Characterization of cytokines associated with Th17 cells in the eyes of horses with recurrent uveitis

OBJECTIVE: Equine recurrent uveitis (ERU) is a spontaneous disease that is the most common cause of blindness in horses, affecting up to 15% of the horse population. Th17 cells are a major cell population driving the pathogenesis in several mouse models of autoimmune inflammation, including experimental autoimmune uveitis. The purpose of this study is to investigate the role a Th17 cell-mediated response plays in the pathogenesis of ERU. PROCEDURE: Banked, Davidson's-fixed equine globes histopathologically diagnosed with ERU (n = 7) were compared immunohistochemically with healthy control globes (n = 7). Immunohistochemical staining was performed using a pan-Leptospira antibody and antibodies against IL-6, IL-17, and IL-23. Additionally, immunostaining was performed for T-cell (CD3) and B-cell (CD79α) markers. Specificity of immunoreactivity was confirmed by western blot analysis. RESULTS: Immunohistochemical staining was positive for IL-6, IL-17, and IL-23 within the cytoplasm of nonpigmented ciliary epithelial cells and mononuclear inflammatory cells infiltrating the iris, and ciliary body of ERU horses (n = 7) but negative in controls (n = 7). ERU-affected eyes were CD3 positive (n = 7) and CD79α negative (n = 7). Staining for Leptospira was negative in all ERU and control globes. CONCLUSIONS: Strong immunoreactivity for IL-6, IL-17, and IL-23, in conjunction with the fact that T lymphocytes are the predominating inflammatory cells present in ERU, suggests that IL-17-secreting helper T-cells play a role in the pathogenesis of ERU. These findings suggest that horses with ERU may serve as a naturally occurring animal model for autoimmune uveitis.