Research Article Determination of T Cell Responses in Thai Systemic Sclerosis Patients Oranit Likhit, 1 Worawit Louthrenoo, 2 Sa-nga Pattanakitsakul, 3 Aroonrung Suttitheptumrong, 3 Supot Hannongbua, 4 Thanyada Rungrotmongkol, 5,6 Hiroshi Noguchi, 7,8 Fujio Takeuchi, 8 and Kobporn Boonnak 9 1 Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok 10400, Thailand 2 Division of Rheumatology, Department of Internal Medicine, Faculty of Medicine, Chiang Mai University, 50200, Thailand 3 Division of Molecular Medicine, Research Department, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand 4 The Center of Excellence in Computational Chemistry, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand 5 Biocatalyst and Environmental Biotechnology Research Unit, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand 6 Program in Bioinformatics and Computational Biology, Graduate School, Chulalongkorn University, Bangkok 10330, Thailand 7 School of Pharmacy, Nihon Pharmaceutical University, Saitama 361-0806, Japan 8 School of Pharmaceutical Science, University of Shizuoka, Shizuoka 422-8526, Japan 9 Department of Immunology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand Correspondence should be addressed to Kobporn Boonnak; kobporn.boo@mahidol.edu Received 10 December 2021; Revised 12 February 2022; Accepted 21 February 2022; Published 7 March 2022 Academic Editor: Baohui Xu Copyright © 2022 Oranit Likhit et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 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. Hindawi Journal of Immunology Research Volume 2022, Article ID 5072154, 10 pages https://doi.org/10.1155/2022/5072154