured macrophages expressing RAGE released TNF-alpha on stimulation with native HMGB-1.

Conclusions: HMGB-1 was elevated in the aqueous humor of eyes with EAU. Inflammatory cells infiltrating ocular tissue expressed HMGB-1 and RAGE. HMGB-1 has the capacity to stimulate TNF-alpha production in bone marrow-derived macrophages. These results support the possibility that extracellularly released HMGB-1 acts as a novel proinflammatory cytokine to promote and amplify ocular inflammation in autoimmune uveoretinitis.