Ultrastructural pathology of experimental autoimmune uveitis in the rat.

Experimental autoimmune uveoretinitis (EAU) has been extensively studied as a model for human posterior uveitis, however, few ultrastructural studies of EAU in the rat have been reported. In the present report we document a systematic time-course study of the posterior segment changes in the Lewis rat. The disease varied somewhat in severity in animals sacrificed at identical times after immunisation. In the prodromal stage of the disease, usually around day 14, early pathological changes included mild peripapillary vasculitis and low grade mononuclear and neutrophilic infiltration of the subretinal space with phagocytosis of the rod outer segments. The features of the severe or active diseases were most evident on day 21 and included mixed cellular infiltrate of the vitreous, subretinal serohaemorrhagic exudate, focal retinal detachment and necrosis. Outer retinal destruction was often most severe adjacent areas of retinal vasculitis. Focal monocytic subpigment epithelial microgranulomas, reminiscent of Dalen-Fuch's nodules in humans, were also identified. By day 28 and 49 active inflammation had subsided and large segments of the outer retina were completely destroyed. The retinal pigment epithelium (RPE) also showed signs of activation in the vicinity of focal retinochoroidal mononuclear infiltrates including multilayering, proliferation and increased phagocytosis. Finally, neovascularisation of the RPE by non-fenestrated capillaries derived from the retinal vasculature was evident in the late stages of the disease.