T cell lines from systemic sclerosis patients and healthy controls recognize multiple epitopes on DNA topoisomerase I

Anti-DNA topoisomerase I (topo-I) antibodies are exclusively detected in patients with systemic sclerosis (SSc). Participation of this topo-I-specific autoimmune response in the pathogenesis of SSc has been actively investigated, but remains unproven. Here we characterized the peripheral T cell proliferative response to recombinant topo-I (rtopo-I) in 16 SSc patients with circulating anti-topo-I antibody. A low level (cpm < 2000) T cell proliferation (SI > 3) was detected in 6 (38%) of 16 patients. This low level response was similar to those previously observed in healthy controls. We established 56 topo-I-specific T cell lines recognizing 13 distinct T cell epitopes on topo-I from 4 SSc patients and 2 healthy controls. These T cell lines were established from in vitro activated PBMC (CD25+) by rtopo-I antigen. However they did not have the phenotype of regulatory T cells. Notably, 40 (71%) of the 56 T cell lines recognizing a common epitope were established from one patient. DNA sequencing of the T cell receptor cDNA produced an identical sequence indicating these T cells were from a single topo-I-specific T cell precursor. These results suggest that topo-I-specific T cells can become clonally expanded in some patients and may contribute to the pathogenesis of this disease.