ROLE OF RETINAL-PIGMENT EPITHELIUM IN THE DEVELOPMENT OF EXPERIMENTALAUTOIMMUNE UVEITIS

Purpose. To determine the role of retinal pigment epithelium in the in duction of S-antigen-induced uveitis by administration of sodium iodat e (NaIO3) to selectively damage the retinal pigment epithelium. Method s. Forty-four Lewis rats were injected with 60 mu g of S antigen in co mplete Freund's adjuvant. On postimmunization day 9 the rats were sepa rated into four groups: three groups received NaIO3 at doses of 50, 25 , and 10 mg/kg body weight, respectively, and the fourth group (contro l) received diluent. In addition, separate groups of animals (three in each group) received various doses of NaIO3 or diluent. All of the an imals were killed on day 6 after NaIO3 injection, and the eyes were en ucleated and submitted for light and electron microscopic examination. In addition, two groups of Lewis rats (6 in each group) were immunize d with 0.5 ml of guinea pig spinal cord homogenate in complete Freund' s adjuvant to induce experimental allergic encephalomyelitis. On posti mmunization day 7, one group received NaIO3 at a dose of 50 mg/kg body weight, whereas the other group received diluent. All animals were ki lled between days 12 and 14, and spinal cord sections were obtained fo r microscopic examination. Results. In the control group immunized wit h S antigen, severe (2+ to 4+) uveoretinitis developed in 70% of the a nimals. In contrast, only 18% of the animals injected with NaIO3 at a dose of 50 mg/kg body weight exhibited disease, and this was a mild (1 +) form. The groups injected with 25 mg/kg (1+ to 2+) and with 10 mg/k g ((2+ to 3+) of NaIO3 showed a mild to moderate degree of uveoretinit is in 27% and 50% of the animals, respectively. In the remainder of th e animals there was no evidence of uveoretinitis. All of the NaIO3-tre ated animals showed selective necrosis of the retinal pigment epitheli um; this was extensive in the higher dose group and focal in the lower dose groups. In the experimental allergic encephalomyelitis model the re was no significant difference in incidence or histologic appearance of demyelinating disease in NaIO3- vs diluent-treated groups. Conclus ions. These results indicate that the retinal pigment epithelium may p lay a role in the initiation and perpetuation of uveitis after sensiti zation with S antigen. The effect of NaIO3 appears to be localized to the retinal pigment epithelium; it had no effect on immune reactive ce lls, as evidenced by the development of experimental allergic encephal omyelitis in animals treated with NaIO3.