IDENTIFICATION OF A MAJOR PATHOGENIC EPITOPE IN THE HUMAN IRBP MOLECULE RECOGNIZED BY MICE OF THE H-2(R) HAPLOTYPE

Purpose. Mice of the H-2(b), H-2(k), and H-2(r) haplotypes develop exp erimental autoimmune uveoretinitis (EAU) after immunization with inter photoreceptor retinoid-binding protein (IRBP) of bovine or monkey orig in. The purpose of this study was to identify putative pathogenic epit ope(s) of IRBP and to establish their immunodominance within the IRBP molecule. Methods. Overlapping 20-amino acid peptides, spanning the en tire human IRBP molecule, were synthesized and used to immunize C57BL/ 10 (H-2(b)), B10.BR (H-2(k)), and B10.RIII (H-2(r)) mice. Bovine IRBP was used as a positive control. Experimental autoimmune uveoretinitis was examined by histopathology 21 days after immunization. Immunologic responses were assessed by delayed-type hypersensitivity (DH) and lym phocyte proliferation assays. Results. Peptide 161-180, spanning the s equence SGIPYIISYLHPGNTILHVD, was found to be highly pathogenic for B1 0.RIII mice but not for the other strains. A dose-response curve showe d that peptide 161-180 was maximally pathogenic at 50 mu g, but incide nce and scores were reduced at 10 mu g. The truncated 13-mer 165-177 w as also highly pathogenic (100 to 200 mu g), suggesting that it contai ned the pathogenic epitope. Mice immunized with the peptide, or with w hole IRBP, had positive DH and lymphocyte responses to the immunizing as well as to the reciprocal antigen. A cell line derived to peptide 1 61-180 was also pathogenic for B10.RIII mice after adoptive transfer a nd responded (proliferation) to native IRBP. Conclusions. High inciden ce and high severity scores, as well as immunologic cross-recognition of peptide 161-180 and native IRBP in vivo and in vitro, suggest that this peptide contains a major epitope recognized as pathogenic by B10. RIII mice.