Activation of OX40 prolongs and exacerbates autoimmune experimental uveitis

Purpose. T cells are essential for the development of autoimmune uveitis. Although the costimulatory molecule OX40 promotes T-cell function and expansion, it is unclear whether OX40 is implicated in ocular inflammation. The purpose of this study was to examine the role of OX40 in uveitis. Methods. Experimental autoimmune uveitis (EAU) was induced in B10.RIII mice by subcutaneous injection of interphotoreceptor retinoid-binding protein peptide 161-180 (IRBP _161-180). Some mice received an intravenous administration of OX40-activating antibody on days 0 and 4 after IRBP161-180 sensitization or on days 10 and 14 of uveitis onset. The severity of EAU was evaluated by histology at different time points. In addition, ocular inflammatory cytokine expression was determined by real time-PCR, and peripheral activated CD4 ⁺CD44 ⁺CD62L ^- T cells and IL-7Rα expression were analyzed by flow cytometry. The activated CD4 ⁺CD44 ⁺ lymphocytes were rechallenged with IRBP _161-180 in vitro to assess their antigen recall response. Results. The authors demonstrated a marked OX40 expression by infiltrating lymphocytes in enucleated human eyes with end-stage inflammation. In addition, the administration of OX40-activating antibody prolonged and exacerbated the disease course of EAU. Moreover, activation of OX40 not only increased CD4 ⁺CD44 ⁺CD62L ^- lymphocyte number, it upregulated IL-7Rα expression in the activated T-cell population. Lastly, these cells exhibited a stronger interferon-γ response to IRBP _161-180 restimulation in vitro. Conclusions. The results reveal a pathogenic role of OX40 in uveitis. Furthermore, the upregulation of IL-7R in CD4 ⁺CD44 ⁺ lymphocytes suggests that the activation of OX40 promotes the generation or expansion of uveitogenic memory T cells.