HIGHLY RESTRICTED TCR-ALPHA-BETA USAGE BY AUTOREACTIVE HUMAN T-CELL CLONES SPECIFIC FOR DNA TOPOISOMERASE-I - RECOGNITION OF AN IMMUNODOMINANT EPITOPE

Autoantibody responses to DNA topoisomerase I (Topo I) are highly spec ific to patients with systemic sclerosis (SSc), We recently demonstrat ed that Topo I-specific T cells are components of the T cell repertoir e of patients with SSc and healthy individuals. These autoreactive T c ells were essential for the Ag-specific activation of B cells resultin g in anti-Topo I Ab production in vitro and therefore are believed to play a central role in autoantibody production, To characterize the To po I-specific T cell, 15 T cell clones reactive with Topo I were gener ated from two patients with SSc and three healthy donors, all of whom shared the MHC class II allele DR11. All clones expressed a CD3(+)CD4( +)CD8(-) phenotype and were restricted by HLA-DR, When eight rTopo I f ragments were tested individually as Ags, all clones responded to F5, which encodes amino acids 209 through 386 of Topo I, but not to F10, w hich encodes amino acids 209 through 276, indicating that one or more immunodominant epitopes on Topo I is located between amino acids 276 a nd 386. Analysis of TCR gene usage showed that the predominant V alpha segment of the functionally rearranged TCR-alpha gene was V delta 5, which was used by seven clones, Most strikingly, all except one T cell clone had functional rearrangements of TCR beta-chain genes using the V beta 20.1a and J beta 1.1 gene segments, Comparison of the CDR3 seq uences of the TCRs revealed limited diversity, and, of note, all clone s contained the amino acid motif PGGN (or minor variations) in the CDR 3 of their TCR beta-chains. Furthermore, identical beta-chain CDR3 ami no acid sequences were encoded by cDNAs generated from T cell clones d erived from multiple individuals, including patients with SSc and heal thy donors.