Characterization of Clinical and Immune Responses in an Experimental Chronic Autoimmune Uveitis Model

Autoimmune uveitis is a sight-threatening intraocular inflammatory disease. For >30 years, the mouse model of experimental autoimmune uveitis has been employed to investigate disease mechanisms and test immunotherapeutic approaches. However, inflammation in this model is self-limited, and does not replicate the chronic, insidious nature prevalent in the human disease. Herein, a robust and reliable model of chronic autoimmune uveitis was developed and characterized in two strains of wild-type mice by modifying interphotoreceptor retinoid-binding protein dose and peptide fragments from conventional experimental autoimmune uveitis models. In both of these murine strains, immunization with our modified protocols resulted in a slowly progressive uveitis, with retinal scars and atrophy observed in the chronic stage by fundoscopy. Optical coherence tomography demonstrated decreased retinal thickness in chronic autoimmune uveitis mice, and electroretinography showed significantly reduced amplitudes of dark-adapted a- and b-waves and light-adapted b-waves. Histologic examination revealed prominent choroiditis with extensive retinal damage. Flow cytometry analysis showed substantially increased numbers of CD44^hiIL-17⁺IFN-γ⁻ memory T-helper 17 (Th17) cells in the retina, cervical lymph nodes, inguinal lymph nodes, and spleen. These data establish new modified protocols for inducing chronic uveitis in wild-type mice, and demonstrate a predominant memory Th17 cell response, suggesting an important role for memory Th17 cells in driving chronic inflammation in autoimmune uveitis.

Uveitis is a sight-threatening inflammatory condition of the uveal tract of the eye, comprising the iris, ciliary body, and choroid.¹ Responsible for an estimated 30,000 new cases of legal blindness each year in the United States, uveitis and its complications cause approximately 10% of irreversible vision loss.2, 3, 4, 5 The socioeconomic impact of uveitis is notable because as blindness frequently occurs in individuals of working age.⁶ In contrast to acute uveitis, which often resolves after a short course of topical corticosteroids, chronic uveitis is characterized by active inflammation that persists for at least several months, and frequently years. The persistent inflammation and its long-term requirement for corticosteroids lead to a high incidence of complications that endanger vision, including glaucoma, cataract, optic disc atrophy, and chorioretinal scars.⁷Experimental animal models have been used to recapitulate the clinical phenotype of uveitis, and have led to significant advances in our understanding of the cellular and molecular mechanisms that cause autoimmune uveitis.⁸ For example, these studies have established the critical roles of pathogenic effector T-helper 1 (Th1) and T-helper 17 (Th17) cells in the immunopathogenesis of uveitis.8, 9, 10 However, most preclinical research on autoimmune uveitis has investigated acute disease, but not the development and maintenance of chronic autoimmune uveitis (CAU).¹¹ This is because, in the widely used mouse experimental autoimmune uveitis (EAU) model, disease peaks in the first 2 to 3 weeks after immunization before resolving spontaneously.12, 13, 14, 15 Yet, as discussed, it is CAU that is associated with the greatest morbidity and risk of sight-threatening complications in the clinic, underscoring a pressing need for the development of a chronic uveitis animal model.⁷In the present study, a reliable murine model of chronic experimental autoimmune uveitis was established and characterized in two wild-type mouse strains, which exhibit clinical features consistent with noninfectious uveitis observed in humans. Furthermore, in contrast to early acute uveitis in which the immune response is characterized by both effector Th1 and effector Th17 cells, we demonstrate that CAU is primarily characterized by a robust memory Th17 response in both the retina and peripheral lymphoid compartments.