{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,3]],"date-time":"2026-06-03T22:07:29Z","timestamp":1780524449177,"version":"3.54.1"},"reference-count":42,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2021,4,14]],"date-time":"2021-04-14T00:00:00Z","timestamp":1618358400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Pediatr."],"abstract":"<jats:p><jats:bold>Introduction:<\/jats:bold> While pathogenesis in COVID-19 is not fully known and the effects between SARS-CoV-2 and the immune system are complicated, it is known that lymphopenia, hyper-inflammatory responses, and cytokines play an important role in the pathology of COVID-19. While some hematological abnormalities have been described among the laboratory features of COVID-19, there have not been studies reported on lymphocyte subset analyses in children. The aim of this study was to describe lymphocyte subsets in pediatric patients with mild\/moderate or severe COVID-19.<\/jats:p><jats:p><jats:bold>Methods:<\/jats:bold> The subjects in the study were children with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pneumonia confirmed with the real-time RT-PCR. The subjects were admitted to the Children's Medical Center, affiliated with the Tehran University of Medical Sciences, between March 7<jats:sup>th<\/jats:sup> and June 10<jats:sup>th<\/jats:sup> of 2020. The complete blood counts and lymphocyte subpopulations were analyzed for each patient.<\/jats:p><jats:p><jats:bold>Results:<\/jats:bold> The study included 55 hospitalized patients with confirmed SARS-CoV-2 infection (34 patients (62%) with an observed mild\/moderate case of the disease and 21 patients (38%) with severedisease). Lymphocyte counts were found to be lower in patients with a severe case (mean \u00b1 SD 1.6 \u00b1 0.9 in the severe group vs. 2.3 \u00b1 2.2 in the mild group). Compared to the group with mild\/moderate pneumonia, children with severe pneumonia had an increased count of CD8<jats:sup>+<\/jats:sup> T cell and a lower percentage of CD4<jats:sup>+<\/jats:sup> T cell. However, the differences between the groups were negligible. Interestingly, the severe group had a lower CD4<jats:sup>+<\/jats:sup>\/CD8<jats:sup>+<\/jats:sup> T cell ratio compared to the mild group (1.1 \u00b1 0.47 vs. 1.4 \u00b1 0.8, <jats:italic>p<\/jats:italic>-value: 0.063). CD4<jats:sup>+<\/jats:sup>\/CD8<jats:sup>+<\/jats:sup> T cell ratio &amp;lt;2, 1.5, and 1 was found in 48 (87%), 40 (73%), and 19 cases (35%). All of the seven cases in which the subject passed (13%) had CD4<jats:sup>+<\/jats:sup>\/CD8<jats:sup>+<\/jats:sup> T cell ratio of &amp;lt;2, 86% had CD4<jats:sup>+<\/jats:sup>\/CD8<jats:sup>+<\/jats:sup> T cell ratio of &amp;lt;1.5, and 29% had CD4<jats:sup>+<\/jats:sup>\/CD8<jats:sup>+<\/jats:sup> T cell ratio of &amp;lt;1.<\/jats:p><jats:p><jats:bold>Conclusion:<\/jats:bold> The CD4<jats:sup>+<\/jats:sup>\/CD8<jats:sup>+<\/jats:sup> T cell ratio was lower in patients with severe COVID-19 compared to those with mild\/moderate form of disease. However, although a decline in CD4<jats:sup>+<\/jats:sup>\/CD8<jats:sup>+<\/jats:sup> ratio may serve as a useful metric in analyzing of the derangement in immune responses in patients with severe COVID-19, further study with larger sample sizes is highly recommended.<\/jats:p>","DOI":"10.3389\/fped.2021.643299","type":"journal-article","created":{"date-parts":[[2021,4,14]],"date-time":"2021-04-14T06:22:35Z","timestamp":1618381355000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":18,"title":["Effects of Coronavirus Disease 2019 (COVID-19) on Peripheral Blood Lymphocytes and Their Subsets in Children: Imbalanced CD4+\/CD8+ T Cell Ratio and Disease 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