Multiple, spatially distinct T cell epitopes within a pathogenic 123 residue cyanogen bromide peptide of bovine retinal S-antigen

Abstract

We have examined the T cell specificity of a Lewis rat T cell line (R208) specific for a pathogenic, 123 residue cyanogen bromide produced peptide of bovine S-antigen by using two independent sets of overlapping synthetic peptides representing the entire length of the 123 residue fragment. S-antigen, a 48 kDa immunopathogenic photoreceptor cell autoantigen induces T cell mediated experimental autoimmune uveoretinitis (EAU) in experimental animals. Extensive analyses revealed a heterogenous response by the R208 line to the panel of synthetic peptides, proliferating weakly to 4 distinct sites. Unexpectedly, peptides representing sequences (residues 286 – 297 and 303 – 320 of bovine S-antigen) known to actively induce the autoimmune pathology were unable to significantly stimulate the R208 line as assessed by proliferation assays. Similarly, attempts to isolate T cells specific for these sequences from the R208 line have proven unsuccessful. However, two sequences, residues 253 – 269 and 273–289, sufficiently stimulated R208 cells to allow isolation of sub-lines, R208:26 and R208:28, respectively. Neither of these peptides actively induce an autoimmune response. R208:26 does not transfer EAU and R208:28 transfers moderate EAU. As a control, we are able to isolate a pathogenic T cell line (R502) specific for the actively pathogenic sequence, residues 303–320, when this peptide is used as the immunogen. However, the R502 line proliferates to peptides (e.g. 305–322) which do not contain residues 303 and 304 which are critical for the active induction of disease. These results show a multiplicity of distinct T cell epitopes within a relatively small region of S-antigen. Furthermore, there appears to be a dissociation between proliferative sites and pathogenic sites. A partial amino acid sequence (through the 123 residue region) of rat retinal S-antigen predicted from cDNA clone RT.A11 is also reported to show sequence disparities in the region.