Xenopus IRBP, a phylogenetically remote protein, is uveitogenic in Lewis rats

Mammalian interphotoreceptor retinoid-binding proteins (IRBPs) are highly u veitogenic in Lewis rats. Xenopus laevis IRBP resembles mammalian IRBP in i ts four-fold structure, and has similar to 70% amino acid sequence identity with the bovine protein. This study investigated the uveitogenicity of rec ombinant Xenopus IRBP and two of its derived peptides in Le Lewis rats. Rat s immunized with Xenopus IRBP developed uveoretinitis as well as pineal inf lammation. The Xenopus molecule was, however, less immunopathogenic than th e bovine IRBP. Of the two Xenopus IRBP peptides tested, 1180-1191 was remar kably uveitogenic, whereas sequence 521-540 exhibited low activity. It is a ssumed, therefore, that as with bovine IRBP, peptide 1180-1191 is the major uveitogenic sequence in Xenopus IRBP. The role individual residues of thes e peptides play in the immunopathogenic process is discussed. Our data thus demonstrate that despite its being phylogenetically remote, Xenopus IRBP i s uveitogenic in Lewis rats.