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Objectives: This study is aimed at determining the role of T cells by assessing the numbers of IFN-γ- and IL-2-secreting T cells following stimulation with peptides derived from DNA topoisomerase-I protein in Thai SSc patients.Methods: Fifty Thai SSc patients and 50 healthy controls (HC) joined this study. IFN-γ and IL-2 levels upon stimulation of T cells with 6 peptides derived from DNA topoisomerase-I protein were determined. Anti-nuclear antibodies (ANA) and anti-Scl-70 antibodies were determined by using the ELISA method.Results: In SSc patients, we detected a significantly higher number of IFN-γ- and IL-2-secreting CD8+ T cells than IFN-γ- and IL-2-secreting CD4+ T cells after stimulation with pooled peptides derived from DNA topoisomerase-I protein. A similar percentage of CD4+IL-2+, CD4+IFN-γ+, and CD8+IL-2+ were detected following stimulation with DNA topoisomerase-I protein -in SSc patients with anti-Scl-70 antibody (SSc/anti-Scl-70+) and those without. In contrast, the amount of CD8+IFN-γ+ cells was significantly higher in SSc/anti-Scl-70+ than those without. Stimulation with individual peptides showed that CSLRVEHINLHPELD (sPep3; 15 amino acids; position 505-519 of DNA topoisomerase-I protein) was the optimal epitope that induced T cells secreting the highest levels of IFN-γ and IL-2. A higher percentage of IFN-γ+CD4+ T cells was detected in SSc/anti-Scl-70+ than those without the following stimulation with peptides 2 (amino acid position 475-486 [RAVALYFIDKLA] of protein DNA topoisomerase).Conclusion: The results from this study emphasize the critical role of DNA topoisomerase-I peptides on the activation of T cells in SSc patients. The findings provide a better understanding of SSc's immunopathogenesis and may lead to the development of diagnostic tools and specific treatments for SSc in the future. [ABSTRACT FROM AUTHOR]