• Sam Alahyari, Mohsen Rajaeinejad, Hasan Jalaeikhoo, and Davar Amani.
• Science and Research Branch, Faculty of Medicine, AJA University of Medical Sciences, Tehran, Iran.
• Arch Iran Med. 2022 Feb 1; 25 (2): 127-132.

BackgroundSevere cases of coronavirus disease 2019 (COVID-19) often experience hyper-inflammatory reactions, acute respiratory distress syndrome (ARDS), blood clotting, and organ damage. The most prominent immunopathology of advanced COVID-19 is cytokine release syndrome, or "cytokine storm" which is attributed to a defect of immune-regulating mechanisms. This study aimed to evaluate the role of regulatory T cells (Tregs) as one of the main cells that maintain immune homeostasis.MethodsA systematic search was performed on PubMed, Scopus and Google Scholar. All English articles related to Treg's role in COVID-19 were extracted and evaluated by two researchers independently. Study eligibility was assessed based on modified Evidence-based librarianship (EBL) checklist.ResultsNineteen eligible studies comparing Treg cells in COVID-19 patients with the control group or comparing alterations of this cell in severe and moderate patients were evaluated. Currently, there is no consensus regarding the increase or decrease of Tregs in COVID-19 patients compared to the control group. However, it was observed that Tregs in severe COVID-19 patients were significantly lower than moderate patients, resulting in uncontrolled inflammation and cytokine storm.ConclusionRegulatory T cells can be one of the determinants of disease severity and prognosis in patients with COVID-19 by inhibiting rampant inflammation and preventing cytokine storms.2022 The Author(s). This is an open-access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons. org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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