Elucidation of the amino acid sequences of retinal S-antigens from several species has allowed the fine dissection of T cell and antibody epitopes using synthetic peptides. S-antigen, isolated from retinal rod photoreceptor cells, elicits experimental autoimmune uveoretinitis (EAU), a predominantly CD4+ T-cell mediated autoimmune disease of the retina and uveal tract of the eye and pineal gland. Three uveitogenic T cell lines, R9, R17 and R208, prepared against native bovine S-antigen, human S-antigen and cyanogen bromide peptide CB123, respectively, were used to identify the T cell recognition sites responsible for uveitogenic and proliferative responses. T cell epitopes were found to be clustered into 6 regions, some of which were species-specific. The two synthetic peptides known to actively induce EAU, residues 286-297 and 303-314 of bovine S-antigen, were unable to induce significant proliferative responses in any of the three T cell lines. However, both of these sites were adjacent to synthetic peptides, residues 273-292 and 317-328, respectively, which were unable to actively induce EAU, but elicited proliferative responses from the T cell lines. We also report the presence of a new pathogenic site, also associated with an adjacent proliferative site, together in residues 343-362 of bovine S-Ag. Our results indicate that spatially separate and distinct T cell epitopes are present in S-antigen which are responsible for the active induction of EAU, lymphocyte proliferation, and adoptive transfer of EAU.
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ACKNOWLEDGEMENTS We thank Marcella Isaac for preparing the samples for histology. This work was supported by NIH grants EY-05417 (D.S.G.), EY-05095 (L.A.D.), Research to Prevent Blindness, the Crippled Children's Vitreo-Retinal Research Foundation (L.A.D.), and the Pennsylvania Lions Sight Conservation and Eye Research Foundation (L.A.D.). D.S.G. is a Research to Prevent Blindness Senior Scientific Investigator.