Experimental autoimmune retinitis in the rat induced by immunization with rhodopsin: an ultrastructural study

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.

Experimental autoimmune anterior uveitis (EAAU). II. Dose-dependent induction and adoptive transfer using a melanin-bound antigen of the retinal pigment epithelium

Retinal pigment epithelial cell fractions have been investigated for their capacity to induce experimental uveitis. Cells of the dark (melanotic) and light areas of the bovine RPE have subsequently been extracted by buffer, Triton X-100, sodium dodecyl sulfate (SDS), and treated with various reagents in order to study some characteristics of the antigen. The SDS-insoluble melanotic fraction, consisting of spindle-shaped, mature melanin granules, proved to be the most uveitogenic preparation. Using pertussis toxin as coadjuvant, 1 microgram of melanin-protein (3.4 x 10(6) granules) was able to induce experimental autoimmune anterior uveitis (EAAU) in Lewis rats. The pathogenic activity of the responsible pathogen (PEP-X) was not diminished by SDS, nor eliminated by mildly alkaline SDS or formic acid treatment. However, HCl-deproteinized granules were not uveitogenic. The results show that PEP-X is a highly stable melano-antigen that is probably covalently bound to the granule surface. This is the first time that a melanin-bound antigen has been demonstrated to evoke specific autoaggressive activity. EAAU could adoptively be transferred by sensitized and in vitro stimulated CD4 T-lymphocytes. The evoked inflammation started 3-4 days after injection, was similar to those induced by immunization, and consisted mainly of severe iridocyclitis accompanied by dense flare and cells in the anterior chamber. Choroiditis developed in severe cases of EAAU but no inflammation was detected in the retina, pineal gland or other organs of these rats. EAAU could not be transferred by serum. Immunized PVG rats and guinea-pigs did not develop ocular inflammation. In monkeys a high dose of antigen evoked a very mild EAAU accompanied by choroiditis. In view of its characteristics, EAAU may be a new model for human anterior uveitis.

Experimental autoimmune posterior uveitis accompanied by epitheloid cell accumulations (EAPU). A new type of experimental ocular disease induced by immunization with PEP-65, a pigment epithelial polypeptide preparation

Purified retinal pigment epithelial cells of bovine eyes have been fractionated by a series of buffer and detergent extractions. The electropherogram of the buffer-insoluble, Triton X-100-soluble fraction (RPE-TS) exhibits a major polypeptide band of M(r) 65 kDa and a variety of minor components. Electrophoretically purified 65 kDa-band protein (PEP-65) is immunologically unrelated to the known uveitogenic photoreceptor proteins, to other neural retina proteins, and to PEP-X, the RPE-melanin-bound uveitogenic antigen. An immunocytochemical study of eye tissues suggests that it is exclusively located in the RPE. Immunization of Lewis rats with PEP-65 or affinity-purified RPE-TS induces a new type of ocular disease: experimental autoimmune posterior uveitis accompanied by epitheloid cell accumulations (monocytes) adjacent to the RPE (EAPU). The disease starts 9 days after immunization, provided that pertussis toxin is used as co-adjuvant. The first clinical signs are transient flare and cells in the anterior chamber. Choroiditis develops, and epitheloid cells accumulate focally along one or both sides of the Bruch's membrane-RPE layer. Such foci resemble, in some respects, Dálen-Fuchs nodules which occur in human sympathetic ophthalmia. Areas of inflammation are frequently localized in the chorioretinal periphery adjacent to the pars plana. Vitreous cell infiltration is the most prominent clinical feature of EAPU. During at least 2 months, extending chorioretinal areas containing epitheloid cell collections remain while the adjacent photoreceptor cells sometimes disappear without being invaded by these cells. Retinal vasculitis is seldomly observed and pinealitis is absent. EAPU has the latter feature in common with PEP-X-induced experimental autoimmune anterior uveitis (EAAU). The two diseases differ from the various photoreceptor antigen-induced forms of EAU where pinealitis and inflammation of the neural retina are prominent features. However, just as in EAU and EAAU, EAPU can be adoptively transferred, and is inhibited by cyclosporin treatment suggesting T-cell dependency.