AUTOANTIBODIES TO TYROSINASE-RELATED PROTEIN-1 DETECTED IN THE SERA OF VITILIGO PATIENTS USING A QUANTITATIVE RADIOBINDING ASSAY

In the present study, we describe the in vitro transcription-translati on of human tyrosinase-related protein-1 (TRP-I) cDNA and subsequent u se of the resulting S-35-labelled TRP-1 in a radioimmunoassay to analy se vitiligo sera for the presence of TRP-I antibodies, Of 53 vitiligo sera examined in the assay, three (5.7%) were found to be positive for TRP-1 antibodies. In contrast, sera from. 20 controls, 10 patients wi th Hashimoto's thyroiditis and 10 patients with Graves' disease were a ll negative for TRP-1 antibodies. Although glycosylation of the labell ed protein was necessary for its immunoprecipitation by TRP-l-specific monoclonal antibody TA99, this post-translational processing did not affect the binding of any of the sera tested. All three patients posit ive far TRP-I antibodies (aged 50-63 years) had bad vitiligo of the sy mmetrical type for more than I year, and all of them also had an assoc iated autoimmune disorder: Graves' disease in one and autoimmune hypot hyroidism in two. Tn addition, antibodies to the melanogenic enzymes t yrosinase and tyrosinase-related protein-2 (TRP-2) were present in the ir serum. Absorption studies indicated that preincubation with COS-7 c ell extract containing either expressed TRP-1, tyrosinase or TRP-2 abs orbed out the immunoreactivity of the three sera positive in the radio immunoassay (RIA) with [S-35]TRP-1. The results indicate that autoanti bodies to TRP-I cross-react with tyrosinase and TRP-2, suggesting one or more common epitopes between the three proteins.